1----------------------------------------------------------------------------- 2This file contains a concatenation of the PCRE man pages, converted to plain 3text format for ease of searching with a text editor, or for use on systems 4that do not have a man page processor. The small individual files that give 5synopses of each function in the library have not been included. Neither has 6the pcredemo program. There are separate text files for the pcregrep and 7pcretest commands. 8----------------------------------------------------------------------------- 9 10 11PCRE(3) Library Functions Manual PCRE(3) 12 13 14 15NAME 16 PCRE - Perl-compatible regular expressions (original API) 17 18PLEASE TAKE NOTE 19 20 This document relates to PCRE releases that use the original API, with 21 library names libpcre, libpcre16, and libpcre32. January 2015 saw the 22 first release of a new API, known as PCRE2, with release numbers start- 23 ing at 10.00 and library names libpcre2-8, libpcre2-16, and 24 libpcre2-32. The old libraries (now called PCRE1) are still being main- 25 tained for bug fixes, but there will be no new development. New 26 projects are advised to use the new PCRE2 libraries. 27 28 29INTRODUCTION 30 31 The PCRE library is a set of functions that implement regular expres- 32 sion pattern matching using the same syntax and semantics as Perl, with 33 just a few differences. Some features that appeared in Python and PCRE 34 before they appeared in Perl are also available using the Python syn- 35 tax, there is some support for one or two .NET and Oniguruma syntax 36 items, and there is an option for requesting some minor changes that 37 give better JavaScript compatibility. 38 39 Starting with release 8.30, it is possible to compile two separate PCRE 40 libraries: the original, which supports 8-bit character strings 41 (including UTF-8 strings), and a second library that supports 16-bit 42 character strings (including UTF-16 strings). The build process allows 43 either one or both to be built. The majority of the work to make this 44 possible was done by Zoltan Herczeg. 45 46 Starting with release 8.32 it is possible to compile a third separate 47 PCRE library that supports 32-bit character strings (including UTF-32 48 strings). The build process allows any combination of the 8-, 16- and 49 32-bit libraries. The work to make this possible was done by Christian 50 Persch. 51 52 The three libraries contain identical sets of functions, except that 53 the names in the 16-bit library start with pcre16_ instead of pcre_, 54 and the names in the 32-bit library start with pcre32_ instead of 55 pcre_. To avoid over-complication and reduce the documentation mainte- 56 nance load, most of the documentation describes the 8-bit library, with 57 the differences for the 16-bit and 32-bit libraries described sepa- 58 rately in the pcre16 and pcre32 pages. References to functions or 59 structures of the form pcre[16|32]_xxx should be read as meaning 60 "pcre_xxx when using the 8-bit library, pcre16_xxx when using the 61 16-bit library, or pcre32_xxx when using the 32-bit library". 62 63 The current implementation of PCRE corresponds approximately with Perl 64 5.12, including support for UTF-8/16/32 encoded strings and Unicode 65 general category properties. However, UTF-8/16/32 and Unicode support 66 has to be explicitly enabled; it is not the default. The Unicode tables 67 correspond to Unicode release 6.3.0. 68 69 In addition to the Perl-compatible matching function, PCRE contains an 70 alternative function that matches the same compiled patterns in a dif- 71 ferent way. In certain circumstances, the alternative function has some 72 advantages. For a discussion of the two matching algorithms, see the 73 pcrematching page. 74 75 PCRE is written in C and released as a C library. A number of people 76 have written wrappers and interfaces of various kinds. In particular, 77 Google Inc. have provided a comprehensive C++ wrapper for the 8-bit 78 library. This is now included as part of the PCRE distribution. The 79 pcrecpp page has details of this interface. Other people's contribu- 80 tions can be found in the Contrib directory at the primary FTP site, 81 which is: 82 83 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre 84 85 Details of exactly which Perl regular expression features are and are 86 not supported by PCRE are given in separate documents. See the pcrepat- 87 tern and pcrecompat pages. There is a syntax summary in the pcresyntax 88 page. 89 90 Some features of PCRE can be included, excluded, or changed when the 91 library is built. The pcre_config() function makes it possible for a 92 client to discover which features are available. The features them- 93 selves are described in the pcrebuild page. Documentation about build- 94 ing PCRE for various operating systems can be found in the README and 95 NON-AUTOTOOLS_BUILD files in the source distribution. 96 97 The libraries contains a number of undocumented internal functions and 98 data tables that are used by more than one of the exported external 99 functions, but which are not intended for use by external callers. 100 Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which 101 hopefully will not provoke any name clashes. In some environments, it 102 is possible to control which external symbols are exported when a 103 shared library is built, and in these cases the undocumented symbols 104 are not exported. 105 106 107SECURITY CONSIDERATIONS 108 109 If you are using PCRE in a non-UTF application that permits users to 110 supply arbitrary patterns for compilation, you should be aware of a 111 feature that allows users to turn on UTF support from within a pattern, 112 provided that PCRE was built with UTF support. For example, an 8-bit 113 pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, 114 which interprets patterns and subjects as strings of UTF-8 characters 115 instead of individual 8-bit characters. This causes both the pattern 116 and any data against which it is matched to be checked for UTF-8 valid- 117 ity. If the data string is very long, such a check might use suffi- 118 ciently many resources as to cause your application to lose perfor- 119 mance. 120 121 One way of guarding against this possibility is to use the 122 pcre_fullinfo() function to check the compiled pattern's options for 123 UTF. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF 124 option at compile time. This causes an compile time error if a pattern 125 contains a UTF-setting sequence. 126 127 If your application is one that supports UTF, be aware that validity 128 checking can take time. If the same data string is to be matched many 129 times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second 130 and subsequent matches to save redundant checks. 131 132 Another way that performance can be hit is by running a pattern that 133 has a very large search tree against a string that will never match. 134 Nested unlimited repeats in a pattern are a common example. PCRE pro- 135 vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea- 136 ture in the pcreapi page. 137 138 139USER DOCUMENTATION 140 141 The user documentation for PCRE comprises a number of different sec- 142 tions. In the "man" format, each of these is a separate "man page". In 143 the HTML format, each is a separate page, linked from the index page. 144 In the plain text format, the descriptions of the pcregrep and pcretest 145 programs are in files called pcregrep.txt and pcretest.txt, respec- 146 tively. The remaining sections, except for the pcredemo section (which 147 is a program listing), are concatenated in pcre.txt, for ease of 148 searching. The sections are as follows: 149 150 pcre this document 151 pcre-config show PCRE installation configuration information 152 pcre16 details of the 16-bit library 153 pcre32 details of the 32-bit library 154 pcreapi details of PCRE's native C API 155 pcrebuild building PCRE 156 pcrecallout details of the callout feature 157 pcrecompat discussion of Perl compatibility 158 pcrecpp details of the C++ wrapper for the 8-bit library 159 pcredemo a demonstration C program that uses PCRE 160 pcregrep description of the pcregrep command (8-bit only) 161 pcrejit discussion of the just-in-time optimization support 162 pcrelimits details of size and other limits 163 pcrematching discussion of the two matching algorithms 164 pcrepartial details of the partial matching facility 165 pcrepattern syntax and semantics of supported 166 regular expressions 167 pcreperform discussion of performance issues 168 pcreposix the POSIX-compatible C API for the 8-bit library 169 pcreprecompile details of saving and re-using precompiled patterns 170 pcresample discussion of the pcredemo program 171 pcrestack discussion of stack usage 172 pcresyntax quick syntax reference 173 pcretest description of the pcretest testing command 174 pcreunicode discussion of Unicode and UTF-8/16/32 support 175 176 In the "man" and HTML formats, there is also a short page for each C 177 library function, listing its arguments and results. 178 179 180AUTHOR 181 182 Philip Hazel 183 University Computing Service 184 Cambridge CB2 3QH, England. 185 186 Putting an actual email address here seems to have been a spam magnet, 187 so I've taken it away. If you want to email me, use my two initials, 188 followed by the two digits 10, at the domain cam.ac.uk. 189 190 191REVISION 192 193 Last updated: 10 February 2015 194 Copyright (c) 1997-2015 University of Cambridge. 195------------------------------------------------------------------------------ 196 197 198PCRE(3) Library Functions Manual PCRE(3) 199 200 201 202NAME 203 PCRE - Perl-compatible regular expressions 204 205 #include <pcre.h> 206 207 208PCRE 16-BIT API BASIC FUNCTIONS 209 210 pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options, 211 const char **errptr, int *erroffset, 212 const unsigned char *tableptr); 213 214 pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options, 215 int *errorcodeptr, 216 const char **errptr, int *erroffset, 217 const unsigned char *tableptr); 218 219 pcre16_extra *pcre16_study(const pcre16 *code, int options, 220 const char **errptr); 221 222 void pcre16_free_study(pcre16_extra *extra); 223 224 int pcre16_exec(const pcre16 *code, const pcre16_extra *extra, 225 PCRE_SPTR16 subject, int length, int startoffset, 226 int options, int *ovector, int ovecsize); 227 228 int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra, 229 PCRE_SPTR16 subject, int length, int startoffset, 230 int options, int *ovector, int ovecsize, 231 int *workspace, int wscount); 232 233 234PCRE 16-BIT API STRING EXTRACTION FUNCTIONS 235 236 int pcre16_copy_named_substring(const pcre16 *code, 237 PCRE_SPTR16 subject, int *ovector, 238 int stringcount, PCRE_SPTR16 stringname, 239 PCRE_UCHAR16 *buffer, int buffersize); 240 241 int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector, 242 int stringcount, int stringnumber, PCRE_UCHAR16 *buffer, 243 int buffersize); 244 245 int pcre16_get_named_substring(const pcre16 *code, 246 PCRE_SPTR16 subject, int *ovector, 247 int stringcount, PCRE_SPTR16 stringname, 248 PCRE_SPTR16 *stringptr); 249 250 int pcre16_get_stringnumber(const pcre16 *code, 251 PCRE_SPTR16 name); 252 253 int pcre16_get_stringtable_entries(const pcre16 *code, 254 PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last); 255 256 int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector, 257 int stringcount, int stringnumber, 258 PCRE_SPTR16 *stringptr); 259 260 int pcre16_get_substring_list(PCRE_SPTR16 subject, 261 int *ovector, int stringcount, PCRE_SPTR16 **listptr); 262 263 void pcre16_free_substring(PCRE_SPTR16 stringptr); 264 265 void pcre16_free_substring_list(PCRE_SPTR16 *stringptr); 266 267 268PCRE 16-BIT API AUXILIARY FUNCTIONS 269 270 pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize); 271 272 void pcre16_jit_stack_free(pcre16_jit_stack *stack); 273 274 void pcre16_assign_jit_stack(pcre16_extra *extra, 275 pcre16_jit_callback callback, void *data); 276 277 const unsigned char *pcre16_maketables(void); 278 279 int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra, 280 int what, void *where); 281 282 int pcre16_refcount(pcre16 *code, int adjust); 283 284 int pcre16_config(int what, void *where); 285 286 const char *pcre16_version(void); 287 288 int pcre16_pattern_to_host_byte_order(pcre16 *code, 289 pcre16_extra *extra, const unsigned char *tables); 290 291 292PCRE 16-BIT API INDIRECTED FUNCTIONS 293 294 void *(*pcre16_malloc)(size_t); 295 296 void (*pcre16_free)(void *); 297 298 void *(*pcre16_stack_malloc)(size_t); 299 300 void (*pcre16_stack_free)(void *); 301 302 int (*pcre16_callout)(pcre16_callout_block *); 303 304 305PCRE 16-BIT API 16-BIT-ONLY FUNCTION 306 307 int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output, 308 PCRE_SPTR16 input, int length, int *byte_order, 309 int keep_boms); 310 311 312THE PCRE 16-BIT LIBRARY 313 314 Starting with release 8.30, it is possible to compile a PCRE library 315 that supports 16-bit character strings, including UTF-16 strings, as 316 well as or instead of the original 8-bit library. The majority of the 317 work to make this possible was done by Zoltan Herczeg. The two 318 libraries contain identical sets of functions, used in exactly the same 319 way. Only the names of the functions and the data types of their argu- 320 ments and results are different. To avoid over-complication and reduce 321 the documentation maintenance load, most of the PCRE documentation 322 describes the 8-bit library, with only occasional references to the 323 16-bit library. This page describes what is different when you use the 324 16-bit library. 325 326 WARNING: A single application can be linked with both libraries, but 327 you must take care when processing any particular pattern to use func- 328 tions from just one library. For example, if you want to study a pat- 329 tern that was compiled with pcre16_compile(), you must do so with 330 pcre16_study(), not pcre_study(), and you must free the study data with 331 pcre16_free_study(). 332 333 334THE HEADER FILE 335 336 There is only one header file, pcre.h. It contains prototypes for all 337 the functions in all libraries, as well as definitions of flags, struc- 338 tures, error codes, etc. 339 340 341THE LIBRARY NAME 342 343 In Unix-like systems, the 16-bit library is called libpcre16, and can 344 normally be accesss by adding -lpcre16 to the command for linking an 345 application that uses PCRE. 346 347 348STRING TYPES 349 350 In the 8-bit library, strings are passed to PCRE library functions as 351 vectors of bytes with the C type "char *". In the 16-bit library, 352 strings are passed as vectors of unsigned 16-bit quantities. The macro 353 PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is 354 defined as "const PCRE_UCHAR16 *". In very many environments, "short 355 int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16 356 as "unsigned short int", but checks that it really is a 16-bit data 357 type. If it is not, the build fails with an error message telling the 358 maintainer to modify the definition appropriately. 359 360 361STRUCTURE TYPES 362 363 The types of the opaque structures that are used for compiled 16-bit 364 patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively. 365 The type of the user-accessible structure that is returned by 366 pcre16_study() is pcre16_extra, and the type of the structure that is 367 used for passing data to a callout function is pcre16_callout_block. 368 These structures contain the same fields, with the same names, as their 369 8-bit counterparts. The only difference is that pointers to character 370 strings are 16-bit instead of 8-bit types. 371 372 37316-BIT FUNCTIONS 374 375 For every function in the 8-bit library there is a corresponding func- 376 tion in the 16-bit library with a name that starts with pcre16_ instead 377 of pcre_. The prototypes are listed above. In addition, there is one 378 extra function, pcre16_utf16_to_host_byte_order(). This is a utility 379 function that converts a UTF-16 character string to host byte order if 380 necessary. The other 16-bit functions expect the strings they are 381 passed to be in host byte order. 382 383 The input and output arguments of pcre16_utf16_to_host_byte_order() may 384 point to the same address, that is, conversion in place is supported. 385 The output buffer must be at least as long as the input. 386 387 The length argument specifies the number of 16-bit data units in the 388 input string; a negative value specifies a zero-terminated string. 389 390 If byte_order is NULL, it is assumed that the string starts off in host 391 byte order. This may be changed by byte-order marks (BOMs) anywhere in 392 the string (commonly as the first character). 393 394 If byte_order is not NULL, a non-zero value of the integer to which it 395 points means that the input starts off in host byte order, otherwise 396 the opposite order is assumed. Again, BOMs in the string can change 397 this. The final byte order is passed back at the end of processing. 398 399 If keep_boms is not zero, byte-order mark characters (0xfeff) are 400 copied into the output string. Otherwise they are discarded. 401 402 The result of the function is the number of 16-bit units placed into 403 the output buffer, including the zero terminator if the string was 404 zero-terminated. 405 406 407SUBJECT STRING OFFSETS 408 409 The lengths and starting offsets of subject strings must be specified 410 in 16-bit data units, and the offsets within subject strings that are 411 returned by the matching functions are in also 16-bit units rather than 412 bytes. 413 414 415NAMED SUBPATTERNS 416 417 The name-to-number translation table that is maintained for named sub- 418 patterns uses 16-bit characters. The pcre16_get_stringtable_entries() 419 function returns the length of each entry in the table as the number of 420 16-bit data units. 421 422 423OPTION NAMES 424 425 There are two new general option names, PCRE_UTF16 and 426 PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and 427 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options 428 define the same bits in the options word. There is a discussion about 429 the validity of UTF-16 strings in the pcreunicode page. 430 431 For the pcre16_config() function there is an option PCRE_CONFIG_UTF16 432 that returns 1 if UTF-16 support is configured, otherwise 0. If this 433 option is given to pcre_config() or pcre32_config(), or if the 434 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con- 435 fig(), the result is the PCRE_ERROR_BADOPTION error. 436 437 438CHARACTER CODES 439 440 In 16-bit mode, when PCRE_UTF16 is not set, character values are 441 treated in the same way as in 8-bit, non UTF-8 mode, except, of course, 442 that they can range from 0 to 0xffff instead of 0 to 0xff. Character 443 types for characters less than 0xff can therefore be influenced by the 444 locale in the same way as before. Characters greater than 0xff have 445 only one case, and no "type" (such as letter or digit). 446 447 In UTF-16 mode, the character code is Unicode, in the range 0 to 448 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff 449 because those are "surrogate" values that are used in pairs to encode 450 values greater than 0xffff. 451 452 A UTF-16 string can indicate its endianness by special code knows as a 453 byte-order mark (BOM). The PCRE functions do not handle this, expecting 454 strings to be in host byte order. A utility function called 455 pcre16_utf16_to_host_byte_order() is provided to help with this (see 456 above). 457 458 459ERROR NAMES 460 461 The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre- 462 spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is 463 given when a compiled pattern is passed to a function that processes 464 patterns in the other mode, for example, if a pattern compiled with 465 pcre_compile() is passed to pcre16_exec(). 466 467 There are new error codes whose names begin with PCRE_UTF16_ERR for 468 invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for 469 UTF-8 strings that are described in the section entitled "Reason codes 470 for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors 471 are: 472 473 PCRE_UTF16_ERR1 Missing low surrogate at end of string 474 PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate 475 PCRE_UTF16_ERR3 Isolated low surrogate 476 PCRE_UTF16_ERR4 Non-character 477 478 479ERROR TEXTS 480 481 If there is an error while compiling a pattern, the error text that is 482 passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit 483 character string, zero-terminated. 484 485 486CALLOUTS 487 488 The subject and mark fields in the callout block that is passed to a 489 callout function point to 16-bit vectors. 490 491 492TESTING 493 494 The pcretest program continues to operate with 8-bit input and output 495 files, but it can be used for testing the 16-bit library. If it is run 496 with the command line option -16, patterns and subject strings are con- 497 verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit 498 library functions are used instead of the 8-bit ones. Returned 16-bit 499 strings are converted to 8-bit for output. If both the 8-bit and the 500 32-bit libraries were not compiled, pcretest defaults to 16-bit and the 501 -16 option is ignored. 502 503 When PCRE is being built, the RunTest script that is called by "make 504 check" uses the pcretest -C option to discover which of the 8-bit, 505 16-bit and 32-bit libraries has been built, and runs the tests appro- 506 priately. 507 508 509NOT SUPPORTED IN 16-BIT MODE 510 511 Not all the features of the 8-bit library are available with the 16-bit 512 library. The C++ and POSIX wrapper functions support only the 8-bit 513 library, and the pcregrep program is at present 8-bit only. 514 515 516AUTHOR 517 518 Philip Hazel 519 University Computing Service 520 Cambridge CB2 3QH, England. 521 522 523REVISION 524 525 Last updated: 12 May 2013 526 Copyright (c) 1997-2013 University of Cambridge. 527------------------------------------------------------------------------------ 528 529 530PCRE(3) Library Functions Manual PCRE(3) 531 532 533 534NAME 535 PCRE - Perl-compatible regular expressions 536 537 #include <pcre.h> 538 539 540PCRE 32-BIT API BASIC FUNCTIONS 541 542 pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options, 543 const char **errptr, int *erroffset, 544 const unsigned char *tableptr); 545 546 pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options, 547 int *errorcodeptr, 548 const unsigned char *tableptr); 549 550 pcre32_extra *pcre32_study(const pcre32 *code, int options, 551 const char **errptr); 552 553 void pcre32_free_study(pcre32_extra *extra); 554 555 int pcre32_exec(const pcre32 *code, const pcre32_extra *extra, 556 PCRE_SPTR32 subject, int length, int startoffset, 557 int options, int *ovector, int ovecsize); 558 559 int pcre32_dfa_exec(const pcre32 *code, const pcre32_extra *extra, 560 PCRE_SPTR32 subject, int length, int startoffset, 561 int options, int *ovector, int ovecsize, 562 int *workspace, int wscount); 563 564 565PCRE 32-BIT API STRING EXTRACTION FUNCTIONS 566 567 int pcre32_copy_named_substring(const pcre32 *code, 568 PCRE_SPTR32 subject, int *ovector, 569 int stringcount, PCRE_SPTR32 stringname, 570 PCRE_UCHAR32 *buffer, int buffersize); 571 572 int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector, 573 int stringcount, int stringnumber, PCRE_UCHAR32 *buffer, 574 int buffersize); 575 576 int pcre32_get_named_substring(const pcre32 *code, 577 PCRE_SPTR32 subject, int *ovector, 578 int stringcount, PCRE_SPTR32 stringname, 579 PCRE_SPTR32 *stringptr); 580 581 int pcre32_get_stringnumber(const pcre32 *code, 582 PCRE_SPTR32 name); 583 584 int pcre32_get_stringtable_entries(const pcre32 *code, 585 PCRE_SPTR32 name, PCRE_UCHAR32 **first, PCRE_UCHAR32 **last); 586 587 int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector, 588 int stringcount, int stringnumber, 589 PCRE_SPTR32 *stringptr); 590 591 int pcre32_get_substring_list(PCRE_SPTR32 subject, 592 int *ovector, int stringcount, PCRE_SPTR32 **listptr); 593 594 void pcre32_free_substring(PCRE_SPTR32 stringptr); 595 596 void pcre32_free_substring_list(PCRE_SPTR32 *stringptr); 597 598 599PCRE 32-BIT API AUXILIARY FUNCTIONS 600 601 pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize); 602 603 void pcre32_jit_stack_free(pcre32_jit_stack *stack); 604 605 void pcre32_assign_jit_stack(pcre32_extra *extra, 606 pcre32_jit_callback callback, void *data); 607 608 const unsigned char *pcre32_maketables(void); 609 610 int pcre32_fullinfo(const pcre32 *code, const pcre32_extra *extra, 611 int what, void *where); 612 613 int pcre32_refcount(pcre32 *code, int adjust); 614 615 int pcre32_config(int what, void *where); 616 617 const char *pcre32_version(void); 618 619 int pcre32_pattern_to_host_byte_order(pcre32 *code, 620 pcre32_extra *extra, const unsigned char *tables); 621 622 623PCRE 32-BIT API INDIRECTED FUNCTIONS 624 625 void *(*pcre32_malloc)(size_t); 626 627 void (*pcre32_free)(void *); 628 629 void *(*pcre32_stack_malloc)(size_t); 630 631 void (*pcre32_stack_free)(void *); 632 633 int (*pcre32_callout)(pcre32_callout_block *); 634 635 636PCRE 32-BIT API 32-BIT-ONLY FUNCTION 637 638 int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output, 639 PCRE_SPTR32 input, int length, int *byte_order, 640 int keep_boms); 641 642 643THE PCRE 32-BIT LIBRARY 644 645 Starting with release 8.32, it is possible to compile a PCRE library 646 that supports 32-bit character strings, including UTF-32 strings, as 647 well as or instead of the original 8-bit library. This work was done by 648 Christian Persch, based on the work done by Zoltan Herczeg for the 649 16-bit library. All three libraries contain identical sets of func- 650 tions, used in exactly the same way. Only the names of the functions 651 and the data types of their arguments and results are different. To 652 avoid over-complication and reduce the documentation maintenance load, 653 most of the PCRE documentation describes the 8-bit library, with only 654 occasional references to the 16-bit and 32-bit libraries. This page 655 describes what is different when you use the 32-bit library. 656 657 WARNING: A single application can be linked with all or any of the 658 three libraries, but you must take care when processing any particular 659 pattern to use functions from just one library. For example, if you 660 want to study a pattern that was compiled with pcre32_compile(), you 661 must do so with pcre32_study(), not pcre_study(), and you must free the 662 study data with pcre32_free_study(). 663 664 665THE HEADER FILE 666 667 There is only one header file, pcre.h. It contains prototypes for all 668 the functions in all libraries, as well as definitions of flags, struc- 669 tures, error codes, etc. 670 671 672THE LIBRARY NAME 673 674 In Unix-like systems, the 32-bit library is called libpcre32, and can 675 normally be accesss by adding -lpcre32 to the command for linking an 676 application that uses PCRE. 677 678 679STRING TYPES 680 681 In the 8-bit library, strings are passed to PCRE library functions as 682 vectors of bytes with the C type "char *". In the 32-bit library, 683 strings are passed as vectors of unsigned 32-bit quantities. The macro 684 PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is 685 defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned 686 int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32 687 as "unsigned int", but checks that it really is a 32-bit data type. If 688 it is not, the build fails with an error message telling the maintainer 689 to modify the definition appropriately. 690 691 692STRUCTURE TYPES 693 694 The types of the opaque structures that are used for compiled 32-bit 695 patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively. 696 The type of the user-accessible structure that is returned by 697 pcre32_study() is pcre32_extra, and the type of the structure that is 698 used for passing data to a callout function is pcre32_callout_block. 699 These structures contain the same fields, with the same names, as their 700 8-bit counterparts. The only difference is that pointers to character 701 strings are 32-bit instead of 8-bit types. 702 703 70432-BIT FUNCTIONS 705 706 For every function in the 8-bit library there is a corresponding func- 707 tion in the 32-bit library with a name that starts with pcre32_ instead 708 of pcre_. The prototypes are listed above. In addition, there is one 709 extra function, pcre32_utf32_to_host_byte_order(). This is a utility 710 function that converts a UTF-32 character string to host byte order if 711 necessary. The other 32-bit functions expect the strings they are 712 passed to be in host byte order. 713 714 The input and output arguments of pcre32_utf32_to_host_byte_order() may 715 point to the same address, that is, conversion in place is supported. 716 The output buffer must be at least as long as the input. 717 718 The length argument specifies the number of 32-bit data units in the 719 input string; a negative value specifies a zero-terminated string. 720 721 If byte_order is NULL, it is assumed that the string starts off in host 722 byte order. This may be changed by byte-order marks (BOMs) anywhere in 723 the string (commonly as the first character). 724 725 If byte_order is not NULL, a non-zero value of the integer to which it 726 points means that the input starts off in host byte order, otherwise 727 the opposite order is assumed. Again, BOMs in the string can change 728 this. The final byte order is passed back at the end of processing. 729 730 If keep_boms is not zero, byte-order mark characters (0xfeff) are 731 copied into the output string. Otherwise they are discarded. 732 733 The result of the function is the number of 32-bit units placed into 734 the output buffer, including the zero terminator if the string was 735 zero-terminated. 736 737 738SUBJECT STRING OFFSETS 739 740 The lengths and starting offsets of subject strings must be specified 741 in 32-bit data units, and the offsets within subject strings that are 742 returned by the matching functions are in also 32-bit units rather than 743 bytes. 744 745 746NAMED SUBPATTERNS 747 748 The name-to-number translation table that is maintained for named sub- 749 patterns uses 32-bit characters. The pcre32_get_stringtable_entries() 750 function returns the length of each entry in the table as the number of 751 32-bit data units. 752 753 754OPTION NAMES 755 756 There are two new general option names, PCRE_UTF32 and 757 PCRE_NO_UTF32_CHECK, which correspond to PCRE_UTF8 and 758 PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options 759 define the same bits in the options word. There is a discussion about 760 the validity of UTF-32 strings in the pcreunicode page. 761 762 For the pcre32_config() function there is an option PCRE_CONFIG_UTF32 763 that returns 1 if UTF-32 support is configured, otherwise 0. If this 764 option is given to pcre_config() or pcre16_config(), or if the 765 PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con- 766 fig(), the result is the PCRE_ERROR_BADOPTION error. 767 768 769CHARACTER CODES 770 771 In 32-bit mode, when PCRE_UTF32 is not set, character values are 772 treated in the same way as in 8-bit, non UTF-8 mode, except, of course, 773 that they can range from 0 to 0x7fffffff instead of 0 to 0xff. Charac- 774 ter types for characters less than 0xff can therefore be influenced by 775 the locale in the same way as before. Characters greater than 0xff 776 have only one case, and no "type" (such as letter or digit). 777 778 In UTF-32 mode, the character code is Unicode, in the range 0 to 779 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff 780 because those are "surrogate" values that are ill-formed in UTF-32. 781 782 A UTF-32 string can indicate its endianness by special code knows as a 783 byte-order mark (BOM). The PCRE functions do not handle this, expecting 784 strings to be in host byte order. A utility function called 785 pcre32_utf32_to_host_byte_order() is provided to help with this (see 786 above). 787 788 789ERROR NAMES 790 791 The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart. 792 The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed 793 to a function that processes patterns in the other mode, for example, 794 if a pattern compiled with pcre_compile() is passed to pcre32_exec(). 795 796 There are new error codes whose names begin with PCRE_UTF32_ERR for 797 invalid UTF-32 strings, corresponding to the PCRE_UTF8_ERR codes for 798 UTF-8 strings that are described in the section entitled "Reason codes 799 for invalid UTF-8 strings" in the main pcreapi page. The UTF-32 errors 800 are: 801 802 PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff) 803 PCRE_UTF32_ERR2 Non-character 804 PCRE_UTF32_ERR3 Character > 0x10ffff 805 806 807ERROR TEXTS 808 809 If there is an error while compiling a pattern, the error text that is 810 passed back by pcre32_compile() or pcre32_compile2() is still an 8-bit 811 character string, zero-terminated. 812 813 814CALLOUTS 815 816 The subject and mark fields in the callout block that is passed to a 817 callout function point to 32-bit vectors. 818 819 820TESTING 821 822 The pcretest program continues to operate with 8-bit input and output 823 files, but it can be used for testing the 32-bit library. If it is run 824 with the command line option -32, patterns and subject strings are con- 825 verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit 826 library functions are used instead of the 8-bit ones. Returned 32-bit 827 strings are converted to 8-bit for output. If both the 8-bit and the 828 16-bit libraries were not compiled, pcretest defaults to 32-bit and the 829 -32 option is ignored. 830 831 When PCRE is being built, the RunTest script that is called by "make 832 check" uses the pcretest -C option to discover which of the 8-bit, 833 16-bit and 32-bit libraries has been built, and runs the tests appro- 834 priately. 835 836 837NOT SUPPORTED IN 32-BIT MODE 838 839 Not all the features of the 8-bit library are available with the 32-bit 840 library. The C++ and POSIX wrapper functions support only the 8-bit 841 library, and the pcregrep program is at present 8-bit only. 842 843 844AUTHOR 845 846 Philip Hazel 847 University Computing Service 848 Cambridge CB2 3QH, England. 849 850 851REVISION 852 853 Last updated: 12 May 2013 854 Copyright (c) 1997-2013 University of Cambridge. 855------------------------------------------------------------------------------ 856 857 858PCREBUILD(3) Library Functions Manual PCREBUILD(3) 859 860 861 862NAME 863 PCRE - Perl-compatible regular expressions 864 865BUILDING PCRE 866 867 PCRE is distributed with a configure script that can be used to build 868 the library in Unix-like environments using the applications known as 869 Autotools. Also in the distribution are files to support building 870 using CMake instead of configure. The text file README contains general 871 information about building with Autotools (some of which is repeated 872 below), and also has some comments about building on various operating 873 systems. There is a lot more information about building PCRE without 874 using Autotools (including information about using CMake and building 875 "by hand") in the text file called NON-AUTOTOOLS-BUILD. You should 876 consult this file as well as the README file if you are building in a 877 non-Unix-like environment. 878 879 880PCRE BUILD-TIME OPTIONS 881 882 The rest of this document describes the optional features of PCRE that 883 can be selected when the library is compiled. It assumes use of the 884 configure script, where the optional features are selected or dese- 885 lected by providing options to configure before running the make com- 886 mand. However, the same options can be selected in both Unix-like and 887 non-Unix-like environments using the GUI facility of cmake-gui if you 888 are using CMake instead of configure to build PCRE. 889 890 If you are not using Autotools or CMake, option selection can be done 891 by editing the config.h file, or by passing parameter settings to the 892 compiler, as described in NON-AUTOTOOLS-BUILD. 893 894 The complete list of options for configure (which includes the standard 895 ones such as the selection of the installation directory) can be 896 obtained by running 897 898 ./configure --help 899 900 The following sections include descriptions of options whose names 901 begin with --enable or --disable. These settings specify changes to the 902 defaults for the configure command. Because of the way that configure 903 works, --enable and --disable always come in pairs, so the complemen- 904 tary option always exists as well, but as it specifies the default, it 905 is not described. 906 907 908BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES 909 910 By default, a library called libpcre is built, containing functions 911 that take string arguments contained in vectors of bytes, either as 912 single-byte characters, or interpreted as UTF-8 strings. You can also 913 build a separate library, called libpcre16, in which strings are con- 914 tained in vectors of 16-bit data units and interpreted either as sin- 915 gle-unit characters or UTF-16 strings, by adding 916 917 --enable-pcre16 918 919 to the configure command. You can also build yet another separate 920 library, called libpcre32, in which strings are contained in vectors of 921 32-bit data units and interpreted either as single-unit characters or 922 UTF-32 strings, by adding 923 924 --enable-pcre32 925 926 to the configure command. If you do not want the 8-bit library, add 927 928 --disable-pcre8 929 930 as well. At least one of the three libraries must be built. Note that 931 the C++ and POSIX wrappers are for the 8-bit library only, and that 932 pcregrep is an 8-bit program. None of these are built if you select 933 only the 16-bit or 32-bit libraries. 934 935 936BUILDING SHARED AND STATIC LIBRARIES 937 938 The Autotools PCRE building process uses libtool to build both shared 939 and static libraries by default. You can suppress one of these by 940 adding one of 941 942 --disable-shared 943 --disable-static 944 945 to the configure command, as required. 946 947 948C++ SUPPORT 949 950 By default, if the 8-bit library is being built, the configure script 951 will search for a C++ compiler and C++ header files. If it finds them, 952 it automatically builds the C++ wrapper library (which supports only 953 8-bit strings). You can disable this by adding 954 955 --disable-cpp 956 957 to the configure command. 958 959 960UTF-8, UTF-16 AND UTF-32 SUPPORT 961 962 To build PCRE with support for UTF Unicode character strings, add 963 964 --enable-utf 965 966 to the configure command. This setting applies to all three libraries, 967 adding support for UTF-8 to the 8-bit library, support for UTF-16 to 968 the 16-bit library, and support for UTF-32 to the to the 32-bit 969 library. There are no separate options for enabling UTF-8, UTF-16 and 970 UTF-32 independently because that would allow ridiculous settings such 971 as requesting UTF-16 support while building only the 8-bit library. It 972 is not possible to build one library with UTF support and another with- 973 out in the same configuration. (For backwards compatibility, --enable- 974 utf8 is a synonym of --enable-utf.) 975 976 Of itself, this setting does not make PCRE treat strings as UTF-8, 977 UTF-16 or UTF-32. As well as compiling PCRE with this option, you also 978 have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as 979 appropriate) when you call one of the pattern compiling functions. 980 981 If you set --enable-utf when compiling in an EBCDIC environment, PCRE 982 expects its input to be either ASCII or UTF-8 (depending on the run- 983 time option). It is not possible to support both EBCDIC and UTF-8 codes 984 in the same version of the library. Consequently, --enable-utf and 985 --enable-ebcdic are mutually exclusive. 986 987 988UNICODE CHARACTER PROPERTY SUPPORT 989 990 UTF support allows the libraries to process character codepoints up to 991 0x10ffff in the strings that they handle. On its own, however, it does 992 not provide any facilities for accessing the properties of such charac- 993 ters. If you want to be able to use the pattern escapes \P, \p, and \X, 994 which refer to Unicode character properties, you must add 995 996 --enable-unicode-properties 997 998 to the configure command. This implies UTF support, even if you have 999 not explicitly requested it. 1000 1001 Including Unicode property support adds around 30K of tables to the 1002 PCRE library. Only the general category properties such as Lu and Nd 1003 are supported. Details are given in the pcrepattern documentation. 1004 1005 1006JUST-IN-TIME COMPILER SUPPORT 1007 1008 Just-in-time compiler support is included in the build by specifying 1009 1010 --enable-jit 1011 1012 This support is available only for certain hardware architectures. If 1013 this option is set for an unsupported architecture, a compile time 1014 error occurs. See the pcrejit documentation for a discussion of JIT 1015 usage. When JIT support is enabled, pcregrep automatically makes use of 1016 it, unless you add 1017 1018 --disable-pcregrep-jit 1019 1020 to the "configure" command. 1021 1022 1023CODE VALUE OF NEWLINE 1024 1025 By default, PCRE interprets the linefeed (LF) character as indicating 1026 the end of a line. This is the normal newline character on Unix-like 1027 systems. You can compile PCRE to use carriage return (CR) instead, by 1028 adding 1029 1030 --enable-newline-is-cr 1031 1032 to the configure command. There is also a --enable-newline-is-lf 1033 option, which explicitly specifies linefeed as the newline character. 1034 1035 Alternatively, you can specify that line endings are to be indicated by 1036 the two character sequence CRLF. If you want this, add 1037 1038 --enable-newline-is-crlf 1039 1040 to the configure command. There is a fourth option, specified by 1041 1042 --enable-newline-is-anycrlf 1043 1044 which causes PCRE to recognize any of the three sequences CR, LF, or 1045 CRLF as indicating a line ending. Finally, a fifth option, specified by 1046 1047 --enable-newline-is-any 1048 1049 causes PCRE to recognize any Unicode newline sequence. 1050 1051 Whatever line ending convention is selected when PCRE is built can be 1052 overridden when the library functions are called. At build time it is 1053 conventional to use the standard for your operating system. 1054 1055 1056WHAT \R MATCHES 1057 1058 By default, the sequence \R in a pattern matches any Unicode newline 1059 sequence, whatever has been selected as the line ending sequence. If 1060 you specify 1061 1062 --enable-bsr-anycrlf 1063 1064 the default is changed so that \R matches only CR, LF, or CRLF. What- 1065 ever is selected when PCRE is built can be overridden when the library 1066 functions are called. 1067 1068 1069POSIX MALLOC USAGE 1070 1071 When the 8-bit library is called through the POSIX interface (see the 1072 pcreposix documentation), additional working storage is required for 1073 holding the pointers to capturing substrings, because PCRE requires 1074 three integers per substring, whereas the POSIX interface provides only 1075 two. If the number of expected substrings is small, the wrapper func- 1076 tion uses space on the stack, because this is faster than using mal- 1077 loc() for each call. The default threshold above which the stack is no 1078 longer used is 10; it can be changed by adding a setting such as 1079 1080 --with-posix-malloc-threshold=20 1081 1082 to the configure command. 1083 1084 1085HANDLING VERY LARGE PATTERNS 1086 1087 Within a compiled pattern, offset values are used to point from one 1088 part to another (for example, from an opening parenthesis to an alter- 1089 nation metacharacter). By default, in the 8-bit and 16-bit libraries, 1090 two-byte values are used for these offsets, leading to a maximum size 1091 for a compiled pattern of around 64K. This is sufficient to handle all 1092 but the most gigantic patterns. Nevertheless, some people do want to 1093 process truly enormous patterns, so it is possible to compile PCRE to 1094 use three-byte or four-byte offsets by adding a setting such as 1095 1096 --with-link-size=3 1097 1098 to the configure command. The value given must be 2, 3, or 4. For the 1099 16-bit library, a value of 3 is rounded up to 4. In these libraries, 1100 using longer offsets slows down the operation of PCRE because it has to 1101 load additional data when handling them. For the 32-bit library the 1102 value is always 4 and cannot be overridden; the value of --with-link- 1103 size is ignored. 1104 1105 1106AVOIDING EXCESSIVE STACK USAGE 1107 1108 When matching with the pcre_exec() function, PCRE implements backtrack- 1109 ing by making recursive calls to an internal function called match(). 1110 In environments where the size of the stack is limited, this can se- 1111 verely limit PCRE's operation. (The Unix environment does not usually 1112 suffer from this problem, but it may sometimes be necessary to increase 1113 the maximum stack size. There is a discussion in the pcrestack docu- 1114 mentation.) An alternative approach to recursion that uses memory from 1115 the heap to remember data, instead of using recursive function calls, 1116 has been implemented to work round the problem of limited stack size. 1117 If you want to build a version of PCRE that works this way, add 1118 1119 --disable-stack-for-recursion 1120 1121 to the configure command. With this configuration, PCRE will use the 1122 pcre_stack_malloc and pcre_stack_free variables to call memory manage- 1123 ment functions. By default these point to malloc() and free(), but you 1124 can replace the pointers so that your own functions are used instead. 1125 1126 Separate functions are provided rather than using pcre_malloc and 1127 pcre_free because the usage is very predictable: the block sizes 1128 requested are always the same, and the blocks are always freed in 1129 reverse order. A calling program might be able to implement optimized 1130 functions that perform better than malloc() and free(). PCRE runs 1131 noticeably more slowly when built in this way. This option affects only 1132 the pcre_exec() function; it is not relevant for pcre_dfa_exec(). 1133 1134 1135LIMITING PCRE RESOURCE USAGE 1136 1137 Internally, PCRE has a function called match(), which it calls repeat- 1138 edly (sometimes recursively) when matching a pattern with the 1139 pcre_exec() function. By controlling the maximum number of times this 1140 function may be called during a single matching operation, a limit can 1141 be placed on the resources used by a single call to pcre_exec(). The 1142 limit can be changed at run time, as described in the pcreapi documen- 1143 tation. The default is 10 million, but this can be changed by adding a 1144 setting such as 1145 1146 --with-match-limit=500000 1147 1148 to the configure command. This setting has no effect on the 1149 pcre_dfa_exec() matching function. 1150 1151 In some environments it is desirable to limit the depth of recursive 1152 calls of match() more strictly than the total number of calls, in order 1153 to restrict the maximum amount of stack (or heap, if --disable-stack- 1154 for-recursion is specified) that is used. A second limit controls this; 1155 it defaults to the value that is set for --with-match-limit, which 1156 imposes no additional constraints. However, you can set a lower limit 1157 by adding, for example, 1158 1159 --with-match-limit-recursion=10000 1160 1161 to the configure command. This value can also be overridden at run 1162 time. 1163 1164 1165CREATING CHARACTER TABLES AT BUILD TIME 1166 1167 PCRE uses fixed tables for processing characters whose code values are 1168 less than 256. By default, PCRE is built with a set of tables that are 1169 distributed in the file pcre_chartables.c.dist. These tables are for 1170 ASCII codes only. If you add 1171 1172 --enable-rebuild-chartables 1173 1174 to the configure command, the distributed tables are no longer used. 1175 Instead, a program called dftables is compiled and run. This outputs 1176 the source for new set of tables, created in the default locale of your 1177 C run-time system. (This method of replacing the tables does not work 1178 if you are cross compiling, because dftables is run on the local host. 1179 If you need to create alternative tables when cross compiling, you will 1180 have to do so "by hand".) 1181 1182 1183USING EBCDIC CODE 1184 1185 PCRE assumes by default that it will run in an environment where the 1186 character code is ASCII (or Unicode, which is a superset of ASCII). 1187 This is the case for most computer operating systems. PCRE can, how- 1188 ever, be compiled to run in an EBCDIC environment by adding 1189 1190 --enable-ebcdic 1191 1192 to the configure command. This setting implies --enable-rebuild-charta- 1193 bles. You should only use it if you know that you are in an EBCDIC 1194 environment (for example, an IBM mainframe operating system). The 1195 --enable-ebcdic option is incompatible with --enable-utf. 1196 1197 The EBCDIC character that corresponds to an ASCII LF is assumed to have 1198 the value 0x15 by default. However, in some EBCDIC environments, 0x25 1199 is used. In such an environment you should use 1200 1201 --enable-ebcdic-nl25 1202 1203 as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR 1204 has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and 1205 0x25 is not chosen as LF is made to correspond to the Unicode NEL char- 1206 acter (which, in Unicode, is 0x85). 1207 1208 The options that select newline behaviour, such as --enable-newline-is- 1209 cr, and equivalent run-time options, refer to these character values in 1210 an EBCDIC environment. 1211 1212 1213PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT 1214 1215 By default, pcregrep reads all files as plain text. You can build it so 1216 that it recognizes files whose names end in .gz or .bz2, and reads them 1217 with libz or libbz2, respectively, by adding one or both of 1218 1219 --enable-pcregrep-libz 1220 --enable-pcregrep-libbz2 1221 1222 to the configure command. These options naturally require that the rel- 1223 evant libraries are installed on your system. Configuration will fail 1224 if they are not. 1225 1226 1227PCREGREP BUFFER SIZE 1228 1229 pcregrep uses an internal buffer to hold a "window" on the file it is 1230 scanning, in order to be able to output "before" and "after" lines when 1231 it finds a match. The size of the buffer is controlled by a parameter 1232 whose default value is 20K. The buffer itself is three times this size, 1233 but because of the way it is used for holding "before" lines, the long- 1234 est line that is guaranteed to be processable is the parameter size. 1235 You can change the default parameter value by adding, for example, 1236 1237 --with-pcregrep-bufsize=50K 1238 1239 to the configure command. The caller of pcregrep can, however, override 1240 this value by specifying a run-time option. 1241 1242 1243PCRETEST OPTION FOR LIBREADLINE SUPPORT 1244 1245 If you add 1246 1247 --enable-pcretest-libreadline 1248 1249 to the configure command, pcretest is linked with the libreadline 1250 library, and when its input is from a terminal, it reads it using the 1251 readline() function. This provides line-editing and history facilities. 1252 Note that libreadline is GPL-licensed, so if you distribute a binary of 1253 pcretest linked in this way, there may be licensing issues. 1254 1255 Setting this option causes the -lreadline option to be added to the 1256 pcretest build. In many operating environments with a sytem-installed 1257 libreadline this is sufficient. However, in some environments (e.g. if 1258 an unmodified distribution version of readline is in use), some extra 1259 configuration may be necessary. The INSTALL file for libreadline says 1260 this: 1261 1262 "Readline uses the termcap functions, but does not link with the 1263 termcap or curses library itself, allowing applications which link 1264 with readline the to choose an appropriate library." 1265 1266 If your environment has not been set up so that an appropriate library 1267 is automatically included, you may need to add something like 1268 1269 LIBS="-ncurses" 1270 1271 immediately before the configure command. 1272 1273 1274DEBUGGING WITH VALGRIND SUPPORT 1275 1276 By adding the 1277 1278 --enable-valgrind 1279 1280 option to to the configure command, PCRE will use valgrind annotations 1281 to mark certain memory regions as unaddressable. This allows it to 1282 detect invalid memory accesses, and is mostly useful for debugging PCRE 1283 itself. 1284 1285 1286CODE COVERAGE REPORTING 1287 1288 If your C compiler is gcc, you can build a version of PCRE that can 1289 generate a code coverage report for its test suite. To enable this, you 1290 must install lcov version 1.6 or above. Then specify 1291 1292 --enable-coverage 1293 1294 to the configure command and build PCRE in the usual way. 1295 1296 Note that using ccache (a caching C compiler) is incompatible with code 1297 coverage reporting. If you have configured ccache to run automatically 1298 on your system, you must set the environment variable 1299 1300 CCACHE_DISABLE=1 1301 1302 before running make to build PCRE, so that ccache is not used. 1303 1304 When --enable-coverage is used, the following addition targets are 1305 added to the Makefile: 1306 1307 make coverage 1308 1309 This creates a fresh coverage report for the PCRE test suite. It is 1310 equivalent to running "make coverage-reset", "make coverage-baseline", 1311 "make check", and then "make coverage-report". 1312 1313 make coverage-reset 1314 1315 This zeroes the coverage counters, but does nothing else. 1316 1317 make coverage-baseline 1318 1319 This captures baseline coverage information. 1320 1321 make coverage-report 1322 1323 This creates the coverage report. 1324 1325 make coverage-clean-report 1326 1327 This removes the generated coverage report without cleaning the cover- 1328 age data itself. 1329 1330 make coverage-clean-data 1331 1332 This removes the captured coverage data without removing the coverage 1333 files created at compile time (*.gcno). 1334 1335 make coverage-clean 1336 1337 This cleans all coverage data including the generated coverage report. 1338 For more information about code coverage, see the gcov and lcov docu- 1339 mentation. 1340 1341 1342SEE ALSO 1343 1344 pcreapi(3), pcre16, pcre32, pcre_config(3). 1345 1346 1347AUTHOR 1348 1349 Philip Hazel 1350 University Computing Service 1351 Cambridge CB2 3QH, England. 1352 1353 1354REVISION 1355 1356 Last updated: 12 May 2013 1357 Copyright (c) 1997-2013 University of Cambridge. 1358------------------------------------------------------------------------------ 1359 1360 1361PCREMATCHING(3) Library Functions Manual PCREMATCHING(3) 1362 1363 1364 1365NAME 1366 PCRE - Perl-compatible regular expressions 1367 1368PCRE MATCHING ALGORITHMS 1369 1370 This document describes the two different algorithms that are available 1371 in PCRE for matching a compiled regular expression against a given sub- 1372 ject string. The "standard" algorithm is the one provided by the 1373 pcre_exec(), pcre16_exec() and pcre32_exec() functions. These work in 1374 the same as as Perl's matching function, and provide a Perl-compatible 1375 matching operation. The just-in-time (JIT) optimization that is 1376 described in the pcrejit documentation is compatible with these func- 1377 tions. 1378 1379 An alternative algorithm is provided by the pcre_dfa_exec(), 1380 pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a 1381 different way, and are not Perl-compatible. This alternative has advan- 1382 tages and disadvantages compared with the standard algorithm, and these 1383 are described below. 1384 1385 When there is only one possible way in which a given subject string can 1386 match a pattern, the two algorithms give the same answer. A difference 1387 arises, however, when there are multiple possibilities. For example, if 1388 the pattern 1389 1390 ^<.*> 1391 1392 is matched against the string 1393 1394 <something> <something else> <something further> 1395 1396 there are three possible answers. The standard algorithm finds only one 1397 of them, whereas the alternative algorithm finds all three. 1398 1399 1400REGULAR EXPRESSIONS AS TREES 1401 1402 The set of strings that are matched by a regular expression can be rep- 1403 resented as a tree structure. An unlimited repetition in the pattern 1404 makes the tree of infinite size, but it is still a tree. Matching the 1405 pattern to a given subject string (from a given starting point) can be 1406 thought of as a search of the tree. There are two ways to search a 1407 tree: depth-first and breadth-first, and these correspond to the two 1408 matching algorithms provided by PCRE. 1409 1410 1411THE STANDARD MATCHING ALGORITHM 1412 1413 In the terminology of Jeffrey Friedl's book "Mastering Regular Expres- 1414 sions", the standard algorithm is an "NFA algorithm". It conducts a 1415 depth-first search of the pattern tree. That is, it proceeds along a 1416 single path through the tree, checking that the subject matches what is 1417 required. When there is a mismatch, the algorithm tries any alterna- 1418 tives at the current point, and if they all fail, it backs up to the 1419 previous branch point in the tree, and tries the next alternative 1420 branch at that level. This often involves backing up (moving to the 1421 left) in the subject string as well. The order in which repetition 1422 branches are tried is controlled by the greedy or ungreedy nature of 1423 the quantifier. 1424 1425 If a leaf node is reached, a matching string has been found, and at 1426 that point the algorithm stops. Thus, if there is more than one possi- 1427 ble match, this algorithm returns the first one that it finds. Whether 1428 this is the shortest, the longest, or some intermediate length depends 1429 on the way the greedy and ungreedy repetition quantifiers are specified 1430 in the pattern. 1431 1432 Because it ends up with a single path through the tree, it is rela- 1433 tively straightforward for this algorithm to keep track of the sub- 1434 strings that are matched by portions of the pattern in parentheses. 1435 This provides support for capturing parentheses and back references. 1436 1437 1438THE ALTERNATIVE MATCHING ALGORITHM 1439 1440 This algorithm conducts a breadth-first search of the tree. Starting 1441 from the first matching point in the subject, it scans the subject 1442 string from left to right, once, character by character, and as it does 1443 this, it remembers all the paths through the tree that represent valid 1444 matches. In Friedl's terminology, this is a kind of "DFA algorithm", 1445 though it is not implemented as a traditional finite state machine (it 1446 keeps multiple states active simultaneously). 1447 1448 Although the general principle of this matching algorithm is that it 1449 scans the subject string only once, without backtracking, there is one 1450 exception: when a lookaround assertion is encountered, the characters 1451 following or preceding the current point have to be independently 1452 inspected. 1453 1454 The scan continues until either the end of the subject is reached, or 1455 there are no more unterminated paths. At this point, terminated paths 1456 represent the different matching possibilities (if there are none, the 1457 match has failed). Thus, if there is more than one possible match, 1458 this algorithm finds all of them, and in particular, it finds the long- 1459 est. The matches are returned in decreasing order of length. There is 1460 an option to stop the algorithm after the first match (which is neces- 1461 sarily the shortest) is found. 1462 1463 Note that all the matches that are found start at the same point in the 1464 subject. If the pattern 1465 1466 cat(er(pillar)?)? 1467 1468 is matched against the string "the caterpillar catchment", the result 1469 will be the three strings "caterpillar", "cater", and "cat" that start 1470 at the fifth character of the subject. The algorithm does not automati- 1471 cally move on to find matches that start at later positions. 1472 1473 PCRE's "auto-possessification" optimization usually applies to charac- 1474 ter repeats at the end of a pattern (as well as internally). For exam- 1475 ple, the pattern "a\d+" is compiled as if it were "a\d++" because there 1476 is no point even considering the possibility of backtracking into the 1477 repeated digits. For DFA matching, this means that only one possible 1478 match is found. If you really do want multiple matches in such cases, 1479 either use an ungreedy repeat ("a\d+?") or set the PCRE_NO_AUTO_POSSESS 1480 option when compiling. 1481 1482 There are a number of features of PCRE regular expressions that are not 1483 supported by the alternative matching algorithm. They are as follows: 1484 1485 1. Because the algorithm finds all possible matches, the greedy or 1486 ungreedy nature of repetition quantifiers is not relevant. Greedy and 1487 ungreedy quantifiers are treated in exactly the same way. However, pos- 1488 sessive quantifiers can make a difference when what follows could also 1489 match what is quantified, for example in a pattern like this: 1490 1491 ^a++\w! 1492 1493 This pattern matches "aaab!" but not "aaa!", which would be matched by 1494 a non-possessive quantifier. Similarly, if an atomic group is present, 1495 it is matched as if it were a standalone pattern at the current point, 1496 and the longest match is then "locked in" for the rest of the overall 1497 pattern. 1498 1499 2. When dealing with multiple paths through the tree simultaneously, it 1500 is not straightforward to keep track of captured substrings for the 1501 different matching possibilities, and PCRE's implementation of this 1502 algorithm does not attempt to do this. This means that no captured sub- 1503 strings are available. 1504 1505 3. Because no substrings are captured, back references within the pat- 1506 tern are not supported, and cause errors if encountered. 1507 1508 4. For the same reason, conditional expressions that use a backrefer- 1509 ence as the condition or test for a specific group recursion are not 1510 supported. 1511 1512 5. Because many paths through the tree may be active, the \K escape 1513 sequence, which resets the start of the match when encountered (but may 1514 be on some paths and not on others), is not supported. It causes an 1515 error if encountered. 1516 1517 6. Callouts are supported, but the value of the capture_top field is 1518 always 1, and the value of the capture_last field is always -1. 1519 1520 7. The \C escape sequence, which (in the standard algorithm) always 1521 matches a single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is 1522 not supported in these modes, because the alternative algorithm moves 1523 through the subject string one character (not data unit) at a time, for 1524 all active paths through the tree. 1525 1526 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) 1527 are not supported. (*FAIL) is supported, and behaves like a failing 1528 negative assertion. 1529 1530 1531ADVANTAGES OF THE ALTERNATIVE ALGORITHM 1532 1533 Using the alternative matching algorithm provides the following advan- 1534 tages: 1535 1536 1. All possible matches (at a single point in the subject) are automat- 1537 ically found, and in particular, the longest match is found. To find 1538 more than one match using the standard algorithm, you have to do kludgy 1539 things with callouts. 1540 1541 2. Because the alternative algorithm scans the subject string just 1542 once, and never needs to backtrack (except for lookbehinds), it is pos- 1543 sible to pass very long subject strings to the matching function in 1544 several pieces, checking for partial matching each time. Although it is 1545 possible to do multi-segment matching using the standard algorithm by 1546 retaining partially matched substrings, it is more complicated. The 1547 pcrepartial documentation gives details of partial matching and dis- 1548 cusses multi-segment matching. 1549 1550 1551DISADVANTAGES OF THE ALTERNATIVE ALGORITHM 1552 1553 The alternative algorithm suffers from a number of disadvantages: 1554 1555 1. It is substantially slower than the standard algorithm. This is 1556 partly because it has to search for all possible matches, but is also 1557 because it is less susceptible to optimization. 1558 1559 2. Capturing parentheses and back references are not supported. 1560 1561 3. Although atomic groups are supported, their use does not provide the 1562 performance advantage that it does for the standard algorithm. 1563 1564 1565AUTHOR 1566 1567 Philip Hazel 1568 University Computing Service 1569 Cambridge CB2 3QH, England. 1570 1571 1572REVISION 1573 1574 Last updated: 12 November 2013 1575 Copyright (c) 1997-2012 University of Cambridge. 1576------------------------------------------------------------------------------ 1577 1578 1579PCREAPI(3) Library Functions Manual PCREAPI(3) 1580 1581 1582 1583NAME 1584 PCRE - Perl-compatible regular expressions 1585 1586 #include <pcre.h> 1587 1588 1589PCRE NATIVE API BASIC FUNCTIONS 1590 1591 pcre *pcre_compile(const char *pattern, int options, 1592 const char **errptr, int *erroffset, 1593 const unsigned char *tableptr); 1594 1595 pcre *pcre_compile2(const char *pattern, int options, 1596 int *errorcodeptr, 1597 const char **errptr, int *erroffset, 1598 const unsigned char *tableptr); 1599 1600 pcre_extra *pcre_study(const pcre *code, int options, 1601 const char **errptr); 1602 1603 void pcre_free_study(pcre_extra *extra); 1604 1605 int pcre_exec(const pcre *code, const pcre_extra *extra, 1606 const char *subject, int length, int startoffset, 1607 int options, int *ovector, int ovecsize); 1608 1609 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, 1610 const char *subject, int length, int startoffset, 1611 int options, int *ovector, int ovecsize, 1612 int *workspace, int wscount); 1613 1614 1615PCRE NATIVE API STRING EXTRACTION FUNCTIONS 1616 1617 int pcre_copy_named_substring(const pcre *code, 1618 const char *subject, int *ovector, 1619 int stringcount, const char *stringname, 1620 char *buffer, int buffersize); 1621 1622 int pcre_copy_substring(const char *subject, int *ovector, 1623 int stringcount, int stringnumber, char *buffer, 1624 int buffersize); 1625 1626 int pcre_get_named_substring(const pcre *code, 1627 const char *subject, int *ovector, 1628 int stringcount, const char *stringname, 1629 const char **stringptr); 1630 1631 int pcre_get_stringnumber(const pcre *code, 1632 const char *name); 1633 1634 int pcre_get_stringtable_entries(const pcre *code, 1635 const char *name, char **first, char **last); 1636 1637 int pcre_get_substring(const char *subject, int *ovector, 1638 int stringcount, int stringnumber, 1639 const char **stringptr); 1640 1641 int pcre_get_substring_list(const char *subject, 1642 int *ovector, int stringcount, const char ***listptr); 1643 1644 void pcre_free_substring(const char *stringptr); 1645 1646 void pcre_free_substring_list(const char **stringptr); 1647 1648 1649PCRE NATIVE API AUXILIARY FUNCTIONS 1650 1651 int pcre_jit_exec(const pcre *code, const pcre_extra *extra, 1652 const char *subject, int length, int startoffset, 1653 int options, int *ovector, int ovecsize, 1654 pcre_jit_stack *jstack); 1655 1656 pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize); 1657 1658 void pcre_jit_stack_free(pcre_jit_stack *stack); 1659 1660 void pcre_assign_jit_stack(pcre_extra *extra, 1661 pcre_jit_callback callback, void *data); 1662 1663 const unsigned char *pcre_maketables(void); 1664 1665 int pcre_fullinfo(const pcre *code, const pcre_extra *extra, 1666 int what, void *where); 1667 1668 int pcre_refcount(pcre *code, int adjust); 1669 1670 int pcre_config(int what, void *where); 1671 1672 const char *pcre_version(void); 1673 1674 int pcre_pattern_to_host_byte_order(pcre *code, 1675 pcre_extra *extra, const unsigned char *tables); 1676 1677 1678PCRE NATIVE API INDIRECTED FUNCTIONS 1679 1680 void *(*pcre_malloc)(size_t); 1681 1682 void (*pcre_free)(void *); 1683 1684 void *(*pcre_stack_malloc)(size_t); 1685 1686 void (*pcre_stack_free)(void *); 1687 1688 int (*pcre_callout)(pcre_callout_block *); 1689 1690 int (*pcre_stack_guard)(void); 1691 1692 1693PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES 1694 1695 As well as support for 8-bit character strings, PCRE also supports 1696 16-bit strings (from release 8.30) and 32-bit strings (from release 1697 8.32), by means of two additional libraries. They can be built as well 1698 as, or instead of, the 8-bit library. To avoid too much complication, 1699 this document describes the 8-bit versions of the functions, with only 1700 occasional references to the 16-bit and 32-bit libraries. 1701 1702 The 16-bit and 32-bit functions operate in the same way as their 8-bit 1703 counterparts; they just use different data types for their arguments 1704 and results, and their names start with pcre16_ or pcre32_ instead of 1705 pcre_. For every option that has UTF8 in its name (for example, 1706 PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8 1707 replaced by UTF16 or UTF32, respectively. This facility is in fact just 1708 cosmetic; the 16-bit and 32-bit option names define the same bit val- 1709 ues. 1710 1711 References to bytes and UTF-8 in this document should be read as refer- 1712 ences to 16-bit data units and UTF-16 when using the 16-bit library, or 1713 32-bit data units and UTF-32 when using the 32-bit library, unless 1714 specified otherwise. More details of the specific differences for the 1715 16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages. 1716 1717 1718PCRE API OVERVIEW 1719 1720 PCRE has its own native API, which is described in this document. There 1721 are also some wrapper functions (for the 8-bit library only) that cor- 1722 respond to the POSIX regular expression API, but they do not give 1723 access to all the functionality. They are described in the pcreposix 1724 documentation. Both of these APIs define a set of C function calls. A 1725 C++ wrapper (again for the 8-bit library only) is also distributed with 1726 PCRE. It is documented in the pcrecpp page. 1727 1728 The native API C function prototypes are defined in the header file 1729 pcre.h, and on Unix-like systems the (8-bit) library itself is called 1730 libpcre. It can normally be accessed by adding -lpcre to the command 1731 for linking an application that uses PCRE. The header file defines the 1732 macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release 1733 numbers for the library. Applications can use these to include support 1734 for different releases of PCRE. 1735 1736 In a Windows environment, if you want to statically link an application 1737 program against a non-dll pcre.a file, you must define PCRE_STATIC 1738 before including pcre.h or pcrecpp.h, because otherwise the pcre_mal- 1739 loc() and pcre_free() exported functions will be declared 1740 __declspec(dllimport), with unwanted results. 1741 1742 The functions pcre_compile(), pcre_compile2(), pcre_study(), and 1743 pcre_exec() are used for compiling and matching regular expressions in 1744 a Perl-compatible manner. A sample program that demonstrates the sim- 1745 plest way of using them is provided in the file called pcredemo.c in 1746 the PCRE source distribution. A listing of this program is given in the 1747 pcredemo documentation, and the pcresample documentation describes how 1748 to compile and run it. 1749 1750 Just-in-time compiler support is an optional feature of PCRE that can 1751 be built in appropriate hardware environments. It greatly speeds up the 1752 matching performance of many patterns. Simple programs can easily 1753 request that it be used if available, by setting an option that is 1754 ignored when it is not relevant. More complicated programs might need 1755 to make use of the functions pcre_jit_stack_alloc(), 1756 pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control 1757 the JIT code's memory usage. 1758 1759 From release 8.32 there is also a direct interface for JIT execution, 1760 which gives improved performance. The JIT-specific functions are dis- 1761 cussed in the pcrejit documentation. 1762 1763 A second matching function, pcre_dfa_exec(), which is not Perl-compati- 1764 ble, is also provided. This uses a different algorithm for the match- 1765 ing. The alternative algorithm finds all possible matches (at a given 1766 point in the subject), and scans the subject just once (unless there 1767 are lookbehind assertions). However, this algorithm does not return 1768 captured substrings. A description of the two matching algorithms and 1769 their advantages and disadvantages is given in the pcrematching docu- 1770 mentation. 1771 1772 In addition to the main compiling and matching functions, there are 1773 convenience functions for extracting captured substrings from a subject 1774 string that is matched by pcre_exec(). They are: 1775 1776 pcre_copy_substring() 1777 pcre_copy_named_substring() 1778 pcre_get_substring() 1779 pcre_get_named_substring() 1780 pcre_get_substring_list() 1781 pcre_get_stringnumber() 1782 pcre_get_stringtable_entries() 1783 1784 pcre_free_substring() and pcre_free_substring_list() are also provided, 1785 to free the memory used for extracted strings. 1786 1787 The function pcre_maketables() is used to build a set of character 1788 tables in the current locale for passing to pcre_compile(), 1789 pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is 1790 provided for specialist use. Most commonly, no special tables are 1791 passed, in which case internal tables that are generated when PCRE is 1792 built are used. 1793 1794 The function pcre_fullinfo() is used to find out information about a 1795 compiled pattern. The function pcre_version() returns a pointer to a 1796 string containing the version of PCRE and its date of release. 1797 1798 The function pcre_refcount() maintains a reference count in a data 1799 block containing a compiled pattern. This is provided for the benefit 1800 of object-oriented applications. 1801 1802 The global variables pcre_malloc and pcre_free initially contain the 1803 entry points of the standard malloc() and free() functions, respec- 1804 tively. PCRE calls the memory management functions via these variables, 1805 so a calling program can replace them if it wishes to intercept the 1806 calls. This should be done before calling any PCRE functions. 1807 1808 The global variables pcre_stack_malloc and pcre_stack_free are also 1809 indirections to memory management functions. These special functions 1810 are used only when PCRE is compiled to use the heap for remembering 1811 data, instead of recursive function calls, when running the pcre_exec() 1812 function. See the pcrebuild documentation for details of how to do 1813 this. It is a non-standard way of building PCRE, for use in environ- 1814 ments that have limited stacks. Because of the greater use of memory 1815 management, it runs more slowly. Separate functions are provided so 1816 that special-purpose external code can be used for this case. When 1817 used, these functions always allocate memory blocks of the same size. 1818 There is a discussion about PCRE's stack usage in the pcrestack docu- 1819 mentation. 1820 1821 The global variable pcre_callout initially contains NULL. It can be set 1822 by the caller to a "callout" function, which PCRE will then call at 1823 specified points during a matching operation. Details are given in the 1824 pcrecallout documentation. 1825 1826 The global variable pcre_stack_guard initially contains NULL. It can be 1827 set by the caller to a function that is called by PCRE whenever it 1828 starts to compile a parenthesized part of a pattern. When parentheses 1829 are nested, PCRE uses recursive function calls, which use up the system 1830 stack. This function is provided so that applications with restricted 1831 stacks can force a compilation error if the stack runs out. The func- 1832 tion should return zero if all is well, or non-zero to force an error. 1833 1834 1835NEWLINES 1836 1837 PCRE supports five different conventions for indicating line breaks in 1838 strings: a single CR (carriage return) character, a single LF (line- 1839 feed) character, the two-character sequence CRLF, any of the three pre- 1840 ceding, or any Unicode newline sequence. The Unicode newline sequences 1841 are the three just mentioned, plus the single characters VT (vertical 1842 tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line 1843 separator, U+2028), and PS (paragraph separator, U+2029). 1844 1845 Each of the first three conventions is used by at least one operating 1846 system as its standard newline sequence. When PCRE is built, a default 1847 can be specified. The default default is LF, which is the Unix stan- 1848 dard. When PCRE is run, the default can be overridden, either when a 1849 pattern is compiled, or when it is matched. 1850 1851 At compile time, the newline convention can be specified by the options 1852 argument of pcre_compile(), or it can be specified by special text at 1853 the start of the pattern itself; this overrides any other settings. See 1854 the pcrepattern page for details of the special character sequences. 1855 1856 In the PCRE documentation the word "newline" is used to mean "the char- 1857 acter or pair of characters that indicate a line break". The choice of 1858 newline convention affects the handling of the dot, circumflex, and 1859 dollar metacharacters, the handling of #-comments in /x mode, and, when 1860 CRLF is a recognized line ending sequence, the match position advance- 1861 ment for a non-anchored pattern. There is more detail about this in the 1862 section on pcre_exec() options below. 1863 1864 The choice of newline convention does not affect the interpretation of 1865 the \n or \r escape sequences, nor does it affect what \R matches, 1866 which is controlled in a similar way, but by separate options. 1867 1868 1869MULTITHREADING 1870 1871 The PCRE functions can be used in multi-threading applications, with 1872 the proviso that the memory management functions pointed to by 1873 pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the 1874 callout and stack-checking functions pointed to by pcre_callout and 1875 pcre_stack_guard, are shared by all threads. 1876 1877 The compiled form of a regular expression is not altered during match- 1878 ing, so the same compiled pattern can safely be used by several threads 1879 at once. 1880 1881 If the just-in-time optimization feature is being used, it needs sepa- 1882 rate memory stack areas for each thread. See the pcrejit documentation 1883 for more details. 1884 1885 1886SAVING PRECOMPILED PATTERNS FOR LATER USE 1887 1888 The compiled form of a regular expression can be saved and re-used at a 1889 later time, possibly by a different program, and even on a host other 1890 than the one on which it was compiled. Details are given in the 1891 pcreprecompile documentation, which includes a description of the 1892 pcre_pattern_to_host_byte_order() function. However, compiling a regu- 1893 lar expression with one version of PCRE for use with a different ver- 1894 sion is not guaranteed to work and may cause crashes. 1895 1896 1897CHECKING BUILD-TIME OPTIONS 1898 1899 int pcre_config(int what, void *where); 1900 1901 The function pcre_config() makes it possible for a PCRE client to dis- 1902 cover which optional features have been compiled into the PCRE library. 1903 The pcrebuild documentation has more details about these optional fea- 1904 tures. 1905 1906 The first argument for pcre_config() is an integer, specifying which 1907 information is required; the second argument is a pointer to a variable 1908 into which the information is placed. The returned value is zero on 1909 success, or the negative error code PCRE_ERROR_BADOPTION if the value 1910 in the first argument is not recognized. The following information is 1911 available: 1912 1913 PCRE_CONFIG_UTF8 1914 1915 The output is an integer that is set to one if UTF-8 support is avail- 1916 able; otherwise it is set to zero. This value should normally be given 1917 to the 8-bit version of this function, pcre_config(). If it is given to 1918 the 16-bit or 32-bit version of this function, the result is 1919 PCRE_ERROR_BADOPTION. 1920 1921 PCRE_CONFIG_UTF16 1922 1923 The output is an integer that is set to one if UTF-16 support is avail- 1924 able; otherwise it is set to zero. This value should normally be given 1925 to the 16-bit version of this function, pcre16_config(). If it is given 1926 to the 8-bit or 32-bit version of this function, the result is 1927 PCRE_ERROR_BADOPTION. 1928 1929 PCRE_CONFIG_UTF32 1930 1931 The output is an integer that is set to one if UTF-32 support is avail- 1932 able; otherwise it is set to zero. This value should normally be given 1933 to the 32-bit version of this function, pcre32_config(). If it is given 1934 to the 8-bit or 16-bit version of this function, the result is 1935 PCRE_ERROR_BADOPTION. 1936 1937 PCRE_CONFIG_UNICODE_PROPERTIES 1938 1939 The output is an integer that is set to one if support for Unicode 1940 character properties is available; otherwise it is set to zero. 1941 1942 PCRE_CONFIG_JIT 1943 1944 The output is an integer that is set to one if support for just-in-time 1945 compiling is available; otherwise it is set to zero. 1946 1947 PCRE_CONFIG_JITTARGET 1948 1949 The output is a pointer to a zero-terminated "const char *" string. If 1950 JIT support is available, the string contains the name of the architec- 1951 ture for which the JIT compiler is configured, for example "x86 32bit 1952 (little endian + unaligned)". If JIT support is not available, the 1953 result is NULL. 1954 1955 PCRE_CONFIG_NEWLINE 1956 1957 The output is an integer whose value specifies the default character 1958 sequence that is recognized as meaning "newline". The values that are 1959 supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338 1960 for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, 1961 ANYCRLF, and ANY yield the same values. However, the value for LF is 1962 normally 21, though some EBCDIC environments use 37. The corresponding 1963 values for CRLF are 3349 and 3365. The default should normally corre- 1964 spond to the standard sequence for your operating system. 1965 1966 PCRE_CONFIG_BSR 1967 1968 The output is an integer whose value indicates what character sequences 1969 the \R escape sequence matches by default. A value of 0 means that \R 1970 matches any Unicode line ending sequence; a value of 1 means that \R 1971 matches only CR, LF, or CRLF. The default can be overridden when a pat- 1972 tern is compiled or matched. 1973 1974 PCRE_CONFIG_LINK_SIZE 1975 1976 The output is an integer that contains the number of bytes used for 1977 internal linkage in compiled regular expressions. For the 8-bit 1978 library, the value can be 2, 3, or 4. For the 16-bit library, the value 1979 is either 2 or 4 and is still a number of bytes. For the 32-bit 1980 library, the value is either 2 or 4 and is still a number of bytes. The 1981 default value of 2 is sufficient for all but the most massive patterns, 1982 since it allows the compiled pattern to be up to 64K in size. Larger 1983 values allow larger regular expressions to be compiled, at the expense 1984 of slower matching. 1985 1986 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD 1987 1988 The output is an integer that contains the threshold above which the 1989 POSIX interface uses malloc() for output vectors. Further details are 1990 given in the pcreposix documentation. 1991 1992 PCRE_CONFIG_PARENS_LIMIT 1993 1994 The output is a long integer that gives the maximum depth of nesting of 1995 parentheses (of any kind) in a pattern. This limit is imposed to cap 1996 the amount of system stack used when a pattern is compiled. It is spec- 1997 ified when PCRE is built; the default is 250. This limit does not take 1998 into account the stack that may already be used by the calling applica- 1999 tion. For finer control over compilation stack usage, you can set a 2000 pointer to an external checking function in pcre_stack_guard. 2001 2002 PCRE_CONFIG_MATCH_LIMIT 2003 2004 The output is a long integer that gives the default limit for the num- 2005 ber of internal matching function calls in a pcre_exec() execution. 2006 Further details are given with pcre_exec() below. 2007 2008 PCRE_CONFIG_MATCH_LIMIT_RECURSION 2009 2010 The output is a long integer that gives the default limit for the depth 2011 of recursion when calling the internal matching function in a 2012 pcre_exec() execution. Further details are given with pcre_exec() 2013 below. 2014 2015 PCRE_CONFIG_STACKRECURSE 2016 2017 The output is an integer that is set to one if internal recursion when 2018 running pcre_exec() is implemented by recursive function calls that use 2019 the stack to remember their state. This is the usual way that PCRE is 2020 compiled. The output is zero if PCRE was compiled to use blocks of data 2021 on the heap instead of recursive function calls. In this case, 2022 pcre_stack_malloc and pcre_stack_free are called to manage memory 2023 blocks on the heap, thus avoiding the use of the stack. 2024 2025 2026COMPILING A PATTERN 2027 2028 pcre *pcre_compile(const char *pattern, int options, 2029 const char **errptr, int *erroffset, 2030 const unsigned char *tableptr); 2031 2032 pcre *pcre_compile2(const char *pattern, int options, 2033 int *errorcodeptr, 2034 const char **errptr, int *erroffset, 2035 const unsigned char *tableptr); 2036 2037 Either of the functions pcre_compile() or pcre_compile2() can be called 2038 to compile a pattern into an internal form. The only difference between 2039 the two interfaces is that pcre_compile2() has an additional argument, 2040 errorcodeptr, via which a numerical error code can be returned. To 2041 avoid too much repetition, we refer just to pcre_compile() below, but 2042 the information applies equally to pcre_compile2(). 2043 2044 The pattern is a C string terminated by a binary zero, and is passed in 2045 the pattern argument. A pointer to a single block of memory that is 2046 obtained via pcre_malloc is returned. This contains the compiled code 2047 and related data. The pcre type is defined for the returned block; this 2048 is a typedef for a structure whose contents are not externally defined. 2049 It is up to the caller to free the memory (via pcre_free) when it is no 2050 longer required. 2051 2052 Although the compiled code of a PCRE regex is relocatable, that is, it 2053 does not depend on memory location, the complete pcre data block is not 2054 fully relocatable, because it may contain a copy of the tableptr argu- 2055 ment, which is an address (see below). 2056 2057 The options argument contains various bit settings that affect the com- 2058 pilation. It should be zero if no options are required. The available 2059 options are described below. Some of them (in particular, those that 2060 are compatible with Perl, but some others as well) can also be set and 2061 unset from within the pattern (see the detailed description in the 2062 pcrepattern documentation). For those options that can be different in 2063 different parts of the pattern, the contents of the options argument 2064 specifies their settings at the start of compilation and execution. The 2065 PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and 2066 PCRE_NO_START_OPTIMIZE options can be set at the time of matching as 2067 well as at compile time. 2068 2069 If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise, 2070 if compilation of a pattern fails, pcre_compile() returns NULL, and 2071 sets the variable pointed to by errptr to point to a textual error mes- 2072 sage. This is a static string that is part of the library. You must not 2073 try to free it. Normally, the offset from the start of the pattern to 2074 the data unit that was being processed when the error was discovered is 2075 placed in the variable pointed to by erroffset, which must not be NULL 2076 (if it is, an immediate error is given). However, for an invalid UTF-8 2077 or UTF-16 string, the offset is that of the first data unit of the 2078 failing character. 2079 2080 Some errors are not detected until the whole pattern has been scanned; 2081 in these cases, the offset passed back is the length of the pattern. 2082 Note that the offset is in data units, not characters, even in a UTF 2083 mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char- 2084 acter. 2085 2086 If pcre_compile2() is used instead of pcre_compile(), and the error- 2087 codeptr argument is not NULL, a non-zero error code number is returned 2088 via this argument in the event of an error. This is in addition to the 2089 textual error message. Error codes and messages are listed below. 2090 2091 If the final argument, tableptr, is NULL, PCRE uses a default set of 2092 character tables that are built when PCRE is compiled, using the 2093 default C locale. Otherwise, tableptr must be an address that is the 2094 result of a call to pcre_maketables(). This value is stored with the 2095 compiled pattern, and used again by pcre_exec() and pcre_dfa_exec() 2096 when the pattern is matched. For more discussion, see the section on 2097 locale support below. 2098 2099 This code fragment shows a typical straightforward call to pcre_com- 2100 pile(): 2101 2102 pcre *re; 2103 const char *error; 2104 int erroffset; 2105 re = pcre_compile( 2106 "^A.*Z", /* the pattern */ 2107 0, /* default options */ 2108 &error, /* for error message */ 2109 &erroffset, /* for error offset */ 2110 NULL); /* use default character tables */ 2111 2112 The following names for option bits are defined in the pcre.h header 2113 file: 2114 2115 PCRE_ANCHORED 2116 2117 If this bit is set, the pattern is forced to be "anchored", that is, it 2118 is constrained to match only at the first matching point in the string 2119 that is being searched (the "subject string"). This effect can also be 2120 achieved by appropriate constructs in the pattern itself, which is the 2121 only way to do it in Perl. 2122 2123 PCRE_AUTO_CALLOUT 2124 2125 If this bit is set, pcre_compile() automatically inserts callout items, 2126 all with number 255, before each pattern item. For discussion of the 2127 callout facility, see the pcrecallout documentation. 2128 2129 PCRE_BSR_ANYCRLF 2130 PCRE_BSR_UNICODE 2131 2132 These options (which are mutually exclusive) control what the \R escape 2133 sequence matches. The choice is either to match only CR, LF, or CRLF, 2134 or to match any Unicode newline sequence. The default is specified when 2135 PCRE is built. It can be overridden from within the pattern, or by set- 2136 ting an option when a compiled pattern is matched. 2137 2138 PCRE_CASELESS 2139 2140 If this bit is set, letters in the pattern match both upper and lower 2141 case letters. It is equivalent to Perl's /i option, and it can be 2142 changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE 2143 always understands the concept of case for characters whose values are 2144 less than 128, so caseless matching is always possible. For characters 2145 with higher values, the concept of case is supported if PCRE is com- 2146 piled with Unicode property support, but not otherwise. If you want to 2147 use caseless matching for characters 128 and above, you must ensure 2148 that PCRE is compiled with Unicode property support as well as with 2149 UTF-8 support. 2150 2151 PCRE_DOLLAR_ENDONLY 2152 2153 If this bit is set, a dollar metacharacter in the pattern matches only 2154 at the end of the subject string. Without this option, a dollar also 2155 matches immediately before a newline at the end of the string (but not 2156 before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored 2157 if PCRE_MULTILINE is set. There is no equivalent to this option in 2158 Perl, and no way to set it within a pattern. 2159 2160 PCRE_DOTALL 2161 2162 If this bit is set, a dot metacharacter in the pattern matches a char- 2163 acter of any value, including one that indicates a newline. However, it 2164 only ever matches one character, even if newlines are coded as CRLF. 2165 Without this option, a dot does not match when the current position is 2166 at a newline. This option is equivalent to Perl's /s option, and it can 2167 be changed within a pattern by a (?s) option setting. A negative class 2168 such as [^a] always matches newline characters, independent of the set- 2169 ting of this option. 2170 2171 PCRE_DUPNAMES 2172 2173 If this bit is set, names used to identify capturing subpatterns need 2174 not be unique. This can be helpful for certain types of pattern when it 2175 is known that only one instance of the named subpattern can ever be 2176 matched. There are more details of named subpatterns below; see also 2177 the pcrepattern documentation. 2178 2179 PCRE_EXTENDED 2180 2181 If this bit is set, most white space characters in the pattern are 2182 totally ignored except when escaped or inside a character class. How- 2183 ever, white space is not allowed within sequences such as (?> that 2184 introduce various parenthesized subpatterns, nor within a numerical 2185 quantifier such as {1,3}. However, ignorable white space is permitted 2186 between an item and a following quantifier and between a quantifier and 2187 a following + that indicates possessiveness. 2188 2189 White space did not used to include the VT character (code 11), because 2190 Perl did not treat this character as white space. However, Perl changed 2191 at release 5.18, so PCRE followed at release 8.34, and VT is now 2192 treated as white space. 2193 2194 PCRE_EXTENDED also causes characters between an unescaped # outside a 2195 character class and the next newline, inclusive, to be ignored. 2196 PCRE_EXTENDED is equivalent to Perl's /x option, and it can be changed 2197 within a pattern by a (?x) option setting. 2198 2199 Which characters are interpreted as newlines is controlled by the 2200 options passed to pcre_compile() or by a special sequence at the start 2201 of the pattern, as described in the section entitled "Newline conven- 2202 tions" in the pcrepattern documentation. Note that the end of this type 2203 of comment is a literal newline sequence in the pattern; escape 2204 sequences that happen to represent a newline do not count. 2205 2206 This option makes it possible to include comments inside complicated 2207 patterns. Note, however, that this applies only to data characters. 2208 White space characters may never appear within special character 2209 sequences in a pattern, for example within the sequence (?( that intro- 2210 duces a conditional subpattern. 2211 2212 PCRE_EXTRA 2213 2214 This option was invented in order to turn on additional functionality 2215 of PCRE that is incompatible with Perl, but it is currently of very 2216 little use. When set, any backslash in a pattern that is followed by a 2217 letter that has no special meaning causes an error, thus reserving 2218 these combinations for future expansion. By default, as in Perl, a 2219 backslash followed by a letter with no special meaning is treated as a 2220 literal. (Perl can, however, be persuaded to give an error for this, by 2221 running it with the -w option.) There are at present no other features 2222 controlled by this option. It can also be set by a (?X) option setting 2223 within a pattern. 2224 2225 PCRE_FIRSTLINE 2226 2227 If this option is set, an unanchored pattern is required to match 2228 before or at the first newline in the subject string, though the 2229 matched text may continue over the newline. 2230 2231 PCRE_JAVASCRIPT_COMPAT 2232 2233 If this option is set, PCRE's behaviour is changed in some ways so that 2234 it is compatible with JavaScript rather than Perl. The changes are as 2235 follows: 2236 2237 (1) A lone closing square bracket in a pattern causes a compile-time 2238 error, because this is illegal in JavaScript (by default it is treated 2239 as a data character). Thus, the pattern AB]CD becomes illegal when this 2240 option is set. 2241 2242 (2) At run time, a back reference to an unset subpattern group matches 2243 an empty string (by default this causes the current matching alterna- 2244 tive to fail). A pattern such as (\1)(a) succeeds when this option is 2245 set (assuming it can find an "a" in the subject), whereas it fails by 2246 default, for Perl compatibility. 2247 2248 (3) \U matches an upper case "U" character; by default \U causes a com- 2249 pile time error (Perl uses \U to upper case subsequent characters). 2250 2251 (4) \u matches a lower case "u" character unless it is followed by four 2252 hexadecimal digits, in which case the hexadecimal number defines the 2253 code point to match. By default, \u causes a compile time error (Perl 2254 uses it to upper case the following character). 2255 2256 (5) \x matches a lower case "x" character unless it is followed by two 2257 hexadecimal digits, in which case the hexadecimal number defines the 2258 code point to match. By default, as in Perl, a hexadecimal number is 2259 always expected after \x, but it may have zero, one, or two digits (so, 2260 for example, \xz matches a binary zero character followed by z). 2261 2262 PCRE_MULTILINE 2263 2264 By default, for the purposes of matching "start of line" and "end of 2265 line", PCRE treats the subject string as consisting of a single line of 2266 characters, even if it actually contains newlines. The "start of line" 2267 metacharacter (^) matches only at the start of the string, and the "end 2268 of line" metacharacter ($) matches only at the end of the string, or 2269 before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set). 2270 Note, however, that unless PCRE_DOTALL is set, the "any character" 2271 metacharacter (.) does not match at a newline. This behaviour (for ^, 2272 $, and dot) is the same as Perl. 2273 2274 When PCRE_MULTILINE it is set, the "start of line" and "end of line" 2275 constructs match immediately following or immediately before internal 2276 newlines in the subject string, respectively, as well as at the very 2277 start and end. This is equivalent to Perl's /m option, and it can be 2278 changed within a pattern by a (?m) option setting. If there are no new- 2279 lines in a subject string, or no occurrences of ^ or $ in a pattern, 2280 setting PCRE_MULTILINE has no effect. 2281 2282 PCRE_NEVER_UTF 2283 2284 This option locks out interpretation of the pattern as UTF-8 (or UTF-16 2285 or UTF-32 in the 16-bit and 32-bit libraries). In particular, it pre- 2286 vents the creator of the pattern from switching to UTF interpretation 2287 by starting the pattern with (*UTF). This may be useful in applications 2288 that process patterns from external sources. The combination of 2289 PCRE_UTF8 and PCRE_NEVER_UTF also causes an error. 2290 2291 PCRE_NEWLINE_CR 2292 PCRE_NEWLINE_LF 2293 PCRE_NEWLINE_CRLF 2294 PCRE_NEWLINE_ANYCRLF 2295 PCRE_NEWLINE_ANY 2296 2297 These options override the default newline definition that was chosen 2298 when PCRE was built. Setting the first or the second specifies that a 2299 newline is indicated by a single character (CR or LF, respectively). 2300 Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the 2301 two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies 2302 that any of the three preceding sequences should be recognized. Setting 2303 PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be 2304 recognized. 2305 2306 In an ASCII/Unicode environment, the Unicode newline sequences are the 2307 three just mentioned, plus the single characters VT (vertical tab, 2308 U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep- 2309 arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit 2310 library, the last two are recognized only in UTF-8 mode. 2311 2312 When PCRE is compiled to run in an EBCDIC (mainframe) environment, the 2313 code for CR is 0x0d, the same as ASCII. However, the character code for 2314 LF is normally 0x15, though in some EBCDIC environments 0x25 is used. 2315 Whichever of these is not LF is made to correspond to Unicode's NEL 2316 character. EBCDIC codes are all less than 256. For more details, see 2317 the pcrebuild documentation. 2318 2319 The newline setting in the options word uses three bits that are 2320 treated as a number, giving eight possibilities. Currently only six are 2321 used (default plus the five values above). This means that if you set 2322 more than one newline option, the combination may or may not be sensi- 2323 ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to 2324 PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and 2325 cause an error. 2326 2327 The only time that a line break in a pattern is specially recognized 2328 when compiling is when PCRE_EXTENDED is set. CR and LF are white space 2329 characters, and so are ignored in this mode. Also, an unescaped # out- 2330 side a character class indicates a comment that lasts until after the 2331 next line break sequence. In other circumstances, line break sequences 2332 in patterns are treated as literal data. 2333 2334 The newline option that is set at compile time becomes the default that 2335 is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden. 2336 2337 PCRE_NO_AUTO_CAPTURE 2338 2339 If this option is set, it disables the use of numbered capturing paren- 2340 theses in the pattern. Any opening parenthesis that is not followed by 2341 ? behaves as if it were followed by ?: but named parentheses can still 2342 be used for capturing (and they acquire numbers in the usual way). 2343 There is no equivalent of this option in Perl. 2344 2345 PCRE_NO_AUTO_POSSESS 2346 2347 If this option is set, it disables "auto-possessification". This is an 2348 optimization that, for example, turns a+b into a++b in order to avoid 2349 backtracks into a+ that can never be successful. However, if callouts 2350 are in use, auto-possessification means that some of them are never 2351 taken. You can set this option if you want the matching functions to do 2352 a full unoptimized search and run all the callouts, but it is mainly 2353 provided for testing purposes. 2354 2355 PCRE_NO_START_OPTIMIZE 2356 2357 This is an option that acts at matching time; that is, it is really an 2358 option for pcre_exec() or pcre_dfa_exec(). If it is set at compile 2359 time, it is remembered with the compiled pattern and assumed at match- 2360 ing time. This is necessary if you want to use JIT execution, because 2361 the JIT compiler needs to know whether or not this option is set. For 2362 details see the discussion of PCRE_NO_START_OPTIMIZE below. 2363 2364 PCRE_UCP 2365 2366 This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W, 2367 \w, and some of the POSIX character classes. By default, only ASCII 2368 characters are recognized, but if PCRE_UCP is set, Unicode properties 2369 are used instead to classify characters. More details are given in the 2370 section on generic character types in the pcrepattern page. If you set 2371 PCRE_UCP, matching one of the items it affects takes much longer. The 2372 option is available only if PCRE has been compiled with Unicode prop- 2373 erty support. 2374 2375 PCRE_UNGREEDY 2376 2377 This option inverts the "greediness" of the quantifiers so that they 2378 are not greedy by default, but become greedy if followed by "?". It is 2379 not compatible with Perl. It can also be set by a (?U) option setting 2380 within the pattern. 2381 2382 PCRE_UTF8 2383 2384 This option causes PCRE to regard both the pattern and the subject as 2385 strings of UTF-8 characters instead of single-byte strings. However, it 2386 is available only when PCRE is built to include UTF support. If not, 2387 the use of this option provokes an error. Details of how this option 2388 changes the behaviour of PCRE are given in the pcreunicode page. 2389 2390 PCRE_NO_UTF8_CHECK 2391 2392 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is 2393 automatically checked. There is a discussion about the validity of 2394 UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is 2395 found, pcre_compile() returns an error. If you already know that your 2396 pattern is valid, and you want to skip this check for performance rea- 2397 sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the 2398 effect of passing an invalid UTF-8 string as a pattern is undefined. It 2399 may cause your program to crash or loop. Note that this option can also 2400 be passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity 2401 checking of subject strings only. If the same string is being matched 2402 many times, the option can be safely set for the second and subsequent 2403 matchings to improve performance. 2404 2405 2406COMPILATION ERROR CODES 2407 2408 The following table lists the error codes than may be returned by 2409 pcre_compile2(), along with the error messages that may be returned by 2410 both compiling functions. Note that error messages are always 8-bit 2411 ASCII strings, even in 16-bit or 32-bit mode. As PCRE has developed, 2412 some error codes have fallen out of use. To avoid confusion, they have 2413 not been re-used. 2414 2415 0 no error 2416 1 \ at end of pattern 2417 2 \c at end of pattern 2418 3 unrecognized character follows \ 2419 4 numbers out of order in {} quantifier 2420 5 number too big in {} quantifier 2421 6 missing terminating ] for character class 2422 7 invalid escape sequence in character class 2423 8 range out of order in character class 2424 9 nothing to repeat 2425 10 [this code is not in use] 2426 11 internal error: unexpected repeat 2427 12 unrecognized character after (? or (?- 2428 13 POSIX named classes are supported only within a class 2429 14 missing ) 2430 15 reference to non-existent subpattern 2431 16 erroffset passed as NULL 2432 17 unknown option bit(s) set 2433 18 missing ) after comment 2434 19 [this code is not in use] 2435 20 regular expression is too large 2436 21 failed to get memory 2437 22 unmatched parentheses 2438 23 internal error: code overflow 2439 24 unrecognized character after (?< 2440 25 lookbehind assertion is not fixed length 2441 26 malformed number or name after (?( 2442 27 conditional group contains more than two branches 2443 28 assertion expected after (?( 2444 29 (?R or (?[+-]digits must be followed by ) 2445 30 unknown POSIX class name 2446 31 POSIX collating elements are not supported 2447 32 this version of PCRE is compiled without UTF support 2448 33 [this code is not in use] 2449 34 character value in \x{} or \o{} is too large 2450 35 invalid condition (?(0) 2451 36 \C not allowed in lookbehind assertion 2452 37 PCRE does not support \L, \l, \N{name}, \U, or \u 2453 38 number after (?C is > 255 2454 39 closing ) for (?C expected 2455 40 recursive call could loop indefinitely 2456 41 unrecognized character after (?P 2457 42 syntax error in subpattern name (missing terminator) 2458 43 two named subpatterns have the same name 2459 44 invalid UTF-8 string (specifically UTF-8) 2460 45 support for \P, \p, and \X has not been compiled 2461 46 malformed \P or \p sequence 2462 47 unknown property name after \P or \p 2463 48 subpattern name is too long (maximum 32 characters) 2464 49 too many named subpatterns (maximum 10000) 2465 50 [this code is not in use] 2466 51 octal value is greater than \377 in 8-bit non-UTF-8 mode 2467 52 internal error: overran compiling workspace 2468 53 internal error: previously-checked referenced subpattern 2469 not found 2470 54 DEFINE group contains more than one branch 2471 55 repeating a DEFINE group is not allowed 2472 56 inconsistent NEWLINE options 2473 57 \g is not followed by a braced, angle-bracketed, or quoted 2474 name/number or by a plain number 2475 58 a numbered reference must not be zero 2476 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT) 2477 60 (*VERB) not recognized or malformed 2478 61 number is too big 2479 62 subpattern name expected 2480 63 digit expected after (?+ 2481 64 ] is an invalid data character in JavaScript compatibility mode 2482 65 different names for subpatterns of the same number are 2483 not allowed 2484 66 (*MARK) must have an argument 2485 67 this version of PCRE is not compiled with Unicode property 2486 support 2487 68 \c must be followed by an ASCII character 2488 69 \k is not followed by a braced, angle-bracketed, or quoted name 2489 70 internal error: unknown opcode in find_fixedlength() 2490 71 \N is not supported in a class 2491 72 too many forward references 2492 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff) 2493 74 invalid UTF-16 string (specifically UTF-16) 2494 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN) 2495 76 character value in \u.... sequence is too large 2496 77 invalid UTF-32 string (specifically UTF-32) 2497 78 setting UTF is disabled by the application 2498 79 non-hex character in \x{} (closing brace missing?) 2499 80 non-octal character in \o{} (closing brace missing?) 2500 81 missing opening brace after \o 2501 82 parentheses are too deeply nested 2502 83 invalid range in character class 2503 84 group name must start with a non-digit 2504 85 parentheses are too deeply nested (stack check) 2505 2506 The numbers 32 and 10000 in errors 48 and 49 are defaults; different 2507 values may be used if the limits were changed when PCRE was built. 2508 2509 2510STUDYING A PATTERN 2511 2512 pcre_extra *pcre_study(const pcre *code, int options, 2513 const char **errptr); 2514 2515 If a compiled pattern is going to be used several times, it is worth 2516 spending more time analyzing it in order to speed up the time taken for 2517 matching. The function pcre_study() takes a pointer to a compiled pat- 2518 tern as its first argument. If studying the pattern produces additional 2519 information that will help speed up matching, pcre_study() returns a 2520 pointer to a pcre_extra block, in which the study_data field points to 2521 the results of the study. 2522 2523 The returned value from pcre_study() can be passed directly to 2524 pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con- 2525 tains other fields that can be set by the caller before the block is 2526 passed; these are described below in the section on matching a pattern. 2527 2528 If studying the pattern does not produce any useful information, 2529 pcre_study() returns NULL by default. In that circumstance, if the 2530 calling program wants to pass any of the other fields to pcre_exec() or 2531 pcre_dfa_exec(), it must set up its own pcre_extra block. However, if 2532 pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it 2533 returns a pcre_extra block even if studying did not find any additional 2534 information. It may still return NULL, however, if an error occurs in 2535 pcre_study(). 2536 2537 The second argument of pcre_study() contains option bits. There are 2538 three further options in addition to PCRE_STUDY_EXTRA_NEEDED: 2539 2540 PCRE_STUDY_JIT_COMPILE 2541 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE 2542 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE 2543 2544 If any of these are set, and the just-in-time compiler is available, 2545 the pattern is further compiled into machine code that executes much 2546 faster than the pcre_exec() interpretive matching function. If the 2547 just-in-time compiler is not available, these options are ignored. All 2548 undefined bits in the options argument must be zero. 2549 2550 JIT compilation is a heavyweight optimization. It can take some time 2551 for patterns to be analyzed, and for one-off matches and simple pat- 2552 terns the benefit of faster execution might be offset by a much slower 2553 study time. Not all patterns can be optimized by the JIT compiler. For 2554 those that cannot be handled, matching automatically falls back to the 2555 pcre_exec() interpreter. For more details, see the pcrejit documenta- 2556 tion. 2557 2558 The third argument for pcre_study() is a pointer for an error message. 2559 If studying succeeds (even if no data is returned), the variable it 2560 points to is set to NULL. Otherwise it is set to point to a textual 2561 error message. This is a static string that is part of the library. You 2562 must not try to free it. You should test the error pointer for NULL 2563 after calling pcre_study(), to be sure that it has run successfully. 2564 2565 When you are finished with a pattern, you can free the memory used for 2566 the study data by calling pcre_free_study(). This function was added to 2567 the API for release 8.20. For earlier versions, the memory could be 2568 freed with pcre_free(), just like the pattern itself. This will still 2569 work in cases where JIT optimization is not used, but it is advisable 2570 to change to the new function when convenient. 2571 2572 This is a typical way in which pcre_study() is used (except that in a 2573 real application there should be tests for errors): 2574 2575 int rc; 2576 pcre *re; 2577 pcre_extra *sd; 2578 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL); 2579 sd = pcre_study( 2580 re, /* result of pcre_compile() */ 2581 0, /* no options */ 2582 &error); /* set to NULL or points to a message */ 2583 rc = pcre_exec( /* see below for details of pcre_exec() options */ 2584 re, sd, "subject", 7, 0, 0, ovector, 30); 2585 ... 2586 pcre_free_study(sd); 2587 pcre_free(re); 2588 2589 Studying a pattern does two things: first, a lower bound for the length 2590 of subject string that is needed to match the pattern is computed. This 2591 does not mean that there are any strings of that length that match, but 2592 it does guarantee that no shorter strings match. The value is used to 2593 avoid wasting time by trying to match strings that are shorter than the 2594 lower bound. You can find out the value in a calling program via the 2595 pcre_fullinfo() function. 2596 2597 Studying a pattern is also useful for non-anchored patterns that do not 2598 have a single fixed starting character. A bitmap of possible starting 2599 bytes is created. This speeds up finding a position in the subject at 2600 which to start matching. (In 16-bit mode, the bitmap is used for 16-bit 2601 values less than 256. In 32-bit mode, the bitmap is used for 32-bit 2602 values less than 256.) 2603 2604 These two optimizations apply to both pcre_exec() and pcre_dfa_exec(), 2605 and the information is also used by the JIT compiler. The optimiza- 2606 tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option. 2607 You might want to do this if your pattern contains callouts or (*MARK) 2608 and you want to make use of these facilities in cases where matching 2609 fails. 2610 2611 PCRE_NO_START_OPTIMIZE can be specified at either compile time or exe- 2612 cution time. However, if PCRE_NO_START_OPTIMIZE is passed to 2613 pcre_exec(), (that is, after any JIT compilation has happened) JIT exe- 2614 cution is disabled. For JIT execution to work with PCRE_NO_START_OPTI- 2615 MIZE, the option must be set at compile time. 2616 2617 There is a longer discussion of PCRE_NO_START_OPTIMIZE below. 2618 2619 2620LOCALE SUPPORT 2621 2622 PCRE handles caseless matching, and determines whether characters are 2623 letters, digits, or whatever, by reference to a set of tables, indexed 2624 by character code point. When running in UTF-8 mode, or in the 16- or 2625 32-bit libraries, this applies only to characters with code points less 2626 than 256. By default, higher-valued code points never match escapes 2627 such as \w or \d. However, if PCRE is built with Unicode property sup- 2628 port, all characters can be tested with \p and \P, or, alternatively, 2629 the PCRE_UCP option can be set when a pattern is compiled; this causes 2630 \w and friends to use Unicode property support instead of the built-in 2631 tables. 2632 2633 The use of locales with Unicode is discouraged. If you are handling 2634 characters with code points greater than 128, you should either use 2635 Unicode support, or use locales, but not try to mix the two. 2636 2637 PCRE contains an internal set of tables that are used when the final 2638 argument of pcre_compile() is NULL. These are sufficient for many 2639 applications. Normally, the internal tables recognize only ASCII char- 2640 acters. However, when PCRE is built, it is possible to cause the inter- 2641 nal tables to be rebuilt in the default "C" locale of the local system, 2642 which may cause them to be different. 2643 2644 The internal tables can always be overridden by tables supplied by the 2645 application that calls PCRE. These may be created in a different locale 2646 from the default. As more and more applications change to using Uni- 2647 code, the need for this locale support is expected to die away. 2648 2649 External tables are built by calling the pcre_maketables() function, 2650 which has no arguments, in the relevant locale. The result can then be 2651 passed to pcre_compile() as often as necessary. For example, to build 2652 and use tables that are appropriate for the French locale (where 2653 accented characters with values greater than 128 are treated as let- 2654 ters), the following code could be used: 2655 2656 setlocale(LC_CTYPE, "fr_FR"); 2657 tables = pcre_maketables(); 2658 re = pcre_compile(..., tables); 2659 2660 The locale name "fr_FR" is used on Linux and other Unix-like systems; 2661 if you are using Windows, the name for the French locale is "french". 2662 2663 When pcre_maketables() runs, the tables are built in memory that is 2664 obtained via pcre_malloc. It is the caller's responsibility to ensure 2665 that the memory containing the tables remains available for as long as 2666 it is needed. 2667 2668 The pointer that is passed to pcre_compile() is saved with the compiled 2669 pattern, and the same tables are used via this pointer by pcre_study() 2670 and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single pat- 2671 tern, compilation, studying and matching all happen in the same locale, 2672 but different patterns can be processed in different locales. 2673 2674 It is possible to pass a table pointer or NULL (indicating the use of 2675 the internal tables) to pcre_exec() or pcre_dfa_exec() (see the discus- 2676 sion below in the section on matching a pattern). This facility is pro- 2677 vided for use with pre-compiled patterns that have been saved and 2678 reloaded. Character tables are not saved with patterns, so if a non- 2679 standard table was used at compile time, it must be provided again when 2680 the reloaded pattern is matched. Attempting to use this facility to 2681 match a pattern in a different locale from the one in which it was com- 2682 piled is likely to lead to anomalous (usually incorrect) results. 2683 2684 2685INFORMATION ABOUT A PATTERN 2686 2687 int pcre_fullinfo(const pcre *code, const pcre_extra *extra, 2688 int what, void *where); 2689 2690 The pcre_fullinfo() function returns information about a compiled pat- 2691 tern. It replaces the pcre_info() function, which was removed from the 2692 library at version 8.30, after more than 10 years of obsolescence. 2693 2694 The first argument for pcre_fullinfo() is a pointer to the compiled 2695 pattern. The second argument is the result of pcre_study(), or NULL if 2696 the pattern was not studied. The third argument specifies which piece 2697 of information is required, and the fourth argument is a pointer to a 2698 variable to receive the data. The yield of the function is zero for 2699 success, or one of the following negative numbers: 2700 2701 PCRE_ERROR_NULL the argument code was NULL 2702 the argument where was NULL 2703 PCRE_ERROR_BADMAGIC the "magic number" was not found 2704 PCRE_ERROR_BADENDIANNESS the pattern was compiled with different 2705 endianness 2706 PCRE_ERROR_BADOPTION the value of what was invalid 2707 PCRE_ERROR_UNSET the requested field is not set 2708 2709 The "magic number" is placed at the start of each compiled pattern as 2710 an simple check against passing an arbitrary memory pointer. The endi- 2711 anness error can occur if a compiled pattern is saved and reloaded on a 2712 different host. Here is a typical call of pcre_fullinfo(), to obtain 2713 the length of the compiled pattern: 2714 2715 int rc; 2716 size_t length; 2717 rc = pcre_fullinfo( 2718 re, /* result of pcre_compile() */ 2719 sd, /* result of pcre_study(), or NULL */ 2720 PCRE_INFO_SIZE, /* what is required */ 2721 &length); /* where to put the data */ 2722 2723 The possible values for the third argument are defined in pcre.h, and 2724 are as follows: 2725 2726 PCRE_INFO_BACKREFMAX 2727 2728 Return the number of the highest back reference in the pattern. The 2729 fourth argument should point to an int variable. Zero is returned if 2730 there are no back references. 2731 2732 PCRE_INFO_CAPTURECOUNT 2733 2734 Return the number of capturing subpatterns in the pattern. The fourth 2735 argument should point to an int variable. 2736 2737 PCRE_INFO_DEFAULT_TABLES 2738 2739 Return a pointer to the internal default character tables within PCRE. 2740 The fourth argument should point to an unsigned char * variable. This 2741 information call is provided for internal use by the pcre_study() func- 2742 tion. External callers can cause PCRE to use its internal tables by 2743 passing a NULL table pointer. 2744 2745 PCRE_INFO_FIRSTBYTE (deprecated) 2746 2747 Return information about the first data unit of any matched string, for 2748 a non-anchored pattern. The name of this option refers to the 8-bit 2749 library, where data units are bytes. The fourth argument should point 2750 to an int variable. Negative values are used for special cases. How- 2751 ever, this means that when the 32-bit library is in non-UTF-32 mode, 2752 the full 32-bit range of characters cannot be returned. For this rea- 2753 son, this value is deprecated; use PCRE_INFO_FIRSTCHARACTERFLAGS and 2754 PCRE_INFO_FIRSTCHARACTER instead. 2755 2756 If there is a fixed first value, for example, the letter "c" from a 2757 pattern such as (cat|cow|coyote), its value is returned. In the 8-bit 2758 library, the value is always less than 256. In the 16-bit library the 2759 value can be up to 0xffff. In the 32-bit library the value can be up to 2760 0x10ffff. 2761 2762 If there is no fixed first value, and if either 2763 2764 (a) the pattern was compiled with the PCRE_MULTILINE option, and every 2765 branch starts with "^", or 2766 2767 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not 2768 set (if it were set, the pattern would be anchored), 2769 2770 -1 is returned, indicating that the pattern matches only at the start 2771 of a subject string or after any newline within the string. Otherwise 2772 -2 is returned. For anchored patterns, -2 is returned. 2773 2774 PCRE_INFO_FIRSTCHARACTER 2775 2776 Return the value of the first data unit (non-UTF character) of any 2777 matched string in the situation where PCRE_INFO_FIRSTCHARACTERFLAGS 2778 returns 1; otherwise return 0. The fourth argument should point to an 2779 uint_t variable. 2780 2781 In the 8-bit library, the value is always less than 256. In the 16-bit 2782 library the value can be up to 0xffff. In the 32-bit library in UTF-32 2783 mode the value can be up to 0x10ffff, and up to 0xffffffff when not 2784 using UTF-32 mode. 2785 2786 PCRE_INFO_FIRSTCHARACTERFLAGS 2787 2788 Return information about the first data unit of any matched string, for 2789 a non-anchored pattern. The fourth argument should point to an int 2790 variable. 2791 2792 If there is a fixed first value, for example, the letter "c" from a 2793 pattern such as (cat|cow|coyote), 1 is returned, and the character 2794 value can be retrieved using PCRE_INFO_FIRSTCHARACTER. If there is no 2795 fixed first value, and if either 2796 2797 (a) the pattern was compiled with the PCRE_MULTILINE option, and every 2798 branch starts with "^", or 2799 2800 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not 2801 set (if it were set, the pattern would be anchored), 2802 2803 2 is returned, indicating that the pattern matches only at the start of 2804 a subject string or after any newline within the string. Otherwise 0 is 2805 returned. For anchored patterns, 0 is returned. 2806 2807 PCRE_INFO_FIRSTTABLE 2808 2809 If the pattern was studied, and this resulted in the construction of a 2810 256-bit table indicating a fixed set of values for the first data unit 2811 in any matching string, a pointer to the table is returned. Otherwise 2812 NULL is returned. The fourth argument should point to an unsigned char 2813 * variable. 2814 2815 PCRE_INFO_HASCRORLF 2816 2817 Return 1 if the pattern contains any explicit matches for CR or LF 2818 characters, otherwise 0. The fourth argument should point to an int 2819 variable. An explicit match is either a literal CR or LF character, or 2820 \r or \n. 2821 2822 PCRE_INFO_JCHANGED 2823 2824 Return 1 if the (?J) or (?-J) option setting is used in the pattern, 2825 otherwise 0. The fourth argument should point to an int variable. (?J) 2826 and (?-J) set and unset the local PCRE_DUPNAMES option, respectively. 2827 2828 PCRE_INFO_JIT 2829 2830 Return 1 if the pattern was studied with one of the JIT options, and 2831 just-in-time compiling was successful. The fourth argument should point 2832 to an int variable. A return value of 0 means that JIT support is not 2833 available in this version of PCRE, or that the pattern was not studied 2834 with a JIT option, or that the JIT compiler could not handle this par- 2835 ticular pattern. See the pcrejit documentation for details of what can 2836 and cannot be handled. 2837 2838 PCRE_INFO_JITSIZE 2839 2840 If the pattern was successfully studied with a JIT option, return the 2841 size of the JIT compiled code, otherwise return zero. The fourth argu- 2842 ment should point to a size_t variable. 2843 2844 PCRE_INFO_LASTLITERAL 2845 2846 Return the value of the rightmost literal data unit that must exist in 2847 any matched string, other than at its start, if such a value has been 2848 recorded. The fourth argument should point to an int variable. If there 2849 is no such value, -1 is returned. For anchored patterns, a last literal 2850 value is recorded only if it follows something of variable length. For 2851 example, for the pattern /^a\d+z\d+/ the returned value is "z", but for 2852 /^a\dz\d/ the returned value is -1. 2853 2854 Since for the 32-bit library using the non-UTF-32 mode, this function 2855 is unable to return the full 32-bit range of characters, this value is 2856 deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and 2857 PCRE_INFO_REQUIREDCHAR values should be used. 2858 2859 PCRE_INFO_MATCH_EMPTY 2860 2861 Return 1 if the pattern can match an empty string, otherwise 0. The 2862 fourth argument should point to an int variable. 2863 2864 PCRE_INFO_MATCHLIMIT 2865 2866 If the pattern set a match limit by including an item of the form 2867 (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth 2868 argument should point to an unsigned 32-bit integer. If no such value 2869 has been set, the call to pcre_fullinfo() returns the error 2870 PCRE_ERROR_UNSET. 2871 2872 PCRE_INFO_MAXLOOKBEHIND 2873 2874 Return the number of characters (NB not data units) in the longest 2875 lookbehind assertion in the pattern. This information is useful when 2876 doing multi-segment matching using the partial matching facilities. 2877 Note that the simple assertions \b and \B require a one-character look- 2878 behind. \A also registers a one-character lookbehind, though it does 2879 not actually inspect the previous character. This is to ensure that at 2880 least one character from the old segment is retained when a new segment 2881 is processed. Otherwise, if there are no lookbehinds in the pattern, \A 2882 might match incorrectly at the start of a new segment. 2883 2884 PCRE_INFO_MINLENGTH 2885 2886 If the pattern was studied and a minimum length for matching subject 2887 strings was computed, its value is returned. Otherwise the returned 2888 value is -1. The value is a number of characters, which in UTF mode may 2889 be different from the number of data units. The fourth argument should 2890 point to an int variable. A non-negative value is a lower bound to the 2891 length of any matching string. There may not be any strings of that 2892 length that do actually match, but every string that does match is at 2893 least that long. 2894 2895 PCRE_INFO_NAMECOUNT 2896 PCRE_INFO_NAMEENTRYSIZE 2897 PCRE_INFO_NAMETABLE 2898 2899 PCRE supports the use of named as well as numbered capturing parenthe- 2900 ses. The names are just an additional way of identifying the parenthe- 2901 ses, which still acquire numbers. Several convenience functions such as 2902 pcre_get_named_substring() are provided for extracting captured sub- 2903 strings by name. It is also possible to extract the data directly, by 2904 first converting the name to a number in order to access the correct 2905 pointers in the output vector (described with pcre_exec() below). To do 2906 the conversion, you need to use the name-to-number map, which is 2907 described by these three values. 2908 2909 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT 2910 gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size 2911 of each entry; both of these return an int value. The entry size 2912 depends on the length of the longest name. PCRE_INFO_NAMETABLE returns 2913 a pointer to the first entry of the table. This is a pointer to char in 2914 the 8-bit library, where the first two bytes of each entry are the num- 2915 ber of the capturing parenthesis, most significant byte first. In the 2916 16-bit library, the pointer points to 16-bit data units, the first of 2917 which contains the parenthesis number. In the 32-bit library, the 2918 pointer points to 32-bit data units, the first of which contains the 2919 parenthesis number. The rest of the entry is the corresponding name, 2920 zero terminated. 2921 2922 The names are in alphabetical order. If (?| is used to create multiple 2923 groups with the same number, as described in the section on duplicate 2924 subpattern numbers in the pcrepattern page, the groups may be given the 2925 same name, but there is only one entry in the table. Different names 2926 for groups of the same number are not permitted. Duplicate names for 2927 subpatterns with different numbers are permitted, but only if PCRE_DUP- 2928 NAMES is set. They appear in the table in the order in which they were 2929 found in the pattern. In the absence of (?| this is the order of 2930 increasing number; when (?| is used this is not necessarily the case 2931 because later subpatterns may have lower numbers. 2932 2933 As a simple example of the name/number table, consider the following 2934 pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is 2935 set, so white space - including newlines - is ignored): 2936 2937 (?<date> (?<year>(\d\d)?\d\d) - 2938 (?<month>\d\d) - (?<day>\d\d) ) 2939 2940 There are four named subpatterns, so the table has four entries, and 2941 each entry in the table is eight bytes long. The table is as follows, 2942 with non-printing bytes shows in hexadecimal, and undefined bytes shown 2943 as ??: 2944 2945 00 01 d a t e 00 ?? 2946 00 05 d a y 00 ?? ?? 2947 00 04 m o n t h 00 2948 00 02 y e a r 00 ?? 2949 2950 When writing code to extract data from named subpatterns using the 2951 name-to-number map, remember that the length of the entries is likely 2952 to be different for each compiled pattern. 2953 2954 PCRE_INFO_OKPARTIAL 2955 2956 Return 1 if the pattern can be used for partial matching with 2957 pcre_exec(), otherwise 0. The fourth argument should point to an int 2958 variable. From release 8.00, this always returns 1, because the 2959 restrictions that previously applied to partial matching have been 2960 lifted. The pcrepartial documentation gives details of partial match- 2961 ing. 2962 2963 PCRE_INFO_OPTIONS 2964 2965 Return a copy of the options with which the pattern was compiled. The 2966 fourth argument should point to an unsigned long int variable. These 2967 option bits are those specified in the call to pcre_compile(), modified 2968 by any top-level option settings at the start of the pattern itself. In 2969 other words, they are the options that will be in force when matching 2970 starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with 2971 the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE, 2972 and PCRE_EXTENDED. 2973 2974 A pattern is automatically anchored by PCRE if all of its top-level 2975 alternatives begin with one of the following: 2976 2977 ^ unless PCRE_MULTILINE is set 2978 \A always 2979 \G always 2980 .* if PCRE_DOTALL is set and there are no back 2981 references to the subpattern in which .* appears 2982 2983 For such patterns, the PCRE_ANCHORED bit is set in the options returned 2984 by pcre_fullinfo(). 2985 2986 PCRE_INFO_RECURSIONLIMIT 2987 2988 If the pattern set a recursion limit by including an item of the form 2989 (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth 2990 argument should point to an unsigned 32-bit integer. If no such value 2991 has been set, the call to pcre_fullinfo() returns the error 2992 PCRE_ERROR_UNSET. 2993 2994 PCRE_INFO_SIZE 2995 2996 Return the size of the compiled pattern in bytes (for all three 2997 libraries). The fourth argument should point to a size_t variable. This 2998 value does not include the size of the pcre structure that is returned 2999 by pcre_compile(). The value that is passed as the argument to 3000 pcre_malloc() when pcre_compile() is getting memory in which to place 3001 the compiled data is the value returned by this option plus the size of 3002 the pcre structure. Studying a compiled pattern, with or without JIT, 3003 does not alter the value returned by this option. 3004 3005 PCRE_INFO_STUDYSIZE 3006 3007 Return the size in bytes (for all three libraries) of the data block 3008 pointed to by the study_data field in a pcre_extra block. If pcre_extra 3009 is NULL, or there is no study data, zero is returned. The fourth argu- 3010 ment should point to a size_t variable. The study_data field is set by 3011 pcre_study() to record information that will speed up matching (see the 3012 section entitled "Studying a pattern" above). The format of the 3013 study_data block is private, but its length is made available via this 3014 option so that it can be saved and restored (see the pcreprecompile 3015 documentation for details). 3016 3017 PCRE_INFO_REQUIREDCHARFLAGS 3018 3019 Returns 1 if there is a rightmost literal data unit that must exist in 3020 any matched string, other than at its start. The fourth argument should 3021 point to an int variable. If there is no such value, 0 is returned. If 3022 returning 1, the character value itself can be retrieved using 3023 PCRE_INFO_REQUIREDCHAR. 3024 3025 For anchored patterns, a last literal value is recorded only if it fol- 3026 lows something of variable length. For example, for the pattern 3027 /^a\d+z\d+/ the returned value 1 (with "z" returned from 3028 PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0. 3029 3030 PCRE_INFO_REQUIREDCHAR 3031 3032 Return the value of the rightmost literal data unit that must exist in 3033 any matched string, other than at its start, if such a value has been 3034 recorded. The fourth argument should point to an uint32_t variable. If 3035 there is no such value, 0 is returned. 3036 3037 3038REFERENCE COUNTS 3039 3040 int pcre_refcount(pcre *code, int adjust); 3041 3042 The pcre_refcount() function is used to maintain a reference count in 3043 the data block that contains a compiled pattern. It is provided for the 3044 benefit of applications that operate in an object-oriented manner, 3045 where different parts of the application may be using the same compiled 3046 pattern, but you want to free the block when they are all done. 3047 3048 When a pattern is compiled, the reference count field is initialized to 3049 zero. It is changed only by calling this function, whose action is to 3050 add the adjust value (which may be positive or negative) to it. The 3051 yield of the function is the new value. However, the value of the count 3052 is constrained to lie between 0 and 65535, inclusive. If the new value 3053 is outside these limits, it is forced to the appropriate limit value. 3054 3055 Except when it is zero, the reference count is not correctly preserved 3056 if a pattern is compiled on one host and then transferred to a host 3057 whose byte-order is different. (This seems a highly unlikely scenario.) 3058 3059 3060MATCHING A PATTERN: THE TRADITIONAL FUNCTION 3061 3062 int pcre_exec(const pcre *code, const pcre_extra *extra, 3063 const char *subject, int length, int startoffset, 3064 int options, int *ovector, int ovecsize); 3065 3066 The function pcre_exec() is called to match a subject string against a 3067 compiled pattern, which is passed in the code argument. If the pattern 3068 was studied, the result of the study should be passed in the extra 3069 argument. You can call pcre_exec() with the same code and extra argu- 3070 ments as many times as you like, in order to match different subject 3071 strings with the same pattern. 3072 3073 This function is the main matching facility of the library, and it 3074 operates in a Perl-like manner. For specialist use there is also an 3075 alternative matching function, which is described below in the section 3076 about the pcre_dfa_exec() function. 3077 3078 In most applications, the pattern will have been compiled (and option- 3079 ally studied) in the same process that calls pcre_exec(). However, it 3080 is possible to save compiled patterns and study data, and then use them 3081 later in different processes, possibly even on different hosts. For a 3082 discussion about this, see the pcreprecompile documentation. 3083 3084 Here is an example of a simple call to pcre_exec(): 3085 3086 int rc; 3087 int ovector[30]; 3088 rc = pcre_exec( 3089 re, /* result of pcre_compile() */ 3090 NULL, /* we didn't study the pattern */ 3091 "some string", /* the subject string */ 3092 11, /* the length of the subject string */ 3093 0, /* start at offset 0 in the subject */ 3094 0, /* default options */ 3095 ovector, /* vector of integers for substring information */ 3096 30); /* number of elements (NOT size in bytes) */ 3097 3098 Extra data for pcre_exec() 3099 3100 If the extra argument is not NULL, it must point to a pcre_extra data 3101 block. The pcre_study() function returns such a block (when it doesn't 3102 return NULL), but you can also create one for yourself, and pass addi- 3103 tional information in it. The pcre_extra block contains the following 3104 fields (not necessarily in this order): 3105 3106 unsigned long int flags; 3107 void *study_data; 3108 void *executable_jit; 3109 unsigned long int match_limit; 3110 unsigned long int match_limit_recursion; 3111 void *callout_data; 3112 const unsigned char *tables; 3113 unsigned char **mark; 3114 3115 In the 16-bit version of this structure, the mark field has type 3116 "PCRE_UCHAR16 **". 3117 3118 In the 32-bit version of this structure, the mark field has type 3119 "PCRE_UCHAR32 **". 3120 3121 The flags field is used to specify which of the other fields are set. 3122 The flag bits are: 3123 3124 PCRE_EXTRA_CALLOUT_DATA 3125 PCRE_EXTRA_EXECUTABLE_JIT 3126 PCRE_EXTRA_MARK 3127 PCRE_EXTRA_MATCH_LIMIT 3128 PCRE_EXTRA_MATCH_LIMIT_RECURSION 3129 PCRE_EXTRA_STUDY_DATA 3130 PCRE_EXTRA_TABLES 3131 3132 Other flag bits should be set to zero. The study_data field and some- 3133 times the executable_jit field are set in the pcre_extra block that is 3134 returned by pcre_study(), together with the appropriate flag bits. You 3135 should not set these yourself, but you may add to the block by setting 3136 other fields and their corresponding flag bits. 3137 3138 The match_limit field provides a means of preventing PCRE from using up 3139 a vast amount of resources when running patterns that are not going to 3140 match, but which have a very large number of possibilities in their 3141 search trees. The classic example is a pattern that uses nested unlim- 3142 ited repeats. 3143 3144 Internally, pcre_exec() uses a function called match(), which it calls 3145 repeatedly (sometimes recursively). The limit set by match_limit is 3146 imposed on the number of times this function is called during a match, 3147 which has the effect of limiting the amount of backtracking that can 3148 take place. For patterns that are not anchored, the count restarts from 3149 zero for each position in the subject string. 3150 3151 When pcre_exec() is called with a pattern that was successfully studied 3152 with a JIT option, the way that the matching is executed is entirely 3153 different. However, there is still the possibility of runaway matching 3154 that goes on for a very long time, and so the match_limit value is also 3155 used in this case (but in a different way) to limit how long the match- 3156 ing can continue. 3157 3158 The default value for the limit can be set when PCRE is built; the 3159 default default is 10 million, which handles all but the most extreme 3160 cases. You can override the default by suppling pcre_exec() with a 3161 pcre_extra block in which match_limit is set, and 3162 PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is 3163 exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT. 3164 3165 A value for the match limit may also be supplied by an item at the 3166 start of a pattern of the form 3167 3168 (*LIMIT_MATCH=d) 3169 3170 where d is a decimal number. However, such a setting is ignored unless 3171 d is less than the limit set by the caller of pcre_exec() or, if no 3172 such limit is set, less than the default. 3173 3174 The match_limit_recursion field is similar to match_limit, but instead 3175 of limiting the total number of times that match() is called, it limits 3176 the depth of recursion. The recursion depth is a smaller number than 3177 the total number of calls, because not all calls to match() are recur- 3178 sive. This limit is of use only if it is set smaller than match_limit. 3179 3180 Limiting the recursion depth limits the amount of machine stack that 3181 can be used, or, when PCRE has been compiled to use memory on the heap 3182 instead of the stack, the amount of heap memory that can be used. This 3183 limit is not relevant, and is ignored, when matching is done using JIT 3184 compiled code. 3185 3186 The default value for match_limit_recursion can be set when PCRE is 3187 built; the default default is the same value as the default for 3188 match_limit. You can override the default by suppling pcre_exec() with 3189 a pcre_extra block in which match_limit_recursion is set, and 3190 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the 3191 limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT. 3192 3193 A value for the recursion limit may also be supplied by an item at the 3194 start of a pattern of the form 3195 3196 (*LIMIT_RECURSION=d) 3197 3198 where d is a decimal number. However, such a setting is ignored unless 3199 d is less than the limit set by the caller of pcre_exec() or, if no 3200 such limit is set, less than the default. 3201 3202 The callout_data field is used in conjunction with the "callout" fea- 3203 ture, and is described in the pcrecallout documentation. 3204 3205 The tables field is provided for use with patterns that have been pre- 3206 compiled using custom character tables, saved to disc or elsewhere, and 3207 then reloaded, because the tables that were used to compile a pattern 3208 are not saved with it. See the pcreprecompile documentation for a dis- 3209 cussion of saving compiled patterns for later use. If NULL is passed 3210 using this mechanism, it forces PCRE's internal tables to be used. 3211 3212 Warning: The tables that pcre_exec() uses must be the same as those 3213 that were used when the pattern was compiled. If this is not the case, 3214 the behaviour of pcre_exec() is undefined. Therefore, when a pattern is 3215 compiled and matched in the same process, this field should never be 3216 set. In this (the most common) case, the correct table pointer is auto- 3217 matically passed with the compiled pattern from pcre_compile() to 3218 pcre_exec(). 3219 3220 If PCRE_EXTRA_MARK is set in the flags field, the mark field must be 3221 set to point to a suitable variable. If the pattern contains any back- 3222 tracking control verbs such as (*MARK:NAME), and the execution ends up 3223 with a name to pass back, a pointer to the name string (zero termi- 3224 nated) is placed in the variable pointed to by the mark field. The 3225 names are within the compiled pattern; if you wish to retain such a 3226 name you must copy it before freeing the memory of a compiled pattern. 3227 If there is no name to pass back, the variable pointed to by the mark 3228 field is set to NULL. For details of the backtracking control verbs, 3229 see the section entitled "Backtracking control" in the pcrepattern doc- 3230 umentation. 3231 3232 Option bits for pcre_exec() 3233 3234 The unused bits of the options argument for pcre_exec() must be zero. 3235 The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx, 3236 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, 3237 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and 3238 PCRE_PARTIAL_SOFT. 3239 3240 If the pattern was successfully studied with one of the just-in-time 3241 (JIT) compile options, the only supported options for JIT execution are 3242 PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, 3243 PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an 3244 unsupported option is used, JIT execution is disabled and the normal 3245 interpretive code in pcre_exec() is run. 3246 3247 PCRE_ANCHORED 3248 3249 The PCRE_ANCHORED option limits pcre_exec() to matching at the first 3250 matching position. If a pattern was compiled with PCRE_ANCHORED, or 3251 turned out to be anchored by virtue of its contents, it cannot be made 3252 unachored at matching time. 3253 3254 PCRE_BSR_ANYCRLF 3255 PCRE_BSR_UNICODE 3256 3257 These options (which are mutually exclusive) control what the \R escape 3258 sequence matches. The choice is either to match only CR, LF, or CRLF, 3259 or to match any Unicode newline sequence. These options override the 3260 choice that was made or defaulted when the pattern was compiled. 3261 3262 PCRE_NEWLINE_CR 3263 PCRE_NEWLINE_LF 3264 PCRE_NEWLINE_CRLF 3265 PCRE_NEWLINE_ANYCRLF 3266 PCRE_NEWLINE_ANY 3267 3268 These options override the newline definition that was chosen or 3269 defaulted when the pattern was compiled. For details, see the descrip- 3270 tion of pcre_compile() above. During matching, the newline choice 3271 affects the behaviour of the dot, circumflex, and dollar metacharac- 3272 ters. It may also alter the way the match position is advanced after a 3273 match failure for an unanchored pattern. 3274 3275 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is 3276 set, and a match attempt for an unanchored pattern fails when the cur- 3277 rent position is at a CRLF sequence, and the pattern contains no 3278 explicit matches for CR or LF characters, the match position is 3279 advanced by two characters instead of one, in other words, to after the 3280 CRLF. 3281 3282 The above rule is a compromise that makes the most common cases work as 3283 expected. For example, if the pattern is .+A (and the PCRE_DOTALL 3284 option is not set), it does not match the string "\r\nA" because, after 3285 failing at the start, it skips both the CR and the LF before retrying. 3286 However, the pattern [\r\n]A does match that string, because it con- 3287 tains an explicit CR or LF reference, and so advances only by one char- 3288 acter after the first failure. 3289 3290 An explicit match for CR of LF is either a literal appearance of one of 3291 those characters, or one of the \r or \n escape sequences. Implicit 3292 matches such as [^X] do not count, nor does \s (which includes CR and 3293 LF in the characters that it matches). 3294 3295 Notwithstanding the above, anomalous effects may still occur when CRLF 3296 is a valid newline sequence and explicit \r or \n escapes appear in the 3297 pattern. 3298 3299 PCRE_NOTBOL 3300 3301 This option specifies that first character of the subject string is not 3302 the beginning of a line, so the circumflex metacharacter should not 3303 match before it. Setting this without PCRE_MULTILINE (at compile time) 3304 causes circumflex never to match. This option affects only the behav- 3305 iour of the circumflex metacharacter. It does not affect \A. 3306 3307 PCRE_NOTEOL 3308 3309 This option specifies that the end of the subject string is not the end 3310 of a line, so the dollar metacharacter should not match it nor (except 3311 in multiline mode) a newline immediately before it. Setting this with- 3312 out PCRE_MULTILINE (at compile time) causes dollar never to match. This 3313 option affects only the behaviour of the dollar metacharacter. It does 3314 not affect \Z or \z. 3315 3316 PCRE_NOTEMPTY 3317 3318 An empty string is not considered to be a valid match if this option is 3319 set. If there are alternatives in the pattern, they are tried. If all 3320 the alternatives match the empty string, the entire match fails. For 3321 example, if the pattern 3322 3323 a?b? 3324 3325 is applied to a string not beginning with "a" or "b", it matches an 3326 empty string at the start of the subject. With PCRE_NOTEMPTY set, this 3327 match is not valid, so PCRE searches further into the string for occur- 3328 rences of "a" or "b". 3329 3330 PCRE_NOTEMPTY_ATSTART 3331 3332 This is like PCRE_NOTEMPTY, except that an empty string match that is 3333 not at the start of the subject is permitted. If the pattern is 3334 anchored, such a match can occur only if the pattern contains \K. 3335 3336 Perl has no direct equivalent of PCRE_NOTEMPTY or 3337 PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern 3338 match of the empty string within its split() function, and when using 3339 the /g modifier. It is possible to emulate Perl's behaviour after 3340 matching a null string by first trying the match again at the same off- 3341 set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that 3342 fails, by advancing the starting offset (see below) and trying an ordi- 3343 nary match again. There is some code that demonstrates how to do this 3344 in the pcredemo sample program. In the most general case, you have to 3345 check to see if the newline convention recognizes CRLF as a newline, 3346 and if so, and the current character is CR followed by LF, advance the 3347 starting offset by two characters instead of one. 3348 3349 PCRE_NO_START_OPTIMIZE 3350 3351 There are a number of optimizations that pcre_exec() uses at the start 3352 of a match, in order to speed up the process. For example, if it is 3353 known that an unanchored match must start with a specific character, it 3354 searches the subject for that character, and fails immediately if it 3355 cannot find it, without actually running the main matching function. 3356 This means that a special item such as (*COMMIT) at the start of a pat- 3357 tern is not considered until after a suitable starting point for the 3358 match has been found. Also, when callouts or (*MARK) items are in use, 3359 these "start-up" optimizations can cause them to be skipped if the pat- 3360 tern is never actually used. The start-up optimizations are in effect a 3361 pre-scan of the subject that takes place before the pattern is run. 3362 3363 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, 3364 possibly causing performance to suffer, but ensuring that in cases 3365 where the result is "no match", the callouts do occur, and that items 3366 such as (*COMMIT) and (*MARK) are considered at every possible starting 3367 position in the subject string. If PCRE_NO_START_OPTIMIZE is set at 3368 compile time, it cannot be unset at matching time. The use of 3369 PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to 3370 pcre_exec()) disables JIT execution; in this situation, matching is 3371 always done using interpretively. 3372 3373 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching 3374 operation. Consider the pattern 3375 3376 (*COMMIT)ABC 3377 3378 When this is compiled, PCRE records the fact that a match must start 3379 with the character "A". Suppose the subject string is "DEFABC". The 3380 start-up optimization scans along the subject, finds "A" and runs the 3381 first match attempt from there. The (*COMMIT) item means that the pat- 3382 tern must match the current starting position, which in this case, it 3383 does. However, if the same match is run with PCRE_NO_START_OPTIMIZE 3384 set, the initial scan along the subject string does not happen. The 3385 first match attempt is run starting from "D" and when this fails, 3386 (*COMMIT) prevents any further matches being tried, so the overall 3387 result is "no match". If the pattern is studied, more start-up opti- 3388 mizations may be used. For example, a minimum length for the subject 3389 may be recorded. Consider the pattern 3390 3391 (*MARK:A)(X|Y) 3392 3393 The minimum length for a match is one character. If the subject is 3394 "ABC", there will be attempts to match "ABC", "BC", "C", and then 3395 finally an empty string. If the pattern is studied, the final attempt 3396 does not take place, because PCRE knows that the subject is too short, 3397 and so the (*MARK) is never encountered. In this case, studying the 3398 pattern does not affect the overall match result, which is still "no 3399 match", but it does affect the auxiliary information that is returned. 3400 3401 PCRE_NO_UTF8_CHECK 3402 3403 When PCRE_UTF8 is set at compile time, the validity of the subject as a 3404 UTF-8 string is automatically checked when pcre_exec() is subsequently 3405 called. The entire string is checked before any other processing takes 3406 place. The value of startoffset is also checked to ensure that it 3407 points to the start of a UTF-8 character. There is a discussion about 3408 the validity of UTF-8 strings in the pcreunicode page. If an invalid 3409 sequence of bytes is found, pcre_exec() returns the error 3410 PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a 3411 truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In 3412 both cases, information about the precise nature of the error may also 3413 be returned (see the descriptions of these errors in the section enti- 3414 tled Error return values from pcre_exec() below). If startoffset con- 3415 tains a value that does not point to the start of a UTF-8 character (or 3416 to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned. 3417 3418 If you already know that your subject is valid, and you want to skip 3419 these checks for performance reasons, you can set the 3420 PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to 3421 do this for the second and subsequent calls to pcre_exec() if you are 3422 making repeated calls to find all the matches in a single subject 3423 string. However, you should be sure that the value of startoffset 3424 points to the start of a character (or the end of the subject). When 3425 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a 3426 subject or an invalid value of startoffset is undefined. Your program 3427 may crash or loop. 3428 3429 PCRE_PARTIAL_HARD 3430 PCRE_PARTIAL_SOFT 3431 3432 These options turn on the partial matching feature. For backwards com- 3433 patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial 3434 match occurs if the end of the subject string is reached successfully, 3435 but there are not enough subject characters to complete the match. If 3436 this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, 3437 matching continues by testing any remaining alternatives. Only if no 3438 complete match can be found is PCRE_ERROR_PARTIAL returned instead of 3439 PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the 3440 caller is prepared to handle a partial match, but only if no complete 3441 match can be found. 3442 3443 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this 3444 case, if a partial match is found, pcre_exec() immediately returns 3445 PCRE_ERROR_PARTIAL, without considering any other alternatives. In 3446 other words, when PCRE_PARTIAL_HARD is set, a partial match is consid- 3447 ered to be more important that an alternative complete match. 3448 3449 In both cases, the portion of the string that was inspected when the 3450 partial match was found is set as the first matching string. There is a 3451 more detailed discussion of partial and multi-segment matching, with 3452 examples, in the pcrepartial documentation. 3453 3454 The string to be matched by pcre_exec() 3455 3456 The subject string is passed to pcre_exec() as a pointer in subject, a 3457 length in length, and a starting offset in startoffset. The units for 3458 length and startoffset are bytes for the 8-bit library, 16-bit data 3459 items for the 16-bit library, and 32-bit data items for the 32-bit 3460 library. 3461 3462 If startoffset is negative or greater than the length of the subject, 3463 pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is 3464 zero, the search for a match starts at the beginning of the subject, 3465 and this is by far the most common case. In UTF-8 or UTF-16 mode, the 3466 offset must point to the start of a character, or the end of the sub- 3467 ject (in UTF-32 mode, one data unit equals one character, so all off- 3468 sets are valid). Unlike the pattern string, the subject may contain 3469 binary zeroes. 3470 3471 A non-zero starting offset is useful when searching for another match 3472 in the same subject by calling pcre_exec() again after a previous suc- 3473 cess. Setting startoffset differs from just passing over a shortened 3474 string and setting PCRE_NOTBOL in the case of a pattern that begins 3475 with any kind of lookbehind. For example, consider the pattern 3476 3477 \Biss\B 3478 3479 which finds occurrences of "iss" in the middle of words. (\B matches 3480 only if the current position in the subject is not a word boundary.) 3481 When applied to the string "Mississipi" the first call to pcre_exec() 3482 finds the first occurrence. If pcre_exec() is called again with just 3483 the remainder of the subject, namely "issipi", it does not match, 3484 because \B is always false at the start of the subject, which is deemed 3485 to be a word boundary. However, if pcre_exec() is passed the entire 3486 string again, but with startoffset set to 4, it finds the second occur- 3487 rence of "iss" because it is able to look behind the starting point to 3488 discover that it is preceded by a letter. 3489 3490 Finding all the matches in a subject is tricky when the pattern can 3491 match an empty string. It is possible to emulate Perl's /g behaviour by 3492 first trying the match again at the same offset, with the 3493 PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that 3494 fails, advancing the starting offset and trying an ordinary match 3495 again. There is some code that demonstrates how to do this in the pcre- 3496 demo sample program. In the most general case, you have to check to see 3497 if the newline convention recognizes CRLF as a newline, and if so, and 3498 the current character is CR followed by LF, advance the starting offset 3499 by two characters instead of one. 3500 3501 If a non-zero starting offset is passed when the pattern is anchored, 3502 one attempt to match at the given offset is made. This can only succeed 3503 if the pattern does not require the match to be at the start of the 3504 subject. 3505 3506 How pcre_exec() returns captured substrings 3507 3508 In general, a pattern matches a certain portion of the subject, and in 3509 addition, further substrings from the subject may be picked out by 3510 parts of the pattern. Following the usage in Jeffrey Friedl's book, 3511 this is called "capturing" in what follows, and the phrase "capturing 3512 subpattern" is used for a fragment of a pattern that picks out a sub- 3513 string. PCRE supports several other kinds of parenthesized subpattern 3514 that do not cause substrings to be captured. 3515 3516 Captured substrings are returned to the caller via a vector of integers 3517 whose address is passed in ovector. The number of elements in the vec- 3518 tor is passed in ovecsize, which must be a non-negative number. Note: 3519 this argument is NOT the size of ovector in bytes. 3520 3521 The first two-thirds of the vector is used to pass back captured sub- 3522 strings, each substring using a pair of integers. The remaining third 3523 of the vector is used as workspace by pcre_exec() while matching cap- 3524 turing subpatterns, and is not available for passing back information. 3525 The number passed in ovecsize should always be a multiple of three. If 3526 it is not, it is rounded down. 3527 3528 When a match is successful, information about captured substrings is 3529 returned in pairs of integers, starting at the beginning of ovector, 3530 and continuing up to two-thirds of its length at the most. The first 3531 element of each pair is set to the offset of the first character in a 3532 substring, and the second is set to the offset of the first character 3533 after the end of a substring. These values are always data unit off- 3534 sets, even in UTF mode. They are byte offsets in the 8-bit library, 3535 16-bit data item offsets in the 16-bit library, and 32-bit data item 3536 offsets in the 32-bit library. Note: they are not character counts. 3537 3538 The first pair of integers, ovector[0] and ovector[1], identify the 3539 portion of the subject string matched by the entire pattern. The next 3540 pair is used for the first capturing subpattern, and so on. The value 3541 returned by pcre_exec() is one more than the highest numbered pair that 3542 has been set. For example, if two substrings have been captured, the 3543 returned value is 3. If there are no capturing subpatterns, the return 3544 value from a successful match is 1, indicating that just the first pair 3545 of offsets has been set. 3546 3547 If a capturing subpattern is matched repeatedly, it is the last portion 3548 of the string that it matched that is returned. 3549 3550 If the vector is too small to hold all the captured substring offsets, 3551 it is used as far as possible (up to two-thirds of its length), and the 3552 function returns a value of zero. If neither the actual string matched 3553 nor any captured substrings are of interest, pcre_exec() may be called 3554 with ovector passed as NULL and ovecsize as zero. However, if the pat- 3555 tern contains back references and the ovector is not big enough to 3556 remember the related substrings, PCRE has to get additional memory for 3557 use during matching. Thus it is usually advisable to supply an ovector 3558 of reasonable size. 3559 3560 There are some cases where zero is returned (indicating vector over- 3561 flow) when in fact the vector is exactly the right size for the final 3562 match. For example, consider the pattern 3563 3564 (a)(?:(b)c|bd) 3565 3566 If a vector of 6 elements (allowing for only 1 captured substring) is 3567 given with subject string "abd", pcre_exec() will try to set the second 3568 captured string, thereby recording a vector overflow, before failing to 3569 match "c" and backing up to try the second alternative. The zero 3570 return, however, does correctly indicate that the maximum number of 3571 slots (namely 2) have been filled. In similar cases where there is tem- 3572 porary overflow, but the final number of used slots is actually less 3573 than the maximum, a non-zero value is returned. 3574 3575 The pcre_fullinfo() function can be used to find out how many capturing 3576 subpatterns there are in a compiled pattern. The smallest size for 3577 ovector that will allow for n captured substrings, in addition to the 3578 offsets of the substring matched by the whole pattern, is (n+1)*3. 3579 3580 It is possible for capturing subpattern number n+1 to match some part 3581 of the subject when subpattern n has not been used at all. For example, 3582 if the string "abc" is matched against the pattern (a|(z))(bc) the 3583 return from the function is 4, and subpatterns 1 and 3 are matched, but 3584 2 is not. When this happens, both values in the offset pairs corre- 3585 sponding to unused subpatterns are set to -1. 3586 3587 Offset values that correspond to unused subpatterns at the end of the 3588 expression are also set to -1. For example, if the string "abc" is 3589 matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not 3590 matched. The return from the function is 2, because the highest used 3591 capturing subpattern number is 1, and the offsets for for the second 3592 and third capturing subpatterns (assuming the vector is large enough, 3593 of course) are set to -1. 3594 3595 Note: Elements in the first two-thirds of ovector that do not corre- 3596 spond to capturing parentheses in the pattern are never changed. That 3597 is, if a pattern contains n capturing parentheses, no more than ovec- 3598 tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in 3599 the first two-thirds) retain whatever values they previously had. 3600 3601 Some convenience functions are provided for extracting the captured 3602 substrings as separate strings. These are described below. 3603 3604 Error return values from pcre_exec() 3605 3606 If pcre_exec() fails, it returns a negative number. The following are 3607 defined in the header file: 3608 3609 PCRE_ERROR_NOMATCH (-1) 3610 3611 The subject string did not match the pattern. 3612 3613 PCRE_ERROR_NULL (-2) 3614 3615 Either code or subject was passed as NULL, or ovector was NULL and 3616 ovecsize was not zero. 3617 3618 PCRE_ERROR_BADOPTION (-3) 3619 3620 An unrecognized bit was set in the options argument. 3621 3622 PCRE_ERROR_BADMAGIC (-4) 3623 3624 PCRE stores a 4-byte "magic number" at the start of the compiled code, 3625 to catch the case when it is passed a junk pointer and to detect when a 3626 pattern that was compiled in an environment of one endianness is run in 3627 an environment with the other endianness. This is the error that PCRE 3628 gives when the magic number is not present. 3629 3630 PCRE_ERROR_UNKNOWN_OPCODE (-5) 3631 3632 While running the pattern match, an unknown item was encountered in the 3633 compiled pattern. This error could be caused by a bug in PCRE or by 3634 overwriting of the compiled pattern. 3635 3636 PCRE_ERROR_NOMEMORY (-6) 3637 3638 If a pattern contains back references, but the ovector that is passed 3639 to pcre_exec() is not big enough to remember the referenced substrings, 3640 PCRE gets a block of memory at the start of matching to use for this 3641 purpose. If the call via pcre_malloc() fails, this error is given. The 3642 memory is automatically freed at the end of matching. 3643 3644 This error is also given if pcre_stack_malloc() fails in pcre_exec(). 3645 This can happen only when PCRE has been compiled with --disable-stack- 3646 for-recursion. 3647 3648 PCRE_ERROR_NOSUBSTRING (-7) 3649 3650 This error is used by the pcre_copy_substring(), pcre_get_substring(), 3651 and pcre_get_substring_list() functions (see below). It is never 3652 returned by pcre_exec(). 3653 3654 PCRE_ERROR_MATCHLIMIT (-8) 3655 3656 The backtracking limit, as specified by the match_limit field in a 3657 pcre_extra structure (or defaulted) was reached. See the description 3658 above. 3659 3660 PCRE_ERROR_CALLOUT (-9) 3661 3662 This error is never generated by pcre_exec() itself. It is provided for 3663 use by callout functions that want to yield a distinctive error code. 3664 See the pcrecallout documentation for details. 3665 3666 PCRE_ERROR_BADUTF8 (-10) 3667 3668 A string that contains an invalid UTF-8 byte sequence was passed as a 3669 subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of 3670 the output vector (ovecsize) is at least 2, the byte offset to the 3671 start of the the invalid UTF-8 character is placed in the first ele- 3672 ment, and a reason code is placed in the second element. The reason 3673 codes are listed in the following section. For backward compatibility, 3674 if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char- 3675 acter at the end of the subject (reason codes 1 to 5), 3676 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8. 3677 3678 PCRE_ERROR_BADUTF8_OFFSET (-11) 3679 3680 The UTF-8 byte sequence that was passed as a subject was checked and 3681 found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the 3682 value of startoffset did not point to the beginning of a UTF-8 charac- 3683 ter or the end of the subject. 3684 3685 PCRE_ERROR_PARTIAL (-12) 3686 3687 The subject string did not match, but it did match partially. See the 3688 pcrepartial documentation for details of partial matching. 3689 3690 PCRE_ERROR_BADPARTIAL (-13) 3691 3692 This code is no longer in use. It was formerly returned when the 3693 PCRE_PARTIAL option was used with a compiled pattern containing items 3694 that were not supported for partial matching. From release 8.00 3695 onwards, there are no restrictions on partial matching. 3696 3697 PCRE_ERROR_INTERNAL (-14) 3698 3699 An unexpected internal error has occurred. This error could be caused 3700 by a bug in PCRE or by overwriting of the compiled pattern. 3701 3702 PCRE_ERROR_BADCOUNT (-15) 3703 3704 This error is given if the value of the ovecsize argument is negative. 3705 3706 PCRE_ERROR_RECURSIONLIMIT (-21) 3707 3708 The internal recursion limit, as specified by the match_limit_recursion 3709 field in a pcre_extra structure (or defaulted) was reached. See the 3710 description above. 3711 3712 PCRE_ERROR_BADNEWLINE (-23) 3713 3714 An invalid combination of PCRE_NEWLINE_xxx options was given. 3715 3716 PCRE_ERROR_BADOFFSET (-24) 3717 3718 The value of startoffset was negative or greater than the length of the 3719 subject, that is, the value in length. 3720 3721 PCRE_ERROR_SHORTUTF8 (-25) 3722 3723 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject 3724 string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD 3725 option is set. Information about the failure is returned as for 3726 PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but 3727 this special error code for PCRE_PARTIAL_HARD precedes the implementa- 3728 tion of returned information; it is retained for backwards compatibil- 3729 ity. 3730 3731 PCRE_ERROR_RECURSELOOP (-26) 3732 3733 This error is returned when pcre_exec() detects a recursion loop within 3734 the pattern. Specifically, it means that either the whole pattern or a 3735 subpattern has been called recursively for the second time at the same 3736 position in the subject string. Some simple patterns that might do this 3737 are detected and faulted at compile time, but more complicated cases, 3738 in particular mutual recursions between two different subpatterns, can- 3739 not be detected until run time. 3740 3741 PCRE_ERROR_JIT_STACKLIMIT (-27) 3742 3743 This error is returned when a pattern that was successfully studied 3744 using a JIT compile option is being matched, but the memory available 3745 for the just-in-time processing stack is not large enough. See the 3746 pcrejit documentation for more details. 3747 3748 PCRE_ERROR_BADMODE (-28) 3749 3750 This error is given if a pattern that was compiled by the 8-bit library 3751 is passed to a 16-bit or 32-bit library function, or vice versa. 3752 3753 PCRE_ERROR_BADENDIANNESS (-29) 3754 3755 This error is given if a pattern that was compiled and saved is 3756 reloaded on a host with different endianness. The utility function 3757 pcre_pattern_to_host_byte_order() can be used to convert such a pattern 3758 so that it runs on the new host. 3759 3760 PCRE_ERROR_JIT_BADOPTION 3761 3762 This error is returned when a pattern that was successfully studied 3763 using a JIT compile option is being matched, but the matching mode 3764 (partial or complete match) does not correspond to any JIT compilation 3765 mode. When the JIT fast path function is used, this error may be also 3766 given for invalid options. See the pcrejit documentation for more 3767 details. 3768 3769 PCRE_ERROR_BADLENGTH (-32) 3770 3771 This error is given if pcre_exec() is called with a negative value for 3772 the length argument. 3773 3774 Error numbers -16 to -20, -22, and 30 are not used by pcre_exec(). 3775 3776 Reason codes for invalid UTF-8 strings 3777 3778 This section applies only to the 8-bit library. The corresponding 3779 information for the 16-bit and 32-bit libraries is given in the pcre16 3780 and pcre32 pages. 3781 3782 When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT- 3783 UTF8, and the size of the output vector (ovecsize) is at least 2, the 3784 offset of the start of the invalid UTF-8 character is placed in the 3785 first output vector element (ovector[0]) and a reason code is placed in 3786 the second element (ovector[1]). The reason codes are given names in 3787 the pcre.h header file: 3788 3789 PCRE_UTF8_ERR1 3790 PCRE_UTF8_ERR2 3791 PCRE_UTF8_ERR3 3792 PCRE_UTF8_ERR4 3793 PCRE_UTF8_ERR5 3794 3795 The string ends with a truncated UTF-8 character; the code specifies 3796 how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 3797 characters to be no longer than 4 bytes, the encoding scheme (origi- 3798 nally defined by RFC 2279) allows for up to 6 bytes, and this is 3799 checked first; hence the possibility of 4 or 5 missing bytes. 3800 3801 PCRE_UTF8_ERR6 3802 PCRE_UTF8_ERR7 3803 PCRE_UTF8_ERR8 3804 PCRE_UTF8_ERR9 3805 PCRE_UTF8_ERR10 3806 3807 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of 3808 the character do not have the binary value 0b10 (that is, either the 3809 most significant bit is 0, or the next bit is 1). 3810 3811 PCRE_UTF8_ERR11 3812 PCRE_UTF8_ERR12 3813 3814 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes 3815 long; these code points are excluded by RFC 3629. 3816 3817 PCRE_UTF8_ERR13 3818 3819 A 4-byte character has a value greater than 0x10fff; these code points 3820 are excluded by RFC 3629. 3821 3822 PCRE_UTF8_ERR14 3823 3824 A 3-byte character has a value in the range 0xd800 to 0xdfff; this 3825 range of code points are reserved by RFC 3629 for use with UTF-16, and 3826 so are excluded from UTF-8. 3827 3828 PCRE_UTF8_ERR15 3829 PCRE_UTF8_ERR16 3830 PCRE_UTF8_ERR17 3831 PCRE_UTF8_ERR18 3832 PCRE_UTF8_ERR19 3833 3834 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes 3835 for a value that can be represented by fewer bytes, which is invalid. 3836 For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- 3837 rect coding uses just one byte. 3838 3839 PCRE_UTF8_ERR20 3840 3841 The two most significant bits of the first byte of a character have the 3842 binary value 0b10 (that is, the most significant bit is 1 and the sec- 3843 ond is 0). Such a byte can only validly occur as the second or subse- 3844 quent byte of a multi-byte character. 3845 3846 PCRE_UTF8_ERR21 3847 3848 The first byte of a character has the value 0xfe or 0xff. These values 3849 can never occur in a valid UTF-8 string. 3850 3851 PCRE_UTF8_ERR22 3852 3853 This error code was formerly used when the presence of a so-called 3854 "non-character" caused an error. Unicode corrigendum #9 makes it clear 3855 that such characters should not cause a string to be rejected, and so 3856 this code is no longer in use and is never returned. 3857 3858 3859EXTRACTING CAPTURED SUBSTRINGS BY NUMBER 3860 3861 int pcre_copy_substring(const char *subject, int *ovector, 3862 int stringcount, int stringnumber, char *buffer, 3863 int buffersize); 3864 3865 int pcre_get_substring(const char *subject, int *ovector, 3866 int stringcount, int stringnumber, 3867 const char **stringptr); 3868 3869 int pcre_get_substring_list(const char *subject, 3870 int *ovector, int stringcount, const char ***listptr); 3871 3872 Captured substrings can be accessed directly by using the offsets 3873 returned by pcre_exec() in ovector. For convenience, the functions 3874 pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub- 3875 string_list() are provided for extracting captured substrings as new, 3876 separate, zero-terminated strings. These functions identify substrings 3877 by number. The next section describes functions for extracting named 3878 substrings. 3879 3880 A substring that contains a binary zero is correctly extracted and has 3881 a further zero added on the end, but the result is not, of course, a C 3882 string. However, you can process such a string by referring to the 3883 length that is returned by pcre_copy_substring() and pcre_get_sub- 3884 string(). Unfortunately, the interface to pcre_get_substring_list() is 3885 not adequate for handling strings containing binary zeros, because the 3886 end of the final string is not independently indicated. 3887 3888 The first three arguments are the same for all three of these func- 3889 tions: subject is the subject string that has just been successfully 3890 matched, ovector is a pointer to the vector of integer offsets that was 3891 passed to pcre_exec(), and stringcount is the number of substrings that 3892 were captured by the match, including the substring that matched the 3893 entire regular expression. This is the value returned by pcre_exec() if 3894 it is greater than zero. If pcre_exec() returned zero, indicating that 3895 it ran out of space in ovector, the value passed as stringcount should 3896 be the number of elements in the vector divided by three. 3897 3898 The functions pcre_copy_substring() and pcre_get_substring() extract a 3899 single substring, whose number is given as stringnumber. A value of 3900 zero extracts the substring that matched the entire pattern, whereas 3901 higher values extract the captured substrings. For pcre_copy_sub- 3902 string(), the string is placed in buffer, whose length is given by 3903 buffersize, while for pcre_get_substring() a new block of memory is 3904 obtained via pcre_malloc, and its address is returned via stringptr. 3905 The yield of the function is the length of the string, not including 3906 the terminating zero, or one of these error codes: 3907 3908 PCRE_ERROR_NOMEMORY (-6) 3909 3910 The buffer was too small for pcre_copy_substring(), or the attempt to 3911 get memory failed for pcre_get_substring(). 3912 3913 PCRE_ERROR_NOSUBSTRING (-7) 3914 3915 There is no substring whose number is stringnumber. 3916 3917 The pcre_get_substring_list() function extracts all available sub- 3918 strings and builds a list of pointers to them. All this is done in a 3919 single block of memory that is obtained via pcre_malloc. The address of 3920 the memory block is returned via listptr, which is also the start of 3921 the list of string pointers. The end of the list is marked by a NULL 3922 pointer. The yield of the function is zero if all went well, or the 3923 error code 3924 3925 PCRE_ERROR_NOMEMORY (-6) 3926 3927 if the attempt to get the memory block failed. 3928 3929 When any of these functions encounter a substring that is unset, which 3930 can happen when capturing subpattern number n+1 matches some part of 3931 the subject, but subpattern n has not been used at all, they return an 3932 empty string. This can be distinguished from a genuine zero-length sub- 3933 string by inspecting the appropriate offset in ovector, which is nega- 3934 tive for unset substrings. 3935 3936 The two convenience functions pcre_free_substring() and pcre_free_sub- 3937 string_list() can be used to free the memory returned by a previous 3938 call of pcre_get_substring() or pcre_get_substring_list(), respec- 3939 tively. They do nothing more than call the function pointed to by 3940 pcre_free, which of course could be called directly from a C program. 3941 However, PCRE is used in some situations where it is linked via a spe- 3942 cial interface to another programming language that cannot use 3943 pcre_free directly; it is for these cases that the functions are pro- 3944 vided. 3945 3946 3947EXTRACTING CAPTURED SUBSTRINGS BY NAME 3948 3949 int pcre_get_stringnumber(const pcre *code, 3950 const char *name); 3951 3952 int pcre_copy_named_substring(const pcre *code, 3953 const char *subject, int *ovector, 3954 int stringcount, const char *stringname, 3955 char *buffer, int buffersize); 3956 3957 int pcre_get_named_substring(const pcre *code, 3958 const char *subject, int *ovector, 3959 int stringcount, const char *stringname, 3960 const char **stringptr); 3961 3962 To extract a substring by name, you first have to find associated num- 3963 ber. For example, for this pattern 3964 3965 (a+)b(?<xxx>\d+)... 3966 3967 the number of the subpattern called "xxx" is 2. If the name is known to 3968 be unique (PCRE_DUPNAMES was not set), you can find the number from the 3969 name by calling pcre_get_stringnumber(). The first argument is the com- 3970 piled pattern, and the second is the name. The yield of the function is 3971 the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no 3972 subpattern of that name. 3973 3974 Given the number, you can extract the substring directly, or use one of 3975 the functions described in the previous section. For convenience, there 3976 are also two functions that do the whole job. 3977 3978 Most of the arguments of pcre_copy_named_substring() and 3979 pcre_get_named_substring() are the same as those for the similarly 3980 named functions that extract by number. As these are described in the 3981 previous section, they are not re-described here. There are just two 3982 differences: 3983 3984 First, instead of a substring number, a substring name is given. Sec- 3985 ond, there is an extra argument, given at the start, which is a pointer 3986 to the compiled pattern. This is needed in order to gain access to the 3987 name-to-number translation table. 3988 3989 These functions call pcre_get_stringnumber(), and if it succeeds, they 3990 then call pcre_copy_substring() or pcre_get_substring(), as appropri- 3991 ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the 3992 behaviour may not be what you want (see the next section). 3993 3994 Warning: If the pattern uses the (?| feature to set up multiple subpat- 3995 terns with the same number, as described in the section on duplicate 3996 subpattern numbers in the pcrepattern page, you cannot use names to 3997 distinguish the different subpatterns, because names are not included 3998 in the compiled code. The matching process uses only numbers. For this 3999 reason, the use of different names for subpatterns of the same number 4000 causes an error at compile time. 4001 4002 4003DUPLICATE SUBPATTERN NAMES 4004 4005 int pcre_get_stringtable_entries(const pcre *code, 4006 const char *name, char **first, char **last); 4007 4008 When a pattern is compiled with the PCRE_DUPNAMES option, names for 4009 subpatterns are not required to be unique. (Duplicate names are always 4010 allowed for subpatterns with the same number, created by using the (?| 4011 feature. Indeed, if such subpatterns are named, they are required to 4012 use the same names.) 4013 4014 Normally, patterns with duplicate names are such that in any one match, 4015 only one of the named subpatterns participates. An example is shown in 4016 the pcrepattern documentation. 4017 4018 When duplicates are present, pcre_copy_named_substring() and 4019 pcre_get_named_substring() return the first substring corresponding to 4020 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING 4021 (-7) is returned; no data is returned. The pcre_get_stringnumber() 4022 function returns one of the numbers that are associated with the name, 4023 but it is not defined which it is. 4024 4025 If you want to get full details of all captured substrings for a given 4026 name, you must use the pcre_get_stringtable_entries() function. The 4027 first argument is the compiled pattern, and the second is the name. The 4028 third and fourth are pointers to variables which are updated by the 4029 function. After it has run, they point to the first and last entries in 4030 the name-to-number table for the given name. The function itself 4031 returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if 4032 there are none. The format of the table is described above in the sec- 4033 tion entitled Information about a pattern above. Given all the rele- 4034 vant entries for the name, you can extract each of their numbers, and 4035 hence the captured data, if any. 4036 4037 4038FINDING ALL POSSIBLE MATCHES 4039 4040 The traditional matching function uses a similar algorithm to Perl, 4041 which stops when it finds the first match, starting at a given point in 4042 the subject. If you want to find all possible matches, or the longest 4043 possible match, consider using the alternative matching function (see 4044 below) instead. If you cannot use the alternative function, but still 4045 need to find all possible matches, you can kludge it up by making use 4046 of the callout facility, which is described in the pcrecallout documen- 4047 tation. 4048 4049 What you have to do is to insert a callout right at the end of the pat- 4050 tern. When your callout function is called, extract and save the cur- 4051 rent matched substring. Then return 1, which forces pcre_exec() to 4052 backtrack and try other alternatives. Ultimately, when it runs out of 4053 matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. 4054 4055 4056OBTAINING AN ESTIMATE OF STACK USAGE 4057 4058 Matching certain patterns using pcre_exec() can use a lot of process 4059 stack, which in certain environments can be rather limited in size. 4060 Some users find it helpful to have an estimate of the amount of stack 4061 that is used by pcre_exec(), to help them set recursion limits, as 4062 described in the pcrestack documentation. The estimate that is output 4063 by pcretest when called with the -m and -C options is obtained by call- 4064 ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its 4065 first five arguments. 4066 4067 Normally, if its first argument is NULL, pcre_exec() immediately 4068 returns the negative error code PCRE_ERROR_NULL, but with this special 4069 combination of arguments, it returns instead a negative number whose 4070 absolute value is the approximate stack frame size in bytes. (A nega- 4071 tive number is used so that it is clear that no match has happened.) 4072 The value is approximate because in some cases, recursive calls to 4073 pcre_exec() occur when there are one or two additional variables on the 4074 stack. 4075 4076 If PCRE has been compiled to use the heap instead of the stack for 4077 recursion, the value returned is the size of each block that is 4078 obtained from the heap. 4079 4080 4081MATCHING A PATTERN: THE ALTERNATIVE FUNCTION 4082 4083 int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, 4084 const char *subject, int length, int startoffset, 4085 int options, int *ovector, int ovecsize, 4086 int *workspace, int wscount); 4087 4088 The function pcre_dfa_exec() is called to match a subject string 4089 against a compiled pattern, using a matching algorithm that scans the 4090 subject string just once, and does not backtrack. This has different 4091 characteristics to the normal algorithm, and is not compatible with 4092 Perl. Some of the features of PCRE patterns are not supported. Never- 4093 theless, there are times when this kind of matching can be useful. For 4094 a discussion of the two matching algorithms, and a list of features 4095 that pcre_dfa_exec() does not support, see the pcrematching documenta- 4096 tion. 4097 4098 The arguments for the pcre_dfa_exec() function are the same as for 4099 pcre_exec(), plus two extras. The ovector argument is used in a differ- 4100 ent way, and this is described below. The other common arguments are 4101 used in the same way as for pcre_exec(), so their description is not 4102 repeated here. 4103 4104 The two additional arguments provide workspace for the function. The 4105 workspace vector should contain at least 20 elements. It is used for 4106 keeping track of multiple paths through the pattern tree. More 4107 workspace will be needed for patterns and subjects where there are a 4108 lot of potential matches. 4109 4110 Here is an example of a simple call to pcre_dfa_exec(): 4111 4112 int rc; 4113 int ovector[10]; 4114 int wspace[20]; 4115 rc = pcre_dfa_exec( 4116 re, /* result of pcre_compile() */ 4117 NULL, /* we didn't study the pattern */ 4118 "some string", /* the subject string */ 4119 11, /* the length of the subject string */ 4120 0, /* start at offset 0 in the subject */ 4121 0, /* default options */ 4122 ovector, /* vector of integers for substring information */ 4123 10, /* number of elements (NOT size in bytes) */ 4124 wspace, /* working space vector */ 4125 20); /* number of elements (NOT size in bytes) */ 4126 4127 Option bits for pcre_dfa_exec() 4128 4129 The unused bits of the options argument for pcre_dfa_exec() must be 4130 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW- 4131 LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, 4132 PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, 4133 PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR- 4134 TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last 4135 four of these are exactly the same as for pcre_exec(), so their 4136 description is not repeated here. 4137 4138 PCRE_PARTIAL_HARD 4139 PCRE_PARTIAL_SOFT 4140 4141 These have the same general effect as they do for pcre_exec(), but the 4142 details are slightly different. When PCRE_PARTIAL_HARD is set for 4143 pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub- 4144 ject is reached and there is still at least one matching possibility 4145 that requires additional characters. This happens even if some complete 4146 matches have also been found. When PCRE_PARTIAL_SOFT is set, the return 4147 code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end 4148 of the subject is reached, there have been no complete matches, but 4149 there is still at least one matching possibility. The portion of the 4150 string that was inspected when the longest partial match was found is 4151 set as the first matching string in both cases. There is a more 4152 detailed discussion of partial and multi-segment matching, with exam- 4153 ples, in the pcrepartial documentation. 4154 4155 PCRE_DFA_SHORTEST 4156 4157 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to 4158 stop as soon as it has found one match. Because of the way the alterna- 4159 tive algorithm works, this is necessarily the shortest possible match 4160 at the first possible matching point in the subject string. 4161 4162 PCRE_DFA_RESTART 4163 4164 When pcre_dfa_exec() returns a partial match, it is possible to call it 4165 again, with additional subject characters, and have it continue with 4166 the same match. The PCRE_DFA_RESTART option requests this action; when 4167 it is set, the workspace and wscount options must reference the same 4168 vector as before because data about the match so far is left in them 4169 after a partial match. There is more discussion of this facility in the 4170 pcrepartial documentation. 4171 4172 Successful returns from pcre_dfa_exec() 4173 4174 When pcre_dfa_exec() succeeds, it may have matched more than one sub- 4175 string in the subject. Note, however, that all the matches from one run 4176 of the function start at the same point in the subject. The shorter 4177 matches are all initial substrings of the longer matches. For example, 4178 if the pattern 4179 4180 <.*> 4181 4182 is matched against the string 4183 4184 This is <something> <something else> <something further> no more 4185 4186 the three matched strings are 4187 4188 <something> 4189 <something> <something else> 4190 <something> <something else> <something further> 4191 4192 On success, the yield of the function is a number greater than zero, 4193 which is the number of matched substrings. The substrings themselves 4194 are returned in ovector. Each string uses two elements; the first is 4195 the offset to the start, and the second is the offset to the end. In 4196 fact, all the strings have the same start offset. (Space could have 4197 been saved by giving this only once, but it was decided to retain some 4198 compatibility with the way pcre_exec() returns data, even though the 4199 meaning of the strings is different.) 4200 4201 The strings are returned in reverse order of length; that is, the long- 4202 est matching string is given first. If there were too many matches to 4203 fit into ovector, the yield of the function is zero, and the vector is 4204 filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() 4205 can use the entire ovector for returning matched strings. 4206 4207 NOTE: PCRE's "auto-possessification" optimization usually applies to 4208 character repeats at the end of a pattern (as well as internally). For 4209 example, the pattern "a\d+" is compiled as if it were "a\d++" because 4210 there is no point even considering the possibility of backtracking into 4211 the repeated digits. For DFA matching, this means that only one possi- 4212 ble match is found. If you really do want multiple matches in such 4213 cases, either use an ungreedy repeat ("a\d+?") or set the 4214 PCRE_NO_AUTO_POSSESS option when compiling. 4215 4216 Error returns from pcre_dfa_exec() 4217 4218 The pcre_dfa_exec() function returns a negative number when it fails. 4219 Many of the errors are the same as for pcre_exec(), and these are 4220 described above. There are in addition the following errors that are 4221 specific to pcre_dfa_exec(): 4222 4223 PCRE_ERROR_DFA_UITEM (-16) 4224 4225 This return is given if pcre_dfa_exec() encounters an item in the pat- 4226 tern that it does not support, for instance, the use of \C or a back 4227 reference. 4228 4229 PCRE_ERROR_DFA_UCOND (-17) 4230 4231 This return is given if pcre_dfa_exec() encounters a condition item 4232 that uses a back reference for the condition, or a test for recursion 4233 in a specific group. These are not supported. 4234 4235 PCRE_ERROR_DFA_UMLIMIT (-18) 4236 4237 This return is given if pcre_dfa_exec() is called with an extra block 4238 that contains a setting of the match_limit or match_limit_recursion 4239 fields. This is not supported (these fields are meaningless for DFA 4240 matching). 4241 4242 PCRE_ERROR_DFA_WSSIZE (-19) 4243 4244 This return is given if pcre_dfa_exec() runs out of space in the 4245 workspace vector. 4246 4247 PCRE_ERROR_DFA_RECURSE (-20) 4248 4249 When a recursive subpattern is processed, the matching function calls 4250 itself recursively, using private vectors for ovector and workspace. 4251 This error is given if the output vector is not large enough. This 4252 should be extremely rare, as a vector of size 1000 is used. 4253 4254 PCRE_ERROR_DFA_BADRESTART (-30) 4255 4256 When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some 4257 plausibility checks are made on the contents of the workspace, which 4258 should contain data about the previous partial match. If any of these 4259 checks fail, this error is given. 4260 4261 4262SEE ALSO 4263 4264 pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), 4265 pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre- 4266 sample(3), pcrestack(3). 4267 4268 4269AUTHOR 4270 4271 Philip Hazel 4272 University Computing Service 4273 Cambridge CB2 3QH, England. 4274 4275 4276REVISION 4277 4278 Last updated: 18 December 2015 4279 Copyright (c) 1997-2015 University of Cambridge. 4280------------------------------------------------------------------------------ 4281 4282 4283PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3) 4284 4285 4286 4287NAME 4288 PCRE - Perl-compatible regular expressions 4289 4290SYNOPSIS 4291 4292 #include <pcre.h> 4293 4294 int (*pcre_callout)(pcre_callout_block *); 4295 4296 int (*pcre16_callout)(pcre16_callout_block *); 4297 4298 int (*pcre32_callout)(pcre32_callout_block *); 4299 4300 4301DESCRIPTION 4302 4303 PCRE provides a feature called "callout", which is a means of temporar- 4304 ily passing control to the caller of PCRE in the middle of pattern 4305 matching. The caller of PCRE provides an external function by putting 4306 its entry point in the global variable pcre_callout (pcre16_callout for 4307 the 16-bit library, pcre32_callout for the 32-bit library). By default, 4308 this variable contains NULL, which disables all calling out. 4309 4310 Within a regular expression, (?C) indicates the points at which the 4311 external function is to be called. Different callout points can be 4312 identified by putting a number less than 256 after the letter C. The 4313 default value is zero. For example, this pattern has two callout 4314 points: 4315 4316 (?C1)abc(?C2)def 4317 4318 If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, 4319 PCRE automatically inserts callouts, all with number 255, before each 4320 item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the 4321 pattern 4322 4323 A(\d{2}|--) 4324 4325 it is processed as if it were 4326 4327 (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) 4328 4329 Notice that there is a callout before and after each parenthesis and 4330 alternation bar. If the pattern contains a conditional group whose con- 4331 dition is an assertion, an automatic callout is inserted immediately 4332 before the condition. Such a callout may also be inserted explicitly, 4333 for example: 4334 4335 (?(?C9)(?=a)ab|de) 4336 4337 This applies only to assertion conditions (because they are themselves 4338 independent groups). 4339 4340 Automatic callouts can be used for tracking the progress of pattern 4341 matching. The pcretest program has a pattern qualifier (/C) that sets 4342 automatic callouts; when it is used, the output indicates how the pat- 4343 tern is being matched. This is useful information when you are trying 4344 to optimize the performance of a particular pattern. 4345 4346 4347MISSING CALLOUTS 4348 4349 You should be aware that, because of optimizations in the way PCRE com- 4350 piles and matches patterns, callouts sometimes do not happen exactly as 4351 you might expect. 4352 4353 At compile time, PCRE "auto-possessifies" repeated items when it knows 4354 that what follows cannot be part of the repeat. For example, a+[bc] is 4355 compiled as if it were a++[bc]. The pcretest output when this pattern 4356 is anchored and then applied with automatic callouts to the string 4357 "aaaa" is: 4358 4359 --->aaaa 4360 +0 ^ ^ 4361 +1 ^ a+ 4362 +3 ^ ^ [bc] 4363 No match 4364 4365 This indicates that when matching [bc] fails, there is no backtracking 4366 into a+ and therefore the callouts that would be taken for the back- 4367 tracks do not occur. You can disable the auto-possessify feature by 4368 passing PCRE_NO_AUTO_POSSESS to pcre_compile(), or starting the pattern 4369 with (*NO_AUTO_POSSESS). If this is done in pcretest (using the /O 4370 qualifier), the output changes to this: 4371 4372 --->aaaa 4373 +0 ^ ^ 4374 +1 ^ a+ 4375 +3 ^ ^ [bc] 4376 +3 ^ ^ [bc] 4377 +3 ^ ^ [bc] 4378 +3 ^^ [bc] 4379 No match 4380 4381 This time, when matching [bc] fails, the matcher backtracks into a+ and 4382 tries again, repeatedly, until a+ itself fails. 4383 4384 Other optimizations that provide fast "no match" results also affect 4385 callouts. For example, if the pattern is 4386 4387 ab(?C4)cd 4388 4389 PCRE knows that any matching string must contain the letter "d". If the 4390 subject string is "abyz", the lack of "d" means that matching doesn't 4391 ever start, and the callout is never reached. However, with "abyd", 4392 though the result is still no match, the callout is obeyed. 4393 4394 If the pattern is studied, PCRE knows the minimum length of a matching 4395 string, and will immediately give a "no match" return without actually 4396 running a match if the subject is not long enough, or, for unanchored 4397 patterns, if it has been scanned far enough. 4398 4399 You can disable these optimizations by passing the PCRE_NO_START_OPTI- 4400 MIZE option to the matching function, or by starting the pattern with 4401 (*NO_START_OPT). This slows down the matching process, but does ensure 4402 that callouts such as the example above are obeyed. 4403 4404 4405THE CALLOUT INTERFACE 4406 4407 During matching, when PCRE reaches a callout point, the external func- 4408 tion defined by pcre_callout or pcre[16|32]_callout is called (if it is 4409 set). This applies to both normal and DFA matching. The only argument 4410 to the callout function is a pointer to a pcre_callout or 4411 pcre[16|32]_callout block. These structures contains the following 4412 fields: 4413 4414 int version; 4415 int callout_number; 4416 int *offset_vector; 4417 const char *subject; (8-bit version) 4418 PCRE_SPTR16 subject; (16-bit version) 4419 PCRE_SPTR32 subject; (32-bit version) 4420 int subject_length; 4421 int start_match; 4422 int current_position; 4423 int capture_top; 4424 int capture_last; 4425 void *callout_data; 4426 int pattern_position; 4427 int next_item_length; 4428 const unsigned char *mark; (8-bit version) 4429 const PCRE_UCHAR16 *mark; (16-bit version) 4430 const PCRE_UCHAR32 *mark; (32-bit version) 4431 4432 The version field is an integer containing the version number of the 4433 block format. The initial version was 0; the current version is 2. The 4434 version number will change again in future if additional fields are 4435 added, but the intention is never to remove any of the existing fields. 4436 4437 The callout_number field contains the number of the callout, as com- 4438 piled into the pattern (that is, the number after ?C for manual call- 4439 outs, and 255 for automatically generated callouts). 4440 4441 The offset_vector field is a pointer to the vector of offsets that was 4442 passed by the caller to the matching function. When pcre_exec() or 4443 pcre[16|32]_exec() is used, the contents can be inspected, in order to 4444 extract substrings that have been matched so far, in the same way as 4445 for extracting substrings after a match has completed. For the DFA 4446 matching functions, this field is not useful. 4447 4448 The subject and subject_length fields contain copies of the values that 4449 were passed to the matching function. 4450 4451 The start_match field normally contains the offset within the subject 4452 at which the current match attempt started. However, if the escape 4453 sequence \K has been encountered, this value is changed to reflect the 4454 modified starting point. If the pattern is not anchored, the callout 4455 function may be called several times from the same point in the pattern 4456 for different starting points in the subject. 4457 4458 The current_position field contains the offset within the subject of 4459 the current match pointer. 4460 4461 When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top 4462 field contains one more than the number of the highest numbered cap- 4463 tured substring so far. If no substrings have been captured, the value 4464 of capture_top is one. This is always the case when the DFA functions 4465 are used, because they do not support captured substrings. 4466 4467 The capture_last field contains the number of the most recently cap- 4468 tured substring. However, when a recursion exits, the value reverts to 4469 what it was outside the recursion, as do the values of all captured 4470 substrings. If no substrings have been captured, the value of cap- 4471 ture_last is -1. This is always the case for the DFA matching func- 4472 tions. 4473 4474 The callout_data field contains a value that is passed to a matching 4475 function specifically so that it can be passed back in callouts. It is 4476 passed in the callout_data field of a pcre_extra or pcre[16|32]_extra 4477 data structure. If no such data was passed, the value of callout_data 4478 in a callout block is NULL. There is a description of the pcre_extra 4479 structure in the pcreapi documentation. 4480 4481 The pattern_position field is present from version 1 of the callout 4482 structure. It contains the offset to the next item to be matched in the 4483 pattern string. 4484 4485 The next_item_length field is present from version 1 of the callout 4486 structure. It contains the length of the next item to be matched in the 4487 pattern string. When the callout immediately precedes an alternation 4488 bar, a closing parenthesis, or the end of the pattern, the length is 4489 zero. When the callout precedes an opening parenthesis, the length is 4490 that of the entire subpattern. 4491 4492 The pattern_position and next_item_length fields are intended to help 4493 in distinguishing between different automatic callouts, which all have 4494 the same callout number. However, they are set for all callouts. 4495 4496 The mark field is present from version 2 of the callout structure. In 4497 callouts from pcre_exec() or pcre[16|32]_exec() it contains a pointer 4498 to the zero-terminated name of the most recently passed (*MARK), 4499 (*PRUNE), or (*THEN) item in the match, or NULL if no such items have 4500 been passed. Instances of (*PRUNE) or (*THEN) without a name do not 4501 obliterate a previous (*MARK). In callouts from the DFA matching func- 4502 tions this field always contains NULL. 4503 4504 4505RETURN VALUES 4506 4507 The external callout function returns an integer to PCRE. If the value 4508 is zero, matching proceeds as normal. If the value is greater than 4509 zero, matching fails at the current point, but the testing of other 4510 matching possibilities goes ahead, just as if a lookahead assertion had 4511 failed. If the value is less than zero, the match is abandoned, the 4512 matching function returns the negative value. 4513 4514 Negative values should normally be chosen from the set of 4515 PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan- 4516 dard "no match" failure. The error number PCRE_ERROR_CALLOUT is 4517 reserved for use by callout functions; it will never be used by PCRE 4518 itself. 4519 4520 4521AUTHOR 4522 4523 Philip Hazel 4524 University Computing Service 4525 Cambridge CB2 3QH, England. 4526 4527 4528REVISION 4529 4530 Last updated: 12 November 2013 4531 Copyright (c) 1997-2013 University of Cambridge. 4532------------------------------------------------------------------------------ 4533 4534 4535PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3) 4536 4537 4538 4539NAME 4540 PCRE - Perl-compatible regular expressions 4541 4542DIFFERENCES BETWEEN PCRE AND PERL 4543 4544 This document describes the differences in the ways that PCRE and Perl 4545 handle regular expressions. The differences described here are with 4546 respect to Perl versions 5.10 and above. 4547 4548 1. PCRE has only a subset of Perl's Unicode support. Details of what it 4549 does have are given in the pcreunicode page. 4550 4551 2. PCRE allows repeat quantifiers only on parenthesized assertions, but 4552 they do not mean what you might think. For example, (?!a){3} does not 4553 assert that the next three characters are not "a". It just asserts that 4554 the next character is not "a" three times (in principle: PCRE optimizes 4555 this to run the assertion just once). Perl allows repeat quantifiers on 4556 other assertions such as \b, but these do not seem to have any use. 4557 4558 3. Capturing subpatterns that occur inside negative lookahead asser- 4559 tions are counted, but their entries in the offsets vector are never 4560 set. Perl sometimes (but not always) sets its numerical variables from 4561 inside negative assertions. 4562 4563 4. Though binary zero characters are supported in the subject string, 4564 they are not allowed in a pattern string because it is passed as a nor- 4565 mal C string, terminated by zero. The escape sequence \0 can be used in 4566 the pattern to represent a binary zero. 4567 4568 5. The following Perl escape sequences are not supported: \l, \u, \L, 4569 \U, and \N when followed by a character name or Unicode value. (\N on 4570 its own, matching a non-newline character, is supported.) In fact these 4571 are implemented by Perl's general string-handling and are not part of 4572 its pattern matching engine. If any of these are encountered by PCRE, 4573 an error is generated by default. However, if the PCRE_JAVASCRIPT_COM- 4574 PAT option is set, \U and \u are interpreted as JavaScript interprets 4575 them. 4576 4577 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE 4578 is built with Unicode character property support. The properties that 4579 can be tested with \p and \P are limited to the general category prop- 4580 erties such as Lu and Nd, script names such as Greek or Han, and the 4581 derived properties Any and L&. PCRE does support the Cs (surrogate) 4582 property, which Perl does not; the Perl documentation says "Because 4583 Perl hides the need for the user to understand the internal representa- 4584 tion of Unicode characters, there is no need to implement the somewhat 4585 messy concept of surrogates." 4586 4587 7. PCRE does support the \Q...\E escape for quoting substrings. Charac- 4588 ters in between are treated as literals. This is slightly different 4589 from Perl in that $ and @ are also handled as literals inside the 4590 quotes. In Perl, they cause variable interpolation (but of course PCRE 4591 does not have variables). Note the following examples: 4592 4593 Pattern PCRE matches Perl matches 4594 4595 \Qabc$xyz\E abc$xyz abc followed by the 4596 contents of $xyz 4597 \Qabc\$xyz\E abc\$xyz abc\$xyz 4598 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz 4599 4600 The \Q...\E sequence is recognized both inside and outside character 4601 classes. 4602 4603 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) 4604 constructions. However, there is support for recursive patterns. This 4605 is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE 4606 "callout" feature allows an external function to be called during pat- 4607 tern matching. See the pcrecallout documentation for details. 4608 4609 9. Subpatterns that are called as subroutines (whether or not recur- 4610 sively) are always treated as atomic groups in PCRE. This is like 4611 Python, but unlike Perl. Captured values that are set outside a sub- 4612 routine call can be reference from inside in PCRE, but not in Perl. 4613 There is a discussion that explains these differences in more detail in 4614 the section on recursion differences from Perl in the pcrepattern page. 4615 4616 10. If any of the backtracking control verbs are used in a subpattern 4617 that is called as a subroutine (whether or not recursively), their 4618 effect is confined to that subpattern; it does not extend to the sur- 4619 rounding pattern. This is not always the case in Perl. In particular, 4620 if (*THEN) is present in a group that is called as a subroutine, its 4621 action is limited to that group, even if the group does not contain any 4622 | characters. Note that such subpatterns are processed as anchored at 4623 the point where they are tested. 4624 4625 11. If a pattern contains more than one backtracking control verb, the 4626 first one that is backtracked onto acts. For example, in the pattern 4627 A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure 4628 in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases 4629 it is the same as PCRE, but there are examples where it differs. 4630 4631 12. Most backtracking verbs in assertions have their normal actions. 4632 They are not confined to the assertion. 4633 4634 13. There are some differences that are concerned with the settings of 4635 captured strings when part of a pattern is repeated. For example, 4636 matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 4637 unset, but in PCRE it is set to "b". 4638 4639 14. PCRE's handling of duplicate subpattern numbers and duplicate sub- 4640 pattern names is not as general as Perl's. This is a consequence of the 4641 fact the PCRE works internally just with numbers, using an external ta- 4642 ble to translate between numbers and names. In particular, a pattern 4643 such as (?|(?<a>A)|(?<b>B), where the two capturing parentheses have 4644 the same number but different names, is not supported, and causes an 4645 error at compile time. If it were allowed, it would not be possible to 4646 distinguish which parentheses matched, because both names map to cap- 4647 turing subpattern number 1. To avoid this confusing situation, an error 4648 is given at compile time. 4649 4650 15. Perl recognizes comments in some places that PCRE does not, for 4651 example, between the ( and ? at the start of a subpattern. If the /x 4652 modifier is set, Perl allows white space between ( and ? (though cur- 4653 rent Perls warn that this is deprecated) but PCRE never does, even if 4654 the PCRE_EXTENDED option is set. 4655 4656 16. Perl, when in warning mode, gives warnings for character classes 4657 such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter- 4658 als. PCRE has no warning features, so it gives an error in these cases 4659 because they are almost certainly user mistakes. 4660 4661 17. In PCRE, the upper/lower case character properties Lu and Ll are 4662 not affected when case-independent matching is specified. For example, 4663 \p{Lu} always matches an upper case letter. I think Perl has changed in 4664 this respect; in the release at the time of writing (5.16), \p{Lu} and 4665 \p{Ll} match all letters, regardless of case, when case independence is 4666 specified. 4667 4668 18. PCRE provides some extensions to the Perl regular expression facil- 4669 ities. Perl 5.10 includes new features that are not in earlier ver- 4670 sions of Perl, some of which (such as named parentheses) have been in 4671 PCRE for some time. This list is with respect to Perl 5.10: 4672 4673 (a) Although lookbehind assertions in PCRE must match fixed length 4674 strings, each alternative branch of a lookbehind assertion can match a 4675 different length of string. Perl requires them all to have the same 4676 length. 4677 4678 (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $ 4679 meta-character matches only at the very end of the string. 4680 4681 (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe- 4682 cial meaning is faulted. Otherwise, like Perl, the backslash is quietly 4683 ignored. (Perl can be made to issue a warning.) 4684 4685 (d) If PCRE_UNGREEDY is set, the greediness of the repetition quanti- 4686 fiers is inverted, that is, by default they are not greedy, but if fol- 4687 lowed by a question mark they are. 4688 4689 (e) PCRE_ANCHORED can be used at matching time to force a pattern to be 4690 tried only at the first matching position in the subject string. 4691 4692 (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, 4693 and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no Perl equiva- 4694 lents. 4695 4696 (g) The \R escape sequence can be restricted to match only CR, LF, or 4697 CRLF by the PCRE_BSR_ANYCRLF option. 4698 4699 (h) The callout facility is PCRE-specific. 4700 4701 (i) The partial matching facility is PCRE-specific. 4702 4703 (j) Patterns compiled by PCRE can be saved and re-used at a later time, 4704 even on different hosts that have the other endianness. However, this 4705 does not apply to optimized data created by the just-in-time compiler. 4706 4707 (k) The alternative matching functions (pcre_dfa_exec(), 4708 pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and 4709 are not Perl-compatible. 4710 4711 (l) PCRE recognizes some special sequences such as (*CR) at the start 4712 of a pattern that set overall options that cannot be changed within the 4713 pattern. 4714 4715 4716AUTHOR 4717 4718 Philip Hazel 4719 University Computing Service 4720 Cambridge CB2 3QH, England. 4721 4722 4723REVISION 4724 4725 Last updated: 10 November 2013 4726 Copyright (c) 1997-2013 University of Cambridge. 4727------------------------------------------------------------------------------ 4728 4729 4730PCREPATTERN(3) Library Functions Manual PCREPATTERN(3) 4731 4732 4733 4734NAME 4735 PCRE - Perl-compatible regular expressions 4736 4737PCRE REGULAR EXPRESSION DETAILS 4738 4739 The syntax and semantics of the regular expressions that are supported 4740 by PCRE are described in detail below. There is a quick-reference syn- 4741 tax summary in the pcresyntax page. PCRE tries to match Perl syntax and 4742 semantics as closely as it can. PCRE also supports some alternative 4743 regular expression syntax (which does not conflict with the Perl syn- 4744 tax) in order to provide some compatibility with regular expressions in 4745 Python, .NET, and Oniguruma. 4746 4747 Perl's regular expressions are described in its own documentation, and 4748 regular expressions in general are covered in a number of books, some 4749 of which have copious examples. Jeffrey Friedl's "Mastering Regular 4750 Expressions", published by O'Reilly, covers regular expressions in 4751 great detail. This description of PCRE's regular expressions is 4752 intended as reference material. 4753 4754 This document discusses the patterns that are supported by PCRE when 4755 one its main matching functions, pcre_exec() (8-bit) or 4756 pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has alternative 4757 matching functions, pcre_dfa_exec() and pcre[16|32_dfa_exec(), which 4758 match using a different algorithm that is not Perl-compatible. Some of 4759 the features discussed below are not available when DFA matching is 4760 used. The advantages and disadvantages of the alternative functions, 4761 and how they differ from the normal functions, are discussed in the 4762 pcrematching page. 4763 4764 4765SPECIAL START-OF-PATTERN ITEMS 4766 4767 A number of options that can be passed to pcre_compile() can also be 4768 set by special items at the start of a pattern. These are not Perl-com- 4769 patible, but are provided to make these options accessible to pattern 4770 writers who are not able to change the program that processes the pat- 4771 tern. Any number of these items may appear, but they must all be 4772 together right at the start of the pattern string, and the letters must 4773 be in upper case. 4774 4775 UTF support 4776 4777 The original operation of PCRE was on strings of one-byte characters. 4778 However, there is now also support for UTF-8 strings in the original 4779 library, an extra library that supports 16-bit and UTF-16 character 4780 strings, and a third library that supports 32-bit and UTF-32 character 4781 strings. To use these features, PCRE must be built to include appropri- 4782 ate support. When using UTF strings you must either call the compiling 4783 function with the PCRE_UTF8, PCRE_UTF16, or PCRE_UTF32 option, or the 4784 pattern must start with one of these special sequences: 4785 4786 (*UTF8) 4787 (*UTF16) 4788 (*UTF32) 4789 (*UTF) 4790 4791 (*UTF) is a generic sequence that can be used with any of the 4792 libraries. Starting a pattern with such a sequence is equivalent to 4793 setting the relevant option. How setting a UTF mode affects pattern 4794 matching is mentioned in several places below. There is also a summary 4795 of features in the pcreunicode page. 4796 4797 Some applications that allow their users to supply patterns may wish to 4798 restrict them to non-UTF data for security reasons. If the 4799 PCRE_NEVER_UTF option is set at compile time, (*UTF) etc. are not 4800 allowed, and their appearance causes an error. 4801 4802 Unicode property support 4803 4804 Another special sequence that may appear at the start of a pattern is 4805 (*UCP). This has the same effect as setting the PCRE_UCP option: it 4806 causes sequences such as \d and \w to use Unicode properties to deter- 4807 mine character types, instead of recognizing only characters with codes 4808 less than 128 via a lookup table. 4809 4810 Disabling auto-possessification 4811 4812 If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as 4813 setting the PCRE_NO_AUTO_POSSESS option at compile time. This stops 4814 PCRE from making quantifiers possessive when what follows cannot match 4815 the repeated item. For example, by default a+b is treated as a++b. For 4816 more details, see the pcreapi documentation. 4817 4818 Disabling start-up optimizations 4819 4820 If a pattern starts with (*NO_START_OPT), it has the same effect as 4821 setting the PCRE_NO_START_OPTIMIZE option either at compile or matching 4822 time. This disables several optimizations for quickly reaching "no 4823 match" results. For more details, see the pcreapi documentation. 4824 4825 Newline conventions 4826 4827 PCRE supports five different conventions for indicating line breaks in 4828 strings: a single CR (carriage return) character, a single LF (line- 4829 feed) character, the two-character sequence CRLF, any of the three pre- 4830 ceding, or any Unicode newline sequence. The pcreapi page has further 4831 discussion about newlines, and shows how to set the newline convention 4832 in the options arguments for the compiling and matching functions. 4833 4834 It is also possible to specify a newline convention by starting a pat- 4835 tern string with one of the following five sequences: 4836 4837 (*CR) carriage return 4838 (*LF) linefeed 4839 (*CRLF) carriage return, followed by linefeed 4840 (*ANYCRLF) any of the three above 4841 (*ANY) all Unicode newline sequences 4842 4843 These override the default and the options given to the compiling func- 4844 tion. For example, on a Unix system where LF is the default newline 4845 sequence, the pattern 4846 4847 (*CR)a.b 4848 4849 changes the convention to CR. That pattern matches "a\nb" because LF is 4850 no longer a newline. If more than one of these settings is present, the 4851 last one is used. 4852 4853 The newline convention affects where the circumflex and dollar asser- 4854 tions are true. It also affects the interpretation of the dot metachar- 4855 acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it 4856 does not affect what the \R escape sequence matches. By default, this 4857 is any Unicode newline sequence, for Perl compatibility. However, this 4858 can be changed; see the description of \R in the section entitled "New- 4859 line sequences" below. A change of \R setting can be combined with a 4860 change of newline convention. 4861 4862 Setting match and recursion limits 4863 4864 The caller of pcre_exec() can set a limit on the number of times the 4865 internal match() function is called and on the maximum depth of recur- 4866 sive calls. These facilities are provided to catch runaway matches that 4867 are provoked by patterns with huge matching trees (a typical example is 4868 a pattern with nested unlimited repeats) and to avoid running out of 4869 system stack by too much recursion. When one of these limits is 4870 reached, pcre_exec() gives an error return. The limits can also be set 4871 by items at the start of the pattern of the form 4872 4873 (*LIMIT_MATCH=d) 4874 (*LIMIT_RECURSION=d) 4875 4876 where d is any number of decimal digits. However, the value of the set- 4877 ting must be less than the value set (or defaulted) by the caller of 4878 pcre_exec() for it to have any effect. In other words, the pattern 4879 writer can lower the limits set by the programmer, but not raise them. 4880 If there is more than one setting of one of these limits, the lower 4881 value is used. 4882 4883 4884EBCDIC CHARACTER CODES 4885 4886 PCRE can be compiled to run in an environment that uses EBCDIC as its 4887 character code rather than ASCII or Unicode (typically a mainframe sys- 4888 tem). In the sections below, character code values are ASCII or Uni- 4889 code; in an EBCDIC environment these characters may have different code 4890 values, and there are no code points greater than 255. 4891 4892 4893CHARACTERS AND METACHARACTERS 4894 4895 A regular expression is a pattern that is matched against a subject 4896 string from left to right. Most characters stand for themselves in a 4897 pattern, and match the corresponding characters in the subject. As a 4898 trivial example, the pattern 4899 4900 The quick brown fox 4901 4902 matches a portion of a subject string that is identical to itself. When 4903 caseless matching is specified (the PCRE_CASELESS option), letters are 4904 matched independently of case. In a UTF mode, PCRE always understands 4905 the concept of case for characters whose values are less than 128, so 4906 caseless matching is always possible. For characters with higher val- 4907 ues, the concept of case is supported if PCRE is compiled with Unicode 4908 property support, but not otherwise. If you want to use caseless 4909 matching for characters 128 and above, you must ensure that PCRE is 4910 compiled with Unicode property support as well as with UTF support. 4911 4912 The power of regular expressions comes from the ability to include 4913 alternatives and repetitions in the pattern. These are encoded in the 4914 pattern by the use of metacharacters, which do not stand for themselves 4915 but instead are interpreted in some special way. 4916 4917 There are two different sets of metacharacters: those that are recog- 4918 nized anywhere in the pattern except within square brackets, and those 4919 that are recognized within square brackets. Outside square brackets, 4920 the metacharacters are as follows: 4921 4922 \ general escape character with several uses 4923 ^ assert start of string (or line, in multiline mode) 4924 $ assert end of string (or line, in multiline mode) 4925 . match any character except newline (by default) 4926 [ start character class definition 4927 | start of alternative branch 4928 ( start subpattern 4929 ) end subpattern 4930 ? extends the meaning of ( 4931 also 0 or 1 quantifier 4932 also quantifier minimizer 4933 * 0 or more quantifier 4934 + 1 or more quantifier 4935 also "possessive quantifier" 4936 { start min/max quantifier 4937 4938 Part of a pattern that is in square brackets is called a "character 4939 class". In a character class the only metacharacters are: 4940 4941 \ general escape character 4942 ^ negate the class, but only if the first character 4943 - indicates character range 4944 [ POSIX character class (only if followed by POSIX 4945 syntax) 4946 ] terminates the character class 4947 4948 The following sections describe the use of each of the metacharacters. 4949 4950 4951BACKSLASH 4952 4953 The backslash character has several uses. Firstly, if it is followed by 4954 a character that is not a number or a letter, it takes away any special 4955 meaning that character may have. This use of backslash as an escape 4956 character applies both inside and outside character classes. 4957 4958 For example, if you want to match a * character, you write \* in the 4959 pattern. This escaping action applies whether or not the following 4960 character would otherwise be interpreted as a metacharacter, so it is 4961 always safe to precede a non-alphanumeric with backslash to specify 4962 that it stands for itself. In particular, if you want to match a back- 4963 slash, you write \\. 4964 4965 In a UTF mode, only ASCII numbers and letters have any special meaning 4966 after a backslash. All other characters (in particular, those whose 4967 codepoints are greater than 127) are treated as literals. 4968 4969 If a pattern is compiled with the PCRE_EXTENDED option, most white 4970 space in the pattern (other than in a character class), and characters 4971 between a # outside a character class and the next newline, inclusive, 4972 are ignored. An escaping backslash can be used to include a white space 4973 or # character as part of the pattern. 4974 4975 If you want to remove the special meaning from a sequence of charac- 4976 ters, you can do so by putting them between \Q and \E. This is differ- 4977 ent from Perl in that $ and @ are handled as literals in \Q...\E 4978 sequences in PCRE, whereas in Perl, $ and @ cause variable interpola- 4979 tion. Note the following examples: 4980 4981 Pattern PCRE matches Perl matches 4982 4983 \Qabc$xyz\E abc$xyz abc followed by the 4984 contents of $xyz 4985 \Qabc\$xyz\E abc\$xyz abc\$xyz 4986 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz 4987 4988 The \Q...\E sequence is recognized both inside and outside character 4989 classes. An isolated \E that is not preceded by \Q is ignored. If \Q 4990 is not followed by \E later in the pattern, the literal interpretation 4991 continues to the end of the pattern (that is, \E is assumed at the 4992 end). If the isolated \Q is inside a character class, this causes an 4993 error, because the character class is not terminated. 4994 4995 Non-printing characters 4996 4997 A second use of backslash provides a way of encoding non-printing char- 4998 acters in patterns in a visible manner. There is no restriction on the 4999 appearance of non-printing characters, apart from the binary zero that 5000 terminates a pattern, but when a pattern is being prepared by text 5001 editing, it is often easier to use one of the following escape 5002 sequences than the binary character it represents. In an ASCII or Uni- 5003 code environment, these escapes are as follows: 5004 5005 \a alarm, that is, the BEL character (hex 07) 5006 \cx "control-x", where x is any ASCII character 5007 \e escape (hex 1B) 5008 \f form feed (hex 0C) 5009 \n linefeed (hex 0A) 5010 \r carriage return (hex 0D) 5011 \t tab (hex 09) 5012 \0dd character with octal code 0dd 5013 \ddd character with octal code ddd, or back reference 5014 \o{ddd..} character with octal code ddd.. 5015 \xhh character with hex code hh 5016 \x{hhh..} character with hex code hhh.. (non-JavaScript mode) 5017 \uhhhh character with hex code hhhh (JavaScript mode only) 5018 5019 The precise effect of \cx on ASCII characters is as follows: if x is a 5020 lower case letter, it is converted to upper case. Then bit 6 of the 5021 character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A 5022 (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes 5023 hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c 5024 has a value greater than 127, a compile-time error occurs. This locks 5025 out non-ASCII characters in all modes. 5026 5027 When PCRE is compiled in EBCDIC mode, \a, \e, \f, \n, \r, and \t gener- 5028 ate the appropriate EBCDIC code values. The \c escape is processed as 5029 specified for Perl in the perlebcdic document. The only characters that 5030 are allowed after \c are A-Z, a-z, or one of @, [, \, ], ^, _, or ?. 5031 Any other character provokes a compile-time error. The sequence \c@ 5032 encodes character code 0; after \c the letters (in either case) encode 5033 characters 1-26 (hex 01 to hex 1A); [, \, ], ^, and _ encode characters 5034 27-31 (hex 1B to hex 1F), and \c? becomes either 255 (hex FF) or 95 5035 (hex 5F). 5036 5037 Thus, apart from \c?, these escapes generate the same character code 5038 values as they do in an ASCII environment, though the meanings of the 5039 values mostly differ. For example, \cG always generates code value 7, 5040 which is BEL in ASCII but DEL in EBCDIC. 5041 5042 The sequence \c? generates DEL (127, hex 7F) in an ASCII environment, 5043 but because 127 is not a control character in EBCDIC, Perl makes it 5044 generate the APC character. Unfortunately, there are several variants 5045 of EBCDIC. In most of them the APC character has the value 255 (hex 5046 FF), but in the one Perl calls POSIX-BC its value is 95 (hex 5F). If 5047 certain other characters have POSIX-BC values, PCRE makes \c? generate 5048 95; otherwise it generates 255. 5049 5050 After \0 up to two further octal digits are read. If there are fewer 5051 than two digits, just those that are present are used. Thus the 5052 sequence \0\x\015 specifies two binary zeros followed by a CR character 5053 (code value 13). Make sure you supply two digits after the initial zero 5054 if the pattern character that follows is itself an octal digit. 5055 5056 The escape \o must be followed by a sequence of octal digits, enclosed 5057 in braces. An error occurs if this is not the case. This escape is a 5058 recent addition to Perl; it provides way of specifying character code 5059 points as octal numbers greater than 0777, and it also allows octal 5060 numbers and back references to be unambiguously specified. 5061 5062 For greater clarity and unambiguity, it is best to avoid following \ by 5063 a digit greater than zero. Instead, use \o{} or \x{} to specify charac- 5064 ter numbers, and \g{} to specify back references. The following para- 5065 graphs describe the old, ambiguous syntax. 5066 5067 The handling of a backslash followed by a digit other than 0 is compli- 5068 cated, and Perl has changed in recent releases, causing PCRE also to 5069 change. Outside a character class, PCRE reads the digit and any follow- 5070 ing digits as a decimal number. If the number is less than 8, or if 5071 there have been at least that many previous capturing left parentheses 5072 in the expression, the entire sequence is taken as a back reference. A 5073 description of how this works is given later, following the discussion 5074 of parenthesized subpatterns. 5075 5076 Inside a character class, or if the decimal number following \ is 5077 greater than 7 and there have not been that many capturing subpatterns, 5078 PCRE handles \8 and \9 as the literal characters "8" and "9", and oth- 5079 erwise re-reads up to three octal digits following the backslash, using 5080 them to generate a data character. Any subsequent digits stand for 5081 themselves. For example: 5082 5083 \040 is another way of writing an ASCII space 5084 \40 is the same, provided there are fewer than 40 5085 previous capturing subpatterns 5086 \7 is always a back reference 5087 \11 might be a back reference, or another way of 5088 writing a tab 5089 \011 is always a tab 5090 \0113 is a tab followed by the character "3" 5091 \113 might be a back reference, otherwise the 5092 character with octal code 113 5093 \377 might be a back reference, otherwise 5094 the value 255 (decimal) 5095 \81 is either a back reference, or the two 5096 characters "8" and "1" 5097 5098 Note that octal values of 100 or greater that are specified using this 5099 syntax must not be introduced by a leading zero, because no more than 5100 three octal digits are ever read. 5101 5102 By default, after \x that is not followed by {, from zero to two hexa- 5103 decimal digits are read (letters can be in upper or lower case). Any 5104 number of hexadecimal digits may appear between \x{ and }. If a charac- 5105 ter other than a hexadecimal digit appears between \x{ and }, or if 5106 there is no terminating }, an error occurs. 5107 5108 If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x 5109 is as just described only when it is followed by two hexadecimal dig- 5110 its. Otherwise, it matches a literal "x" character. In JavaScript 5111 mode, support for code points greater than 256 is provided by \u, which 5112 must be followed by four hexadecimal digits; otherwise it matches a 5113 literal "u" character. 5114 5115 Characters whose value is less than 256 can be defined by either of the 5116 two syntaxes for \x (or by \u in JavaScript mode). There is no differ- 5117 ence in the way they are handled. For example, \xdc is exactly the same 5118 as \x{dc} (or \u00dc in JavaScript mode). 5119 5120 Constraints on character values 5121 5122 Characters that are specified using octal or hexadecimal numbers are 5123 limited to certain values, as follows: 5124 5125 8-bit non-UTF mode less than 0x100 5126 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint 5127 16-bit non-UTF mode less than 0x10000 5128 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint 5129 32-bit non-UTF mode less than 0x100000000 5130 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint 5131 5132 Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- 5133 called "surrogate" codepoints), and 0xffef. 5134 5135 Escape sequences in character classes 5136 5137 All the sequences that define a single character value can be used both 5138 inside and outside character classes. In addition, inside a character 5139 class, \b is interpreted as the backspace character (hex 08). 5140 5141 \N is not allowed in a character class. \B, \R, and \X are not special 5142 inside a character class. Like other unrecognized escape sequences, 5143 they are treated as the literal characters "B", "R", and "X" by 5144 default, but cause an error if the PCRE_EXTRA option is set. Outside a 5145 character class, these sequences have different meanings. 5146 5147 Unsupported escape sequences 5148 5149 In Perl, the sequences \l, \L, \u, and \U are recognized by its string 5150 handler and used to modify the case of following characters. By 5151 default, PCRE does not support these escape sequences. However, if the 5152 PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and 5153 \u can be used to define a character by code point, as described in the 5154 previous section. 5155 5156 Absolute and relative back references 5157 5158 The sequence \g followed by an unsigned or a negative number, option- 5159 ally enclosed in braces, is an absolute or relative back reference. A 5160 named back reference can be coded as \g{name}. Back references are dis- 5161 cussed later, following the discussion of parenthesized subpatterns. 5162 5163 Absolute and relative subroutine calls 5164 5165 For compatibility with Oniguruma, the non-Perl syntax \g followed by a 5166 name or a number enclosed either in angle brackets or single quotes, is 5167 an alternative syntax for referencing a subpattern as a "subroutine". 5168 Details are discussed later. Note that \g{...} (Perl syntax) and 5169 \g<...> (Oniguruma syntax) are not synonymous. The former is a back 5170 reference; the latter is a subroutine call. 5171 5172 Generic character types 5173 5174 Another use of backslash is for specifying generic character types: 5175 5176 \d any decimal digit 5177 \D any character that is not a decimal digit 5178 \h any horizontal white space character 5179 \H any character that is not a horizontal white space character 5180 \s any white space character 5181 \S any character that is not a white space character 5182 \v any vertical white space character 5183 \V any character that is not a vertical white space character 5184 \w any "word" character 5185 \W any "non-word" character 5186 5187 There is also the single sequence \N, which matches a non-newline char- 5188 acter. This is the same as the "." metacharacter when PCRE_DOTALL is 5189 not set. Perl also uses \N to match characters by name; PCRE does not 5190 support this. 5191 5192 Each pair of lower and upper case escape sequences partitions the com- 5193 plete set of characters into two disjoint sets. Any given character 5194 matches one, and only one, of each pair. The sequences can appear both 5195 inside and outside character classes. They each match one character of 5196 the appropriate type. If the current matching point is at the end of 5197 the subject string, all of them fail, because there is no character to 5198 match. 5199 5200 For compatibility with Perl, \s did not used to match the VT character 5201 (code 11), which made it different from the the POSIX "space" class. 5202 However, Perl added VT at release 5.18, and PCRE followed suit at 5203 release 8.34. The default \s characters are now HT (9), LF (10), VT 5204 (11), FF (12), CR (13), and space (32), which are defined as white 5205 space in the "C" locale. This list may vary if locale-specific matching 5206 is taking place. For example, in some locales the "non-breaking space" 5207 character (\xA0) is recognized as white space, and in others the VT 5208 character is not. 5209 5210 A "word" character is an underscore or any character that is a letter 5211 or digit. By default, the definition of letters and digits is con- 5212 trolled by PCRE's low-valued character tables, and may vary if locale- 5213 specific matching is taking place (see "Locale support" in the pcreapi 5214 page). For example, in a French locale such as "fr_FR" in Unix-like 5215 systems, or "french" in Windows, some character codes greater than 127 5216 are used for accented letters, and these are then matched by \w. The 5217 use of locales with Unicode is discouraged. 5218 5219 By default, characters whose code points are greater than 127 never 5220 match \d, \s, or \w, and always match \D, \S, and \W, although this may 5221 vary for characters in the range 128-255 when locale-specific matching 5222 is happening. These escape sequences retain their original meanings 5223 from before Unicode support was available, mainly for efficiency rea- 5224 sons. If PCRE is compiled with Unicode property support, and the 5225 PCRE_UCP option is set, the behaviour is changed so that Unicode prop- 5226 erties are used to determine character types, as follows: 5227 5228 \d any character that matches \p{Nd} (decimal digit) 5229 \s any character that matches \p{Z} or \h or \v 5230 \w any character that matches \p{L} or \p{N}, plus underscore 5231 5232 The upper case escapes match the inverse sets of characters. Note that 5233 \d matches only decimal digits, whereas \w matches any Unicode digit, 5234 as well as any Unicode letter, and underscore. Note also that PCRE_UCP 5235 affects \b, and \B because they are defined in terms of \w and \W. 5236 Matching these sequences is noticeably slower when PCRE_UCP is set. 5237 5238 The sequences \h, \H, \v, and \V are features that were added to Perl 5239 at release 5.10. In contrast to the other sequences, which match only 5240 ASCII characters by default, these always match certain high-valued 5241 code points, whether or not PCRE_UCP is set. The horizontal space char- 5242 acters are: 5243 5244 U+0009 Horizontal tab (HT) 5245 U+0020 Space 5246 U+00A0 Non-break space 5247 U+1680 Ogham space mark 5248 U+180E Mongolian vowel separator 5249 U+2000 En quad 5250 U+2001 Em quad 5251 U+2002 En space 5252 U+2003 Em space 5253 U+2004 Three-per-em space 5254 U+2005 Four-per-em space 5255 U+2006 Six-per-em space 5256 U+2007 Figure space 5257 U+2008 Punctuation space 5258 U+2009 Thin space 5259 U+200A Hair space 5260 U+202F Narrow no-break space 5261 U+205F Medium mathematical space 5262 U+3000 Ideographic space 5263 5264 The vertical space characters are: 5265 5266 U+000A Linefeed (LF) 5267 U+000B Vertical tab (VT) 5268 U+000C Form feed (FF) 5269 U+000D Carriage return (CR) 5270 U+0085 Next line (NEL) 5271 U+2028 Line separator 5272 U+2029 Paragraph separator 5273 5274 In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 5275 256 are relevant. 5276 5277 Newline sequences 5278 5279 Outside a character class, by default, the escape sequence \R matches 5280 any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent 5281 to the following: 5282 5283 (?>\r\n|\n|\x0b|\f|\r|\x85) 5284 5285 This is an example of an "atomic group", details of which are given 5286 below. This particular group matches either the two-character sequence 5287 CR followed by LF, or one of the single characters LF (linefeed, 5288 U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car- 5289 riage return, U+000D), or NEL (next line, U+0085). The two-character 5290 sequence is treated as a single unit that cannot be split. 5291 5292 In other modes, two additional characters whose codepoints are greater 5293 than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa- 5294 rator, U+2029). Unicode character property support is not needed for 5295 these characters to be recognized. 5296 5297 It is possible to restrict \R to match only CR, LF, or CRLF (instead of 5298 the complete set of Unicode line endings) by setting the option 5299 PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched. 5300 (BSR is an abbrevation for "backslash R".) This can be made the default 5301 when PCRE is built; if this is the case, the other behaviour can be 5302 requested via the PCRE_BSR_UNICODE option. It is also possible to 5303 specify these settings by starting a pattern string with one of the 5304 following sequences: 5305 5306 (*BSR_ANYCRLF) CR, LF, or CRLF only 5307 (*BSR_UNICODE) any Unicode newline sequence 5308 5309 These override the default and the options given to the compiling func- 5310 tion, but they can themselves be overridden by options given to a 5311 matching function. Note that these special settings, which are not 5312 Perl-compatible, are recognized only at the very start of a pattern, 5313 and that they must be in upper case. If more than one of them is 5314 present, the last one is used. They can be combined with a change of 5315 newline convention; for example, a pattern can start with: 5316 5317 (*ANY)(*BSR_ANYCRLF) 5318 5319 They can also be combined with the (*UTF8), (*UTF16), (*UTF32), (*UTF) 5320 or (*UCP) special sequences. Inside a character class, \R is treated as 5321 an unrecognized escape sequence, and so matches the letter "R" by 5322 default, but causes an error if PCRE_EXTRA is set. 5323 5324 Unicode character properties 5325 5326 When PCRE is built with Unicode character property support, three addi- 5327 tional escape sequences that match characters with specific properties 5328 are available. When in 8-bit non-UTF-8 mode, these sequences are of 5329 course limited to testing characters whose codepoints are less than 5330 256, but they do work in this mode. The extra escape sequences are: 5331 5332 \p{xx} a character with the xx property 5333 \P{xx} a character without the xx property 5334 \X a Unicode extended grapheme cluster 5335 5336 The property names represented by xx above are limited to the Unicode 5337 script names, the general category properties, "Any", which matches any 5338 character (including newline), and some special PCRE properties 5339 (described in the next section). Other Perl properties such as "InMu- 5340 sicalSymbols" are not currently supported by PCRE. Note that \P{Any} 5341 does not match any characters, so always causes a match failure. 5342 5343 Sets of Unicode characters are defined as belonging to certain scripts. 5344 A character from one of these sets can be matched using a script name. 5345 For example: 5346 5347 \p{Greek} 5348 \P{Han} 5349 5350 Those that are not part of an identified script are lumped together as 5351 "Common". The current list of scripts is: 5352 5353 Arabic, Armenian, Avestan, Balinese, Bamum, Bassa_Vah, Batak, Bengali, 5354 Bopomofo, Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Car- 5355 ian, Caucasian_Albanian, Chakma, Cham, Cherokee, Common, Coptic, Cunei- 5356 form, Cypriot, Cyrillic, Deseret, Devanagari, Duployan, Egyptian_Hiero- 5357 glyphs, Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha, 5358 Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, 5359 Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- 5360 tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, 5361 Kharoshthi, Khmer, Khojki, Khudawadi, Lao, Latin, Lepcha, Limbu, Lin- 5362 ear_A, Linear_B, Lisu, Lycian, Lydian, Mahajani, Malayalam, Mandaic, 5363 Manichaean, Meetei_Mayek, Mende_Kikakui, Meroitic_Cursive, 5364 Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro, Myanmar, Nabataean, 5365 New_Tai_Lue, Nko, Ogham, Ol_Chiki, Old_Italic, Old_North_Arabian, 5366 Old_Permic, Old_Persian, Old_South_Arabian, Old_Turkic, Oriya, Osmanya, 5367 Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, Phoenician, 5368 Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Sha- 5369 vian, Siddham, Sinhala, Sora_Sompeng, Sundanese, Syloti_Nagri, Syriac, 5370 Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, Takri, Tamil, Telugu, 5371 Thaana, Thai, Tibetan, Tifinagh, Tirhuta, Ugaritic, Vai, Warang_Citi, 5372 Yi. 5373 5374 Each character has exactly one Unicode general category property, spec- 5375 ified by a two-letter abbreviation. For compatibility with Perl, nega- 5376 tion can be specified by including a circumflex between the opening 5377 brace and the property name. For example, \p{^Lu} is the same as 5378 \P{Lu}. 5379 5380 If only one letter is specified with \p or \P, it includes all the gen- 5381 eral category properties that start with that letter. In this case, in 5382 the absence of negation, the curly brackets in the escape sequence are 5383 optional; these two examples have the same effect: 5384 5385 \p{L} 5386 \pL 5387 5388 The following general category property codes are supported: 5389 5390 C Other 5391 Cc Control 5392 Cf Format 5393 Cn Unassigned 5394 Co Private use 5395 Cs Surrogate 5396 5397 L Letter 5398 Ll Lower case letter 5399 Lm Modifier letter 5400 Lo Other letter 5401 Lt Title case letter 5402 Lu Upper case letter 5403 5404 M Mark 5405 Mc Spacing mark 5406 Me Enclosing mark 5407 Mn Non-spacing mark 5408 5409 N Number 5410 Nd Decimal number 5411 Nl Letter number 5412 No Other number 5413 5414 P Punctuation 5415 Pc Connector punctuation 5416 Pd Dash punctuation 5417 Pe Close punctuation 5418 Pf Final punctuation 5419 Pi Initial punctuation 5420 Po Other punctuation 5421 Ps Open punctuation 5422 5423 S Symbol 5424 Sc Currency symbol 5425 Sk Modifier symbol 5426 Sm Mathematical symbol 5427 So Other symbol 5428 5429 Z Separator 5430 Zl Line separator 5431 Zp Paragraph separator 5432 Zs Space separator 5433 5434 The special property L& is also supported: it matches a character that 5435 has the Lu, Ll, or Lt property, in other words, a letter that is not 5436 classified as a modifier or "other". 5437 5438 The Cs (Surrogate) property applies only to characters in the range 5439 U+D800 to U+DFFF. Such characters are not valid in Unicode strings and 5440 so cannot be tested by PCRE, unless UTF validity checking has been 5441 turned off (see the discussion of PCRE_NO_UTF8_CHECK, 5442 PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_CHECK in the pcreapi page). Perl 5443 does not support the Cs property. 5444 5445 The long synonyms for property names that Perl supports (such as 5446 \p{Letter}) are not supported by PCRE, nor is it permitted to prefix 5447 any of these properties with "Is". 5448 5449 No character that is in the Unicode table has the Cn (unassigned) prop- 5450 erty. Instead, this property is assumed for any code point that is not 5451 in the Unicode table. 5452 5453 Specifying caseless matching does not affect these escape sequences. 5454 For example, \p{Lu} always matches only upper case letters. This is 5455 different from the behaviour of current versions of Perl. 5456 5457 Matching characters by Unicode property is not fast, because PCRE has 5458 to do a multistage table lookup in order to find a character's prop- 5459 erty. That is why the traditional escape sequences such as \d and \w do 5460 not use Unicode properties in PCRE by default, though you can make them 5461 do so by setting the PCRE_UCP option or by starting the pattern with 5462 (*UCP). 5463 5464 Extended grapheme clusters 5465 5466 The \X escape matches any number of Unicode characters that form an 5467 "extended grapheme cluster", and treats the sequence as an atomic group 5468 (see below). Up to and including release 8.31, PCRE matched an ear- 5469 lier, simpler definition that was equivalent to 5470 5471 (?>\PM\pM*) 5472 5473 That is, it matched a character without the "mark" property, followed 5474 by zero or more characters with the "mark" property. Characters with 5475 the "mark" property are typically non-spacing accents that affect the 5476 preceding character. 5477 5478 This simple definition was extended in Unicode to include more compli- 5479 cated kinds of composite character by giving each character a grapheme 5480 breaking property, and creating rules that use these properties to 5481 define the boundaries of extended grapheme clusters. In releases of 5482 PCRE later than 8.31, \X matches one of these clusters. 5483 5484 \X always matches at least one character. Then it decides whether to 5485 add additional characters according to the following rules for ending a 5486 cluster: 5487 5488 1. End at the end of the subject string. 5489 5490 2. Do not end between CR and LF; otherwise end after any control char- 5491 acter. 5492 5493 3. Do not break Hangul (a Korean script) syllable sequences. Hangul 5494 characters are of five types: L, V, T, LV, and LVT. An L character may 5495 be followed by an L, V, LV, or LVT character; an LV or V character may 5496 be followed by a V or T character; an LVT or T character may be follwed 5497 only by a T character. 5498 5499 4. Do not end before extending characters or spacing marks. Characters 5500 with the "mark" property always have the "extend" grapheme breaking 5501 property. 5502 5503 5. Do not end after prepend characters. 5504 5505 6. Otherwise, end the cluster. 5506 5507 PCRE's additional properties 5508 5509 As well as the standard Unicode properties described above, PCRE sup- 5510 ports four more that make it possible to convert traditional escape 5511 sequences such as \w and \s to use Unicode properties. PCRE uses these 5512 non-standard, non-Perl properties internally when PCRE_UCP is set. How- 5513 ever, they may also be used explicitly. These properties are: 5514 5515 Xan Any alphanumeric character 5516 Xps Any POSIX space character 5517 Xsp Any Perl space character 5518 Xwd Any Perl "word" character 5519 5520 Xan matches characters that have either the L (letter) or the N (num- 5521 ber) property. Xps matches the characters tab, linefeed, vertical tab, 5522 form feed, or carriage return, and any other character that has the Z 5523 (separator) property. Xsp is the same as Xps; it used to exclude ver- 5524 tical tab, for Perl compatibility, but Perl changed, and so PCRE fol- 5525 lowed at release 8.34. Xwd matches the same characters as Xan, plus 5526 underscore. 5527 5528 There is another non-standard property, Xuc, which matches any charac- 5529 ter that can be represented by a Universal Character Name in C++ and 5530 other programming languages. These are the characters $, @, ` (grave 5531 accent), and all characters with Unicode code points greater than or 5532 equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that 5533 most base (ASCII) characters are excluded. (Universal Character Names 5534 are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit. 5535 Note that the Xuc property does not match these sequences but the char- 5536 acters that they represent.) 5537 5538 Resetting the match start 5539 5540 The escape sequence \K causes any previously matched characters not to 5541 be included in the final matched sequence. For example, the pattern: 5542 5543 foo\Kbar 5544 5545 matches "foobar", but reports that it has matched "bar". This feature 5546 is similar to a lookbehind assertion (described below). However, in 5547 this case, the part of the subject before the real match does not have 5548 to be of fixed length, as lookbehind assertions do. The use of \K does 5549 not interfere with the setting of captured substrings. For example, 5550 when the pattern 5551 5552 (foo)\Kbar 5553 5554 matches "foobar", the first substring is still set to "foo". 5555 5556 Perl documents that the use of \K within assertions is "not well 5557 defined". In PCRE, \K is acted upon when it occurs inside positive 5558 assertions, but is ignored in negative assertions. Note that when a 5559 pattern such as (?=ab\K) matches, the reported start of the match can 5560 be greater than the end of the match. 5561 5562 Simple assertions 5563 5564 The final use of backslash is for certain simple assertions. An asser- 5565 tion specifies a condition that has to be met at a particular point in 5566 a match, without consuming any characters from the subject string. The 5567 use of subpatterns for more complicated assertions is described below. 5568 The backslashed assertions are: 5569 5570 \b matches at a word boundary 5571 \B matches when not at a word boundary 5572 \A matches at the start of the subject 5573 \Z matches at the end of the subject 5574 also matches before a newline at the end of the subject 5575 \z matches only at the end of the subject 5576 \G matches at the first matching position in the subject 5577 5578 Inside a character class, \b has a different meaning; it matches the 5579 backspace character. If any other of these assertions appears in a 5580 character class, by default it matches the corresponding literal char- 5581 acter (for example, \B matches the letter B). However, if the 5582 PCRE_EXTRA option is set, an "invalid escape sequence" error is gener- 5583 ated instead. 5584 5585 A word boundary is a position in the subject string where the current 5586 character and the previous character do not both match \w or \W (i.e. 5587 one matches \w and the other matches \W), or the start or end of the 5588 string if the first or last character matches \w, respectively. In a 5589 UTF mode, the meanings of \w and \W can be changed by setting the 5590 PCRE_UCP option. When this is done, it also affects \b and \B. Neither 5591 PCRE nor Perl has a separate "start of word" or "end of word" metase- 5592 quence. However, whatever follows \b normally determines which it is. 5593 For example, the fragment \ba matches "a" at the start of a word. 5594 5595 The \A, \Z, and \z assertions differ from the traditional circumflex 5596 and dollar (described in the next section) in that they only ever match 5597 at the very start and end of the subject string, whatever options are 5598 set. Thus, they are independent of multiline mode. These three asser- 5599 tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which 5600 affect only the behaviour of the circumflex and dollar metacharacters. 5601 However, if the startoffset argument of pcre_exec() is non-zero, indi- 5602 cating that matching is to start at a point other than the beginning of 5603 the subject, \A can never match. The difference between \Z and \z is 5604 that \Z matches before a newline at the end of the string as well as at 5605 the very end, whereas \z matches only at the end. 5606 5607 The \G assertion is true only when the current matching position is at 5608 the start point of the match, as specified by the startoffset argument 5609 of pcre_exec(). It differs from \A when the value of startoffset is 5610 non-zero. By calling pcre_exec() multiple times with appropriate argu- 5611 ments, you can mimic Perl's /g option, and it is in this kind of imple- 5612 mentation where \G can be useful. 5613 5614 Note, however, that PCRE's interpretation of \G, as the start of the 5615 current match, is subtly different from Perl's, which defines it as the 5616 end of the previous match. In Perl, these can be different when the 5617 previously matched string was empty. Because PCRE does just one match 5618 at a time, it cannot reproduce this behaviour. 5619 5620 If all the alternatives of a pattern begin with \G, the expression is 5621 anchored to the starting match position, and the "anchored" flag is set 5622 in the compiled regular expression. 5623 5624 5625CIRCUMFLEX AND DOLLAR 5626 5627 The circumflex and dollar metacharacters are zero-width assertions. 5628 That is, they test for a particular condition being true without con- 5629 suming any characters from the subject string. 5630 5631 Outside a character class, in the default matching mode, the circumflex 5632 character is an assertion that is true only if the current matching 5633 point is at the start of the subject string. If the startoffset argu- 5634 ment of pcre_exec() is non-zero, circumflex can never match if the 5635 PCRE_MULTILINE option is unset. Inside a character class, circumflex 5636 has an entirely different meaning (see below). 5637 5638 Circumflex need not be the first character of the pattern if a number 5639 of alternatives are involved, but it should be the first thing in each 5640 alternative in which it appears if the pattern is ever to match that 5641 branch. If all possible alternatives start with a circumflex, that is, 5642 if the pattern is constrained to match only at the start of the sub- 5643 ject, it is said to be an "anchored" pattern. (There are also other 5644 constructs that can cause a pattern to be anchored.) 5645 5646 The dollar character is an assertion that is true only if the current 5647 matching point is at the end of the subject string, or immediately 5648 before a newline at the end of the string (by default). Note, however, 5649 that it does not actually match the newline. Dollar need not be the 5650 last character of the pattern if a number of alternatives are involved, 5651 but it should be the last item in any branch in which it appears. Dol- 5652 lar has no special meaning in a character class. 5653 5654 The meaning of dollar can be changed so that it matches only at the 5655 very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at 5656 compile time. This does not affect the \Z assertion. 5657 5658 The meanings of the circumflex and dollar characters are changed if the 5659 PCRE_MULTILINE option is set. When this is the case, a circumflex 5660 matches immediately after internal newlines as well as at the start of 5661 the subject string. It does not match after a newline that ends the 5662 string. A dollar matches before any newlines in the string, as well as 5663 at the very end, when PCRE_MULTILINE is set. When newline is specified 5664 as the two-character sequence CRLF, isolated CR and LF characters do 5665 not indicate newlines. 5666 5667 For example, the pattern /^abc$/ matches the subject string "def\nabc" 5668 (where \n represents a newline) in multiline mode, but not otherwise. 5669 Consequently, patterns that are anchored in single line mode because 5670 all branches start with ^ are not anchored in multiline mode, and a 5671 match for circumflex is possible when the startoffset argument of 5672 pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if 5673 PCRE_MULTILINE is set. 5674 5675 Note that the sequences \A, \Z, and \z can be used to match the start 5676 and end of the subject in both modes, and if all branches of a pattern 5677 start with \A it is always anchored, whether or not PCRE_MULTILINE is 5678 set. 5679 5680 5681FULL STOP (PERIOD, DOT) AND \N 5682 5683 Outside a character class, a dot in the pattern matches any one charac- 5684 ter in the subject string except (by default) a character that signi- 5685 fies the end of a line. 5686 5687 When a line ending is defined as a single character, dot never matches 5688 that character; when the two-character sequence CRLF is used, dot does 5689 not match CR if it is immediately followed by LF, but otherwise it 5690 matches all characters (including isolated CRs and LFs). When any Uni- 5691 code line endings are being recognized, dot does not match CR or LF or 5692 any of the other line ending characters. 5693 5694 The behaviour of dot with regard to newlines can be changed. If the 5695 PCRE_DOTALL option is set, a dot matches any one character, without 5696 exception. If the two-character sequence CRLF is present in the subject 5697 string, it takes two dots to match it. 5698 5699 The handling of dot is entirely independent of the handling of circum- 5700 flex and dollar, the only relationship being that they both involve 5701 newlines. Dot has no special meaning in a character class. 5702 5703 The escape sequence \N behaves like a dot, except that it is not 5704 affected by the PCRE_DOTALL option. In other words, it matches any 5705 character except one that signifies the end of a line. Perl also uses 5706 \N to match characters by name; PCRE does not support this. 5707 5708 5709MATCHING A SINGLE DATA UNIT 5710 5711 Outside a character class, the escape sequence \C matches any one data 5712 unit, whether or not a UTF mode is set. In the 8-bit library, one data 5713 unit is one byte; in the 16-bit library it is a 16-bit unit; in the 5714 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches 5715 line-ending characters. The feature is provided in Perl in order to 5716 match individual bytes in UTF-8 mode, but it is unclear how it can use- 5717 fully be used. Because \C breaks up characters into individual data 5718 units, matching one unit with \C in a UTF mode means that the rest of 5719 the string may start with a malformed UTF character. This has undefined 5720 results, because PCRE assumes that it is dealing with valid UTF strings 5721 (and by default it checks this at the start of processing unless the 5722 PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option 5723 is used). 5724 5725 PCRE does not allow \C to appear in lookbehind assertions (described 5726 below) in a UTF mode, because this would make it impossible to calcu- 5727 late the length of the lookbehind. 5728 5729 In general, the \C escape sequence is best avoided. However, one way of 5730 using it that avoids the problem of malformed UTF characters is to use 5731 a lookahead to check the length of the next character, as in this pat- 5732 tern, which could be used with a UTF-8 string (ignore white space and 5733 line breaks): 5734 5735 (?| (?=[\x00-\x7f])(\C) | 5736 (?=[\x80-\x{7ff}])(\C)(\C) | 5737 (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) | 5738 (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C)) 5739 5740 A group that starts with (?| resets the capturing parentheses numbers 5741 in each alternative (see "Duplicate Subpattern Numbers" below). The 5742 assertions at the start of each branch check the next UTF-8 character 5743 for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The 5744 character's individual bytes are then captured by the appropriate num- 5745 ber of groups. 5746 5747 5748SQUARE BRACKETS AND CHARACTER CLASSES 5749 5750 An opening square bracket introduces a character class, terminated by a 5751 closing square bracket. A closing square bracket on its own is not spe- 5752 cial by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set, 5753 a lone closing square bracket causes a compile-time error. If a closing 5754 square bracket is required as a member of the class, it should be the 5755 first data character in the class (after an initial circumflex, if 5756 present) or escaped with a backslash. 5757 5758 A character class matches a single character in the subject. In a UTF 5759 mode, the character may be more than one data unit long. A matched 5760 character must be in the set of characters defined by the class, unless 5761 the first character in the class definition is a circumflex, in which 5762 case the subject character must not be in the set defined by the class. 5763 If a circumflex is actually required as a member of the class, ensure 5764 it is not the first character, or escape it with a backslash. 5765 5766 For example, the character class [aeiou] matches any lower case vowel, 5767 while [^aeiou] matches any character that is not a lower case vowel. 5768 Note that a circumflex is just a convenient notation for specifying the 5769 characters that are in the class by enumerating those that are not. A 5770 class that starts with a circumflex is not an assertion; it still con- 5771 sumes a character from the subject string, and therefore it fails if 5772 the current pointer is at the end of the string. 5773 5774 In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255 5775 (0xffff) can be included in a class as a literal string of data units, 5776 or by using the \x{ escaping mechanism. 5777 5778 When caseless matching is set, any letters in a class represent both 5779 their upper case and lower case versions, so for example, a caseless 5780 [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not 5781 match "A", whereas a caseful version would. In a UTF mode, PCRE always 5782 understands the concept of case for characters whose values are less 5783 than 128, so caseless matching is always possible. For characters with 5784 higher values, the concept of case is supported if PCRE is compiled 5785 with Unicode property support, but not otherwise. If you want to use 5786 caseless matching in a UTF mode for characters 128 and above, you must 5787 ensure that PCRE is compiled with Unicode property support as well as 5788 with UTF support. 5789 5790 Characters that might indicate line breaks are never treated in any 5791 special way when matching character classes, whatever line-ending 5792 sequence is in use, and whatever setting of the PCRE_DOTALL and 5793 PCRE_MULTILINE options is used. A class such as [^a] always matches one 5794 of these characters. 5795 5796 The minus (hyphen) character can be used to specify a range of charac- 5797 ters in a character class. For example, [d-m] matches any letter 5798 between d and m, inclusive. If a minus character is required in a 5799 class, it must be escaped with a backslash or appear in a position 5800 where it cannot be interpreted as indicating a range, typically as the 5801 first or last character in the class, or immediately after a range. For 5802 example, [b-d-z] matches letters in the range b to d, a hyphen charac- 5803 ter, or z. 5804 5805 It is not possible to have the literal character "]" as the end charac- 5806 ter of a range. A pattern such as [W-]46] is interpreted as a class of 5807 two characters ("W" and "-") followed by a literal string "46]", so it 5808 would match "W46]" or "-46]". However, if the "]" is escaped with a 5809 backslash it is interpreted as the end of range, so [W-\]46] is inter- 5810 preted as a class containing a range followed by two other characters. 5811 The octal or hexadecimal representation of "]" can also be used to end 5812 a range. 5813 5814 An error is generated if a POSIX character class (see below) or an 5815 escape sequence other than one that defines a single character appears 5816 at a point where a range ending character is expected. For example, 5817 [z-\xff] is valid, but [A-\d] and [A-[:digit:]] are not. 5818 5819 Ranges operate in the collating sequence of character values. They can 5820 also be used for characters specified numerically, for example 5821 [\000-\037]. Ranges can include any characters that are valid for the 5822 current mode. 5823 5824 If a range that includes letters is used when caseless matching is set, 5825 it matches the letters in either case. For example, [W-c] is equivalent 5826 to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if 5827 character tables for a French locale are in use, [\xc8-\xcb] matches 5828 accented E characters in both cases. In UTF modes, PCRE supports the 5829 concept of case for characters with values greater than 128 only when 5830 it is compiled with Unicode property support. 5831 5832 The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, 5833 \w, and \W may appear in a character class, and add the characters that 5834 they match to the class. For example, [\dABCDEF] matches any hexadeci- 5835 mal digit. In UTF modes, the PCRE_UCP option affects the meanings of 5836 \d, \s, \w and their upper case partners, just as it does when they 5837 appear outside a character class, as described in the section entitled 5838 "Generic character types" above. The escape sequence \b has a different 5839 meaning inside a character class; it matches the backspace character. 5840 The sequences \B, \N, \R, and \X are not special inside a character 5841 class. Like any other unrecognized escape sequences, they are treated 5842 as the literal characters "B", "N", "R", and "X" by default, but cause 5843 an error if the PCRE_EXTRA option is set. 5844 5845 A circumflex can conveniently be used with the upper case character 5846 types to specify a more restricted set of characters than the matching 5847 lower case type. For example, the class [^\W_] matches any letter or 5848 digit, but not underscore, whereas [\w] includes underscore. A positive 5849 character class should be read as "something OR something OR ..." and a 5850 negative class as "NOT something AND NOT something AND NOT ...". 5851 5852 The only metacharacters that are recognized in character classes are 5853 backslash, hyphen (only where it can be interpreted as specifying a 5854 range), circumflex (only at the start), opening square bracket (only 5855 when it can be interpreted as introducing a POSIX class name, or for a 5856 special compatibility feature - see the next two sections), and the 5857 terminating closing square bracket. However, escaping other non- 5858 alphanumeric characters does no harm. 5859 5860 5861POSIX CHARACTER CLASSES 5862 5863 Perl supports the POSIX notation for character classes. This uses names 5864 enclosed by [: and :] within the enclosing square brackets. PCRE also 5865 supports this notation. For example, 5866 5867 [01[:alpha:]%] 5868 5869 matches "0", "1", any alphabetic character, or "%". The supported class 5870 names are: 5871 5872 alnum letters and digits 5873 alpha letters 5874 ascii character codes 0 - 127 5875 blank space or tab only 5876 cntrl control characters 5877 digit decimal digits (same as \d) 5878 graph printing characters, excluding space 5879 lower lower case letters 5880 print printing characters, including space 5881 punct printing characters, excluding letters and digits and space 5882 space white space (the same as \s from PCRE 8.34) 5883 upper upper case letters 5884 word "word" characters (same as \w) 5885 xdigit hexadecimal digits 5886 5887 The default "space" characters are HT (9), LF (10), VT (11), FF (12), 5888 CR (13), and space (32). If locale-specific matching is taking place, 5889 the list of space characters may be different; there may be fewer or 5890 more of them. "Space" used to be different to \s, which did not include 5891 VT, for Perl compatibility. However, Perl changed at release 5.18, and 5892 PCRE followed at release 8.34. "Space" and \s now match the same set 5893 of characters. 5894 5895 The name "word" is a Perl extension, and "blank" is a GNU extension 5896 from Perl 5.8. Another Perl extension is negation, which is indicated 5897 by a ^ character after the colon. For example, 5898 5899 [12[:^digit:]] 5900 5901 matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the 5902 POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but 5903 these are not supported, and an error is given if they are encountered. 5904 5905 By default, characters with values greater than 128 do not match any of 5906 the POSIX character classes. However, if the PCRE_UCP option is passed 5907 to pcre_compile(), some of the classes are changed so that Unicode 5908 character properties are used. This is achieved by replacing certain 5909 POSIX classes by other sequences, as follows: 5910 5911 [:alnum:] becomes \p{Xan} 5912 [:alpha:] becomes \p{L} 5913 [:blank:] becomes \h 5914 [:digit:] becomes \p{Nd} 5915 [:lower:] becomes \p{Ll} 5916 [:space:] becomes \p{Xps} 5917 [:upper:] becomes \p{Lu} 5918 [:word:] becomes \p{Xwd} 5919 5920 Negated versions, such as [:^alpha:] use \P instead of \p. Three other 5921 POSIX classes are handled specially in UCP mode: 5922 5923 [:graph:] This matches characters that have glyphs that mark the page 5924 when printed. In Unicode property terms, it matches all char- 5925 acters with the L, M, N, P, S, or Cf properties, except for: 5926 5927 U+061C Arabic Letter Mark 5928 U+180E Mongolian Vowel Separator 5929 U+2066 - U+2069 Various "isolate"s 5930 5931 5932 [:print:] This matches the same characters as [:graph:] plus space 5933 characters that are not controls, that is, characters with 5934 the Zs property. 5935 5936 [:punct:] This matches all characters that have the Unicode P (punctua- 5937 tion) property, plus those characters whose code points are 5938 less than 128 that have the S (Symbol) property. 5939 5940 The other POSIX classes are unchanged, and match only characters with 5941 code points less than 128. 5942 5943 5944COMPATIBILITY FEATURE FOR WORD BOUNDARIES 5945 5946 In the POSIX.2 compliant library that was included in 4.4BSD Unix, the 5947 ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word" 5948 and "end of word". PCRE treats these items as follows: 5949 5950 [[:<:]] is converted to \b(?=\w) 5951 [[:>:]] is converted to \b(?<=\w) 5952 5953 Only these exact character sequences are recognized. A sequence such as 5954 [a[:<:]b] provokes error for an unrecognized POSIX class name. This 5955 support is not compatible with Perl. It is provided to help migrations 5956 from other environments, and is best not used in any new patterns. Note 5957 that \b matches at the start and the end of a word (see "Simple asser- 5958 tions" above), and in a Perl-style pattern the preceding or following 5959 character normally shows which is wanted, without the need for the 5960 assertions that are used above in order to give exactly the POSIX be- 5961 haviour. 5962 5963 5964VERTICAL BAR 5965 5966 Vertical bar characters are used to separate alternative patterns. For 5967 example, the pattern 5968 5969 gilbert|sullivan 5970 5971 matches either "gilbert" or "sullivan". Any number of alternatives may 5972 appear, and an empty alternative is permitted (matching the empty 5973 string). The matching process tries each alternative in turn, from left 5974 to right, and the first one that succeeds is used. If the alternatives 5975 are within a subpattern (defined below), "succeeds" means matching the 5976 rest of the main pattern as well as the alternative in the subpattern. 5977 5978 5979INTERNAL OPTION SETTING 5980 5981 The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and 5982 PCRE_EXTENDED options (which are Perl-compatible) can be changed from 5983 within the pattern by a sequence of Perl option letters enclosed 5984 between "(?" and ")". The option letters are 5985 5986 i for PCRE_CASELESS 5987 m for PCRE_MULTILINE 5988 s for PCRE_DOTALL 5989 x for PCRE_EXTENDED 5990 5991 For example, (?im) sets caseless, multiline matching. It is also possi- 5992 ble to unset these options by preceding the letter with a hyphen, and a 5993 combined setting and unsetting such as (?im-sx), which sets PCRE_CASE- 5994 LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, 5995 is also permitted. If a letter appears both before and after the 5996 hyphen, the option is unset. 5997 5998 The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA 5999 can be changed in the same way as the Perl-compatible options by using 6000 the characters J, U and X respectively. 6001 6002 When one of these option changes occurs at top level (that is, not 6003 inside subpattern parentheses), the change applies to the remainder of 6004 the pattern that follows. An option change within a subpattern (see 6005 below for a description of subpatterns) affects only that part of the 6006 subpattern that follows it, so 6007 6008 (a(?i)b)c 6009 6010 matches abc and aBc and no other strings (assuming PCRE_CASELESS is not 6011 used). By this means, options can be made to have different settings 6012 in different parts of the pattern. Any changes made in one alternative 6013 do carry on into subsequent branches within the same subpattern. For 6014 example, 6015 6016 (a(?i)b|c) 6017 6018 matches "ab", "aB", "c", and "C", even though when matching "C" the 6019 first branch is abandoned before the option setting. This is because 6020 the effects of option settings happen at compile time. There would be 6021 some very weird behaviour otherwise. 6022 6023 Note: There are other PCRE-specific options that can be set by the 6024 application when the compiling or matching functions are called. In 6025 some cases the pattern can contain special leading sequences such as 6026 (*CRLF) to override what the application has set or what has been 6027 defaulted. Details are given in the section entitled "Newline 6028 sequences" above. There are also the (*UTF8), (*UTF16),(*UTF32), and 6029 (*UCP) leading sequences that can be used to set UTF and Unicode prop- 6030 erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, 6031 PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence 6032 is a generic version that can be used with any of the libraries. How- 6033 ever, the application can set the PCRE_NEVER_UTF option, which locks 6034 out the use of the (*UTF) sequences. 6035 6036 6037SUBPATTERNS 6038 6039 Subpatterns are delimited by parentheses (round brackets), which can be 6040 nested. Turning part of a pattern into a subpattern does two things: 6041 6042 1. It localizes a set of alternatives. For example, the pattern 6043 6044 cat(aract|erpillar|) 6045 6046 matches "cataract", "caterpillar", or "cat". Without the parentheses, 6047 it would match "cataract", "erpillar" or an empty string. 6048 6049 2. It sets up the subpattern as a capturing subpattern. This means 6050 that, when the whole pattern matches, that portion of the subject 6051 string that matched the subpattern is passed back to the caller via the 6052 ovector argument of the matching function. (This applies only to the 6053 traditional matching functions; the DFA matching functions do not sup- 6054 port capturing.) 6055 6056 Opening parentheses are counted from left to right (starting from 1) to 6057 obtain numbers for the capturing subpatterns. For example, if the 6058 string "the red king" is matched against the pattern 6059 6060 the ((red|white) (king|queen)) 6061 6062 the captured substrings are "red king", "red", and "king", and are num- 6063 bered 1, 2, and 3, respectively. 6064 6065 The fact that plain parentheses fulfil two functions is not always 6066 helpful. There are often times when a grouping subpattern is required 6067 without a capturing requirement. If an opening parenthesis is followed 6068 by a question mark and a colon, the subpattern does not do any captur- 6069 ing, and is not counted when computing the number of any subsequent 6070 capturing subpatterns. For example, if the string "the white queen" is 6071 matched against the pattern 6072 6073 the ((?:red|white) (king|queen)) 6074 6075 the captured substrings are "white queen" and "queen", and are numbered 6076 1 and 2. The maximum number of capturing subpatterns is 65535. 6077 6078 As a convenient shorthand, if any option settings are required at the 6079 start of a non-capturing subpattern, the option letters may appear 6080 between the "?" and the ":". Thus the two patterns 6081 6082 (?i:saturday|sunday) 6083 (?:(?i)saturday|sunday) 6084 6085 match exactly the same set of strings. Because alternative branches are 6086 tried from left to right, and options are not reset until the end of 6087 the subpattern is reached, an option setting in one branch does affect 6088 subsequent branches, so the above patterns match "SUNDAY" as well as 6089 "Saturday". 6090 6091 6092DUPLICATE SUBPATTERN NUMBERS 6093 6094 Perl 5.10 introduced a feature whereby each alternative in a subpattern 6095 uses the same numbers for its capturing parentheses. Such a subpattern 6096 starts with (?| and is itself a non-capturing subpattern. For example, 6097 consider this pattern: 6098 6099 (?|(Sat)ur|(Sun))day 6100 6101 Because the two alternatives are inside a (?| group, both sets of cap- 6102 turing parentheses are numbered one. Thus, when the pattern matches, 6103 you can look at captured substring number one, whichever alternative 6104 matched. This construct is useful when you want to capture part, but 6105 not all, of one of a number of alternatives. Inside a (?| group, paren- 6106 theses are numbered as usual, but the number is reset at the start of 6107 each branch. The numbers of any capturing parentheses that follow the 6108 subpattern start after the highest number used in any branch. The fol- 6109 lowing example is taken from the Perl documentation. The numbers under- 6110 neath show in which buffer the captured content will be stored. 6111 6112 # before ---------------branch-reset----------- after 6113 / ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x 6114 # 1 2 2 3 2 3 4 6115 6116 A back reference to a numbered subpattern uses the most recent value 6117 that is set for that number by any subpattern. The following pattern 6118 matches "abcabc" or "defdef": 6119 6120 /(?|(abc)|(def))\1/ 6121 6122 In contrast, a subroutine call to a numbered subpattern always refers 6123 to the first one in the pattern with the given number. The following 6124 pattern matches "abcabc" or "defabc": 6125 6126 /(?|(abc)|(def))(?1)/ 6127 6128 If a condition test for a subpattern's having matched refers to a non- 6129 unique number, the test is true if any of the subpatterns of that num- 6130 ber have matched. 6131 6132 An alternative approach to using this "branch reset" feature is to use 6133 duplicate named subpatterns, as described in the next section. 6134 6135 6136NAMED SUBPATTERNS 6137 6138 Identifying capturing parentheses by number is simple, but it can be 6139 very hard to keep track of the numbers in complicated regular expres- 6140 sions. Furthermore, if an expression is modified, the numbers may 6141 change. To help with this difficulty, PCRE supports the naming of sub- 6142 patterns. This feature was not added to Perl until release 5.10. Python 6143 had the feature earlier, and PCRE introduced it at release 4.0, using 6144 the Python syntax. PCRE now supports both the Perl and the Python syn- 6145 tax. Perl allows identically numbered subpatterns to have different 6146 names, but PCRE does not. 6147 6148 In PCRE, a subpattern can be named in one of three ways: (?<name>...) 6149 or (?'name'...) as in Perl, or (?P<name>...) as in Python. References 6150 to capturing parentheses from other parts of the pattern, such as back 6151 references, recursion, and conditions, can be made by name as well as 6152 by number. 6153 6154 Names consist of up to 32 alphanumeric characters and underscores, but 6155 must start with a non-digit. Named capturing parentheses are still 6156 allocated numbers as well as names, exactly as if the names were not 6157 present. The PCRE API provides function calls for extracting the name- 6158 to-number translation table from a compiled pattern. There is also a 6159 convenience function for extracting a captured substring by name. 6160 6161 By default, a name must be unique within a pattern, but it is possible 6162 to relax this constraint by setting the PCRE_DUPNAMES option at compile 6163 time. (Duplicate names are also always permitted for subpatterns with 6164 the same number, set up as described in the previous section.) Dupli- 6165 cate names can be useful for patterns where only one instance of the 6166 named parentheses can match. Suppose you want to match the name of a 6167 weekday, either as a 3-letter abbreviation or as the full name, and in 6168 both cases you want to extract the abbreviation. This pattern (ignoring 6169 the line breaks) does the job: 6170 6171 (?<DN>Mon|Fri|Sun)(?:day)?| 6172 (?<DN>Tue)(?:sday)?| 6173 (?<DN>Wed)(?:nesday)?| 6174 (?<DN>Thu)(?:rsday)?| 6175 (?<DN>Sat)(?:urday)? 6176 6177 There are five capturing substrings, but only one is ever set after a 6178 match. (An alternative way of solving this problem is to use a "branch 6179 reset" subpattern, as described in the previous section.) 6180 6181 The convenience function for extracting the data by name returns the 6182 substring for the first (and in this example, the only) subpattern of 6183 that name that matched. This saves searching to find which numbered 6184 subpattern it was. 6185 6186 If you make a back reference to a non-unique named subpattern from 6187 elsewhere in the pattern, the subpatterns to which the name refers are 6188 checked in the order in which they appear in the overall pattern. The 6189 first one that is set is used for the reference. For example, this pat- 6190 tern matches both "foofoo" and "barbar" but not "foobar" or "barfoo": 6191 6192 (?:(?<n>foo)|(?<n>bar))\k<n> 6193 6194 6195 If you make a subroutine call to a non-unique named subpattern, the one 6196 that corresponds to the first occurrence of the name is used. In the 6197 absence of duplicate numbers (see the previous section) this is the one 6198 with the lowest number. 6199 6200 If you use a named reference in a condition test (see the section about 6201 conditions below), either to check whether a subpattern has matched, or 6202 to check for recursion, all subpatterns with the same name are tested. 6203 If the condition is true for any one of them, the overall condition is 6204 true. This is the same behaviour as testing by number. For further 6205 details of the interfaces for handling named subpatterns, see the 6206 pcreapi documentation. 6207 6208 Warning: You cannot use different names to distinguish between two sub- 6209 patterns with the same number because PCRE uses only the numbers when 6210 matching. For this reason, an error is given at compile time if differ- 6211 ent names are given to subpatterns with the same number. However, you 6212 can always give the same name to subpatterns with the same number, even 6213 when PCRE_DUPNAMES is not set. 6214 6215 6216REPETITION 6217 6218 Repetition is specified by quantifiers, which can follow any of the 6219 following items: 6220 6221 a literal data character 6222 the dot metacharacter 6223 the \C escape sequence 6224 the \X escape sequence 6225 the \R escape sequence 6226 an escape such as \d or \pL that matches a single character 6227 a character class 6228 a back reference (see next section) 6229 a parenthesized subpattern (including assertions) 6230 a subroutine call to a subpattern (recursive or otherwise) 6231 6232 The general repetition quantifier specifies a minimum and maximum num- 6233 ber of permitted matches, by giving the two numbers in curly brackets 6234 (braces), separated by a comma. The numbers must be less than 65536, 6235 and the first must be less than or equal to the second. For example: 6236 6237 z{2,4} 6238 6239 matches "zz", "zzz", or "zzzz". A closing brace on its own is not a 6240 special character. If the second number is omitted, but the comma is 6241 present, there is no upper limit; if the second number and the comma 6242 are both omitted, the quantifier specifies an exact number of required 6243 matches. Thus 6244 6245 [aeiou]{3,} 6246 6247 matches at least 3 successive vowels, but may match many more, while 6248 6249 \d{8} 6250 6251 matches exactly 8 digits. An opening curly bracket that appears in a 6252 position where a quantifier is not allowed, or one that does not match 6253 the syntax of a quantifier, is taken as a literal character. For exam- 6254 ple, {,6} is not a quantifier, but a literal string of four characters. 6255 6256 In UTF modes, quantifiers apply to characters rather than to individual 6257 data units. Thus, for example, \x{100}{2} matches two characters, each 6258 of which is represented by a two-byte sequence in a UTF-8 string. Simi- 6259 larly, \X{3} matches three Unicode extended grapheme clusters, each of 6260 which may be several data units long (and they may be of different 6261 lengths). 6262 6263 The quantifier {0} is permitted, causing the expression to behave as if 6264 the previous item and the quantifier were not present. This may be use- 6265 ful for subpatterns that are referenced as subroutines from elsewhere 6266 in the pattern (but see also the section entitled "Defining subpatterns 6267 for use by reference only" below). Items other than subpatterns that 6268 have a {0} quantifier are omitted from the compiled pattern. 6269 6270 For convenience, the three most common quantifiers have single-charac- 6271 ter abbreviations: 6272 6273 * is equivalent to {0,} 6274 + is equivalent to {1,} 6275 ? is equivalent to {0,1} 6276 6277 It is possible to construct infinite loops by following a subpattern 6278 that can match no characters with a quantifier that has no upper limit, 6279 for example: 6280 6281 (a?)* 6282 6283 Earlier versions of Perl and PCRE used to give an error at compile time 6284 for such patterns. However, because there are cases where this can be 6285 useful, such patterns are now accepted, but if any repetition of the 6286 subpattern does in fact match no characters, the loop is forcibly bro- 6287 ken. 6288 6289 By default, the quantifiers are "greedy", that is, they match as much 6290 as possible (up to the maximum number of permitted times), without 6291 causing the rest of the pattern to fail. The classic example of where 6292 this gives problems is in trying to match comments in C programs. These 6293 appear between /* and */ and within the comment, individual * and / 6294 characters may appear. An attempt to match C comments by applying the 6295 pattern 6296 6297 /\*.*\*/ 6298 6299 to the string 6300 6301 /* first comment */ not comment /* second comment */ 6302 6303 fails, because it matches the entire string owing to the greediness of 6304 the .* item. 6305 6306 However, if a quantifier is followed by a question mark, it ceases to 6307 be greedy, and instead matches the minimum number of times possible, so 6308 the pattern 6309 6310 /\*.*?\*/ 6311 6312 does the right thing with the C comments. The meaning of the various 6313 quantifiers is not otherwise changed, just the preferred number of 6314 matches. Do not confuse this use of question mark with its use as a 6315 quantifier in its own right. Because it has two uses, it can sometimes 6316 appear doubled, as in 6317 6318 \d??\d 6319 6320 which matches one digit by preference, but can match two if that is the 6321 only way the rest of the pattern matches. 6322 6323 If the PCRE_UNGREEDY option is set (an option that is not available in 6324 Perl), the quantifiers are not greedy by default, but individual ones 6325 can be made greedy by following them with a question mark. In other 6326 words, it inverts the default behaviour. 6327 6328 When a parenthesized subpattern is quantified with a minimum repeat 6329 count that is greater than 1 or with a limited maximum, more memory is 6330 required for the compiled pattern, in proportion to the size of the 6331 minimum or maximum. 6332 6333 If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv- 6334 alent to Perl's /s) is set, thus allowing the dot to match newlines, 6335 the pattern is implicitly anchored, because whatever follows will be 6336 tried against every character position in the subject string, so there 6337 is no point in retrying the overall match at any position after the 6338 first. PCRE normally treats such a pattern as though it were preceded 6339 by \A. 6340 6341 In cases where it is known that the subject string contains no new- 6342 lines, it is worth setting PCRE_DOTALL in order to obtain this opti- 6343 mization, or alternatively using ^ to indicate anchoring explicitly. 6344 6345 However, there are some cases where the optimization cannot be used. 6346 When .* is inside capturing parentheses that are the subject of a back 6347 reference elsewhere in the pattern, a match at the start may fail where 6348 a later one succeeds. Consider, for example: 6349 6350 (.*)abc\1 6351 6352 If the subject is "xyz123abc123" the match point is the fourth charac- 6353 ter. For this reason, such a pattern is not implicitly anchored. 6354 6355 Another case where implicit anchoring is not applied is when the lead- 6356 ing .* is inside an atomic group. Once again, a match at the start may 6357 fail where a later one succeeds. Consider this pattern: 6358 6359 (?>.*?a)b 6360 6361 It matches "ab" in the subject "aab". The use of the backtracking con- 6362 trol verbs (*PRUNE) and (*SKIP) also disable this optimization. 6363 6364 When a capturing subpattern is repeated, the value captured is the sub- 6365 string that matched the final iteration. For example, after 6366 6367 (tweedle[dume]{3}\s*)+ 6368 6369 has matched "tweedledum tweedledee" the value of the captured substring 6370 is "tweedledee". However, if there are nested capturing subpatterns, 6371 the corresponding captured values may have been set in previous itera- 6372 tions. For example, after 6373 6374 /(a|(b))+/ 6375 6376 matches "aba" the value of the second captured substring is "b". 6377 6378 6379ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS 6380 6381 With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") 6382 repetition, failure of what follows normally causes the repeated item 6383 to be re-evaluated to see if a different number of repeats allows the 6384 rest of the pattern to match. Sometimes it is useful to prevent this, 6385 either to change the nature of the match, or to cause it fail earlier 6386 than it otherwise might, when the author of the pattern knows there is 6387 no point in carrying on. 6388 6389 Consider, for example, the pattern \d+foo when applied to the subject 6390 line 6391 6392 123456bar 6393 6394 After matching all 6 digits and then failing to match "foo", the normal 6395 action of the matcher is to try again with only 5 digits matching the 6396 \d+ item, and then with 4, and so on, before ultimately failing. 6397 "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides 6398 the means for specifying that once a subpattern has matched, it is not 6399 to be re-evaluated in this way. 6400 6401 If we use atomic grouping for the previous example, the matcher gives 6402 up immediately on failing to match "foo" the first time. The notation 6403 is a kind of special parenthesis, starting with (?> as in this example: 6404 6405 (?>\d+)foo 6406 6407 This kind of parenthesis "locks up" the part of the pattern it con- 6408 tains once it has matched, and a failure further into the pattern is 6409 prevented from backtracking into it. Backtracking past it to previous 6410 items, however, works as normal. 6411 6412 An alternative description is that a subpattern of this type matches 6413 the string of characters that an identical standalone pattern would 6414 match, if anchored at the current point in the subject string. 6415 6416 Atomic grouping subpatterns are not capturing subpatterns. Simple cases 6417 such as the above example can be thought of as a maximizing repeat that 6418 must swallow everything it can. So, while both \d+ and \d+? are pre- 6419 pared to adjust the number of digits they match in order to make the 6420 rest of the pattern match, (?>\d+) can only match an entire sequence of 6421 digits. 6422 6423 Atomic groups in general can of course contain arbitrarily complicated 6424 subpatterns, and can be nested. However, when the subpattern for an 6425 atomic group is just a single repeated item, as in the example above, a 6426 simpler notation, called a "possessive quantifier" can be used. This 6427 consists of an additional + character following a quantifier. Using 6428 this notation, the previous example can be rewritten as 6429 6430 \d++foo 6431 6432 Note that a possessive quantifier can be used with an entire group, for 6433 example: 6434 6435 (abc|xyz){2,3}+ 6436 6437 Possessive quantifiers are always greedy; the setting of the 6438 PCRE_UNGREEDY option is ignored. They are a convenient notation for the 6439 simpler forms of atomic group. However, there is no difference in the 6440 meaning of a possessive quantifier and the equivalent atomic group, 6441 though there may be a performance difference; possessive quantifiers 6442 should be slightly faster. 6443 6444 The possessive quantifier syntax is an extension to the Perl 5.8 syn- 6445 tax. Jeffrey Friedl originated the idea (and the name) in the first 6446 edition of his book. Mike McCloskey liked it, so implemented it when he 6447 built Sun's Java package, and PCRE copied it from there. It ultimately 6448 found its way into Perl at release 5.10. 6449 6450 PCRE has an optimization that automatically "possessifies" certain sim- 6451 ple pattern constructs. For example, the sequence A+B is treated as 6452 A++B because there is no point in backtracking into a sequence of A's 6453 when B must follow. 6454 6455 When a pattern contains an unlimited repeat inside a subpattern that 6456 can itself be repeated an unlimited number of times, the use of an 6457 atomic group is the only way to avoid some failing matches taking a 6458 very long time indeed. The pattern 6459 6460 (\D+|<\d+>)*[!?] 6461 6462 matches an unlimited number of substrings that either consist of non- 6463 digits, or digits enclosed in <>, followed by either ! or ?. When it 6464 matches, it runs quickly. However, if it is applied to 6465 6466 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 6467 6468 it takes a long time before reporting failure. This is because the 6469 string can be divided between the internal \D+ repeat and the external 6470 * repeat in a large number of ways, and all have to be tried. (The 6471 example uses [!?] rather than a single character at the end, because 6472 both PCRE and Perl have an optimization that allows for fast failure 6473 when a single character is used. They remember the last single charac- 6474 ter that is required for a match, and fail early if it is not present 6475 in the string.) If the pattern is changed so that it uses an atomic 6476 group, like this: 6477 6478 ((?>\D+)|<\d+>)*[!?] 6479 6480 sequences of non-digits cannot be broken, and failure happens quickly. 6481 6482 6483BACK REFERENCES 6484 6485 Outside a character class, a backslash followed by a digit greater than 6486 0 (and possibly further digits) is a back reference to a capturing sub- 6487 pattern earlier (that is, to its left) in the pattern, provided there 6488 have been that many previous capturing left parentheses. 6489 6490 However, if the decimal number following the backslash is less than 10, 6491 it is always taken as a back reference, and causes an error only if 6492 there are not that many capturing left parentheses in the entire pat- 6493 tern. In other words, the parentheses that are referenced need not be 6494 to the left of the reference for numbers less than 10. A "forward back 6495 reference" of this type can make sense when a repetition is involved 6496 and the subpattern to the right has participated in an earlier itera- 6497 tion. 6498 6499 It is not possible to have a numerical "forward back reference" to a 6500 subpattern whose number is 10 or more using this syntax because a 6501 sequence such as \50 is interpreted as a character defined in octal. 6502 See the subsection entitled "Non-printing characters" above for further 6503 details of the handling of digits following a backslash. There is no 6504 such problem when named parentheses are used. A back reference to any 6505 subpattern is possible using named parentheses (see below). 6506 6507 Another way of avoiding the ambiguity inherent in the use of digits 6508 following a backslash is to use the \g escape sequence. This escape 6509 must be followed by an unsigned number or a negative number, optionally 6510 enclosed in braces. These examples are all identical: 6511 6512 (ring), \1 6513 (ring), \g1 6514 (ring), \g{1} 6515 6516 An unsigned number specifies an absolute reference without the ambigu- 6517 ity that is present in the older syntax. It is also useful when literal 6518 digits follow the reference. A negative number is a relative reference. 6519 Consider this example: 6520 6521 (abc(def)ghi)\g{-1} 6522 6523 The sequence \g{-1} is a reference to the most recently started captur- 6524 ing subpattern before \g, that is, is it equivalent to \2 in this exam- 6525 ple. Similarly, \g{-2} would be equivalent to \1. The use of relative 6526 references can be helpful in long patterns, and also in patterns that 6527 are created by joining together fragments that contain references 6528 within themselves. 6529 6530 A back reference matches whatever actually matched the capturing sub- 6531 pattern in the current subject string, rather than anything matching 6532 the subpattern itself (see "Subpatterns as subroutines" below for a way 6533 of doing that). So the pattern 6534 6535 (sens|respons)e and \1ibility 6536 6537 matches "sense and sensibility" and "response and responsibility", but 6538 not "sense and responsibility". If caseful matching is in force at the 6539 time of the back reference, the case of letters is relevant. For exam- 6540 ple, 6541 6542 ((?i)rah)\s+\1 6543 6544 matches "rah rah" and "RAH RAH", but not "RAH rah", even though the 6545 original capturing subpattern is matched caselessly. 6546 6547 There are several different ways of writing back references to named 6548 subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or 6549 \k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's 6550 unified back reference syntax, in which \g can be used for both numeric 6551 and named references, is also supported. We could rewrite the above 6552 example in any of the following ways: 6553 6554 (?<p1>(?i)rah)\s+\k<p1> 6555 (?'p1'(?i)rah)\s+\k{p1} 6556 (?P<p1>(?i)rah)\s+(?P=p1) 6557 (?<p1>(?i)rah)\s+\g{p1} 6558 6559 A subpattern that is referenced by name may appear in the pattern 6560 before or after the reference. 6561 6562 There may be more than one back reference to the same subpattern. If a 6563 subpattern has not actually been used in a particular match, any back 6564 references to it always fail by default. For example, the pattern 6565 6566 (a|(bc))\2 6567 6568 always fails if it starts to match "a" rather than "bc". However, if 6569 the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer- 6570 ence to an unset value matches an empty string. 6571 6572 Because there may be many capturing parentheses in a pattern, all dig- 6573 its following a backslash are taken as part of a potential back refer- 6574 ence number. If the pattern continues with a digit character, some 6575 delimiter must be used to terminate the back reference. If the 6576 PCRE_EXTENDED option is set, this can be white space. Otherwise, the 6577 \g{ syntax or an empty comment (see "Comments" below) can be used. 6578 6579 Recursive back references 6580 6581 A back reference that occurs inside the parentheses to which it refers 6582 fails when the subpattern is first used, so, for example, (a\1) never 6583 matches. However, such references can be useful inside repeated sub- 6584 patterns. For example, the pattern 6585 6586 (a|b\1)+ 6587 6588 matches any number of "a"s and also "aba", "ababbaa" etc. At each iter- 6589 ation of the subpattern, the back reference matches the character 6590 string corresponding to the previous iteration. In order for this to 6591 work, the pattern must be such that the first iteration does not need 6592 to match the back reference. This can be done using alternation, as in 6593 the example above, or by a quantifier with a minimum of zero. 6594 6595 Back references of this type cause the group that they reference to be 6596 treated as an atomic group. Once the whole group has been matched, a 6597 subsequent matching failure cannot cause backtracking into the middle 6598 of the group. 6599 6600 6601ASSERTIONS 6602 6603 An assertion is a test on the characters following or preceding the 6604 current matching point that does not actually consume any characters. 6605 The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are 6606 described above. 6607 6608 More complicated assertions are coded as subpatterns. There are two 6609 kinds: those that look ahead of the current position in the subject 6610 string, and those that look behind it. An assertion subpattern is 6611 matched in the normal way, except that it does not cause the current 6612 matching position to be changed. 6613 6614 Assertion subpatterns are not capturing subpatterns. If such an asser- 6615 tion contains capturing subpatterns within it, these are counted for 6616 the purposes of numbering the capturing subpatterns in the whole pat- 6617 tern. However, substring capturing is carried out only for positive 6618 assertions. (Perl sometimes, but not always, does do capturing in nega- 6619 tive assertions.) 6620 6621 WARNING: If a positive assertion containing one or more capturing sub- 6622 patterns succeeds, but failure to match later in the pattern causes 6623 backtracking over this assertion, the captures within the assertion are 6624 reset only if no higher numbered captures are already set. This is, 6625 unfortunately, a fundamental limitation of the current implementation, 6626 and as PCRE1 is now in maintenance-only status, it is unlikely ever to 6627 change. 6628 6629 For compatibility with Perl, assertion subpatterns may be repeated; 6630 though it makes no sense to assert the same thing several times, the 6631 side effect of capturing parentheses may occasionally be useful. In 6632 practice, there only three cases: 6633 6634 (1) If the quantifier is {0}, the assertion is never obeyed during 6635 matching. However, it may contain internal capturing parenthesized 6636 groups that are called from elsewhere via the subroutine mechanism. 6637 6638 (2) If quantifier is {0,n} where n is greater than zero, it is treated 6639 as if it were {0,1}. At run time, the rest of the pattern match is 6640 tried with and without the assertion, the order depending on the greed- 6641 iness of the quantifier. 6642 6643 (3) If the minimum repetition is greater than zero, the quantifier is 6644 ignored. The assertion is obeyed just once when encountered during 6645 matching. 6646 6647 Lookahead assertions 6648 6649 Lookahead assertions start with (?= for positive assertions and (?! for 6650 negative assertions. For example, 6651 6652 \w+(?=;) 6653 6654 matches a word followed by a semicolon, but does not include the semi- 6655 colon in the match, and 6656 6657 foo(?!bar) 6658 6659 matches any occurrence of "foo" that is not followed by "bar". Note 6660 that the apparently similar pattern 6661 6662 (?!foo)bar 6663 6664 does not find an occurrence of "bar" that is preceded by something 6665 other than "foo"; it finds any occurrence of "bar" whatsoever, because 6666 the assertion (?!foo) is always true when the next three characters are 6667 "bar". A lookbehind assertion is needed to achieve the other effect. 6668 6669 If you want to force a matching failure at some point in a pattern, the 6670 most convenient way to do it is with (?!) because an empty string 6671 always matches, so an assertion that requires there not to be an empty 6672 string must always fail. The backtracking control verb (*FAIL) or (*F) 6673 is a synonym for (?!). 6674 6675 Lookbehind assertions 6676 6677 Lookbehind assertions start with (?<= for positive assertions and (?<! 6678 for negative assertions. For example, 6679 6680 (?<!foo)bar 6681 6682 does find an occurrence of "bar" that is not preceded by "foo". The 6683 contents of a lookbehind assertion are restricted such that all the 6684 strings it matches must have a fixed length. However, if there are sev- 6685 eral top-level alternatives, they do not all have to have the same 6686 fixed length. Thus 6687 6688 (?<=bullock|donkey) 6689 6690 is permitted, but 6691 6692 (?<!dogs?|cats?) 6693 6694 causes an error at compile time. Branches that match different length 6695 strings are permitted only at the top level of a lookbehind assertion. 6696 This is an extension compared with Perl, which requires all branches to 6697 match the same length of string. An assertion such as 6698 6699 (?<=ab(c|de)) 6700 6701 is not permitted, because its single top-level branch can match two 6702 different lengths, but it is acceptable to PCRE if rewritten to use two 6703 top-level branches: 6704 6705 (?<=abc|abde) 6706 6707 In some cases, the escape sequence \K (see above) can be used instead 6708 of a lookbehind assertion to get round the fixed-length restriction. 6709 6710 The implementation of lookbehind assertions is, for each alternative, 6711 to temporarily move the current position back by the fixed length and 6712 then try to match. If there are insufficient characters before the cur- 6713 rent position, the assertion fails. 6714 6715 In a UTF mode, PCRE does not allow the \C escape (which matches a sin- 6716 gle data unit even in a UTF mode) to appear in lookbehind assertions, 6717 because it makes it impossible to calculate the length of the lookbe- 6718 hind. The \X and \R escapes, which can match different numbers of data 6719 units, are also not permitted. 6720 6721 "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in 6722 lookbehinds, as long as the subpattern matches a fixed-length string. 6723 Recursion, however, is not supported. 6724 6725 Possessive quantifiers can be used in conjunction with lookbehind 6726 assertions to specify efficient matching of fixed-length strings at the 6727 end of subject strings. Consider a simple pattern such as 6728 6729 abcd$ 6730 6731 when applied to a long string that does not match. Because matching 6732 proceeds from left to right, PCRE will look for each "a" in the subject 6733 and then see if what follows matches the rest of the pattern. If the 6734 pattern is specified as 6735 6736 ^.*abcd$ 6737 6738 the initial .* matches the entire string at first, but when this fails 6739 (because there is no following "a"), it backtracks to match all but the 6740 last character, then all but the last two characters, and so on. Once 6741 again the search for "a" covers the entire string, from right to left, 6742 so we are no better off. However, if the pattern is written as 6743 6744 ^.*+(?<=abcd) 6745 6746 there can be no backtracking for the .*+ item; it can match only the 6747 entire string. The subsequent lookbehind assertion does a single test 6748 on the last four characters. If it fails, the match fails immediately. 6749 For long strings, this approach makes a significant difference to the 6750 processing time. 6751 6752 Using multiple assertions 6753 6754 Several assertions (of any sort) may occur in succession. For example, 6755 6756 (?<=\d{3})(?<!999)foo 6757 6758 matches "foo" preceded by three digits that are not "999". Notice that 6759 each of the assertions is applied independently at the same point in 6760 the subject string. First there is a check that the previous three 6761 characters are all digits, and then there is a check that the same 6762 three characters are not "999". This pattern does not match "foo" pre- 6763 ceded by six characters, the first of which are digits and the last 6764 three of which are not "999". For example, it doesn't match "123abc- 6765 foo". A pattern to do that is 6766 6767 (?<=\d{3}...)(?<!999)foo 6768 6769 This time the first assertion looks at the preceding six characters, 6770 checking that the first three are digits, and then the second assertion 6771 checks that the preceding three characters are not "999". 6772 6773 Assertions can be nested in any combination. For example, 6774 6775 (?<=(?<!foo)bar)baz 6776 6777 matches an occurrence of "baz" that is preceded by "bar" which in turn 6778 is not preceded by "foo", while 6779 6780 (?<=\d{3}(?!999)...)foo 6781 6782 is another pattern that matches "foo" preceded by three digits and any 6783 three characters that are not "999". 6784 6785 6786CONDITIONAL SUBPATTERNS 6787 6788 It is possible to cause the matching process to obey a subpattern con- 6789 ditionally or to choose between two alternative subpatterns, depending 6790 on the result of an assertion, or whether a specific capturing subpat- 6791 tern has already been matched. The two possible forms of conditional 6792 subpattern are: 6793 6794 (?(condition)yes-pattern) 6795 (?(condition)yes-pattern|no-pattern) 6796 6797 If the condition is satisfied, the yes-pattern is used; otherwise the 6798 no-pattern (if present) is used. If there are more than two alterna- 6799 tives in the subpattern, a compile-time error occurs. Each of the two 6800 alternatives may itself contain nested subpatterns of any form, includ- 6801 ing conditional subpatterns; the restriction to two alternatives 6802 applies only at the level of the condition. This pattern fragment is an 6803 example where the alternatives are complex: 6804 6805 (?(1) (A|B|C) | (D | (?(2)E|F) | E) ) 6806 6807 6808 There are four kinds of condition: references to subpatterns, refer- 6809 ences to recursion, a pseudo-condition called DEFINE, and assertions. 6810 6811 Checking for a used subpattern by number 6812 6813 If the text between the parentheses consists of a sequence of digits, 6814 the condition is true if a capturing subpattern of that number has pre- 6815 viously matched. If there is more than one capturing subpattern with 6816 the same number (see the earlier section about duplicate subpattern 6817 numbers), the condition is true if any of them have matched. An alter- 6818 native notation is to precede the digits with a plus or minus sign. In 6819 this case, the subpattern number is relative rather than absolute. The 6820 most recently opened parentheses can be referenced by (?(-1), the next 6821 most recent by (?(-2), and so on. Inside loops it can also make sense 6822 to refer to subsequent groups. The next parentheses to be opened can be 6823 referenced as (?(+1), and so on. (The value zero in any of these forms 6824 is not used; it provokes a compile-time error.) 6825 6826 Consider the following pattern, which contains non-significant white 6827 space to make it more readable (assume the PCRE_EXTENDED option) and to 6828 divide it into three parts for ease of discussion: 6829 6830 ( \( )? [^()]+ (?(1) \) ) 6831 6832 The first part matches an optional opening parenthesis, and if that 6833 character is present, sets it as the first captured substring. The sec- 6834 ond part matches one or more characters that are not parentheses. The 6835 third part is a conditional subpattern that tests whether or not the 6836 first set of parentheses matched. If they did, that is, if subject 6837 started with an opening parenthesis, the condition is true, and so the 6838 yes-pattern is executed and a closing parenthesis is required. Other- 6839 wise, since no-pattern is not present, the subpattern matches nothing. 6840 In other words, this pattern matches a sequence of non-parentheses, 6841 optionally enclosed in parentheses. 6842 6843 If you were embedding this pattern in a larger one, you could use a 6844 relative reference: 6845 6846 ...other stuff... ( \( )? [^()]+ (?(-1) \) ) ... 6847 6848 This makes the fragment independent of the parentheses in the larger 6849 pattern. 6850 6851 Checking for a used subpattern by name 6852 6853 Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a 6854 used subpattern by name. For compatibility with earlier versions of 6855 PCRE, which had this facility before Perl, the syntax (?(name)...) is 6856 also recognized. 6857 6858 Rewriting the above example to use a named subpattern gives this: 6859 6860 (?<OPEN> \( )? [^()]+ (?(<OPEN>) \) ) 6861 6862 If the name used in a condition of this kind is a duplicate, the test 6863 is applied to all subpatterns of the same name, and is true if any one 6864 of them has matched. 6865 6866 Checking for pattern recursion 6867 6868 If the condition is the string (R), and there is no subpattern with the 6869 name R, the condition is true if a recursive call to the whole pattern 6870 or any subpattern has been made. If digits or a name preceded by amper- 6871 sand follow the letter R, for example: 6872 6873 (?(R3)...) or (?(R&name)...) 6874 6875 the condition is true if the most recent recursion is into a subpattern 6876 whose number or name is given. This condition does not check the entire 6877 recursion stack. If the name used in a condition of this kind is a 6878 duplicate, the test is applied to all subpatterns of the same name, and 6879 is true if any one of them is the most recent recursion. 6880 6881 At "top level", all these recursion test conditions are false. The 6882 syntax for recursive patterns is described below. 6883 6884 Defining subpatterns for use by reference only 6885 6886 If the condition is the string (DEFINE), and there is no subpattern 6887 with the name DEFINE, the condition is always false. In this case, 6888 there may be only one alternative in the subpattern. It is always 6889 skipped if control reaches this point in the pattern; the idea of 6890 DEFINE is that it can be used to define subroutines that can be refer- 6891 enced from elsewhere. (The use of subroutines is described below.) For 6892 example, a pattern to match an IPv4 address such as "192.168.23.245" 6893 could be written like this (ignore white space and line breaks): 6894 6895 (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) ) 6896 \b (?&byte) (\.(?&byte)){3} \b 6897 6898 The first part of the pattern is a DEFINE group inside which a another 6899 group named "byte" is defined. This matches an individual component of 6900 an IPv4 address (a number less than 256). When matching takes place, 6901 this part of the pattern is skipped because DEFINE acts like a false 6902 condition. The rest of the pattern uses references to the named group 6903 to match the four dot-separated components of an IPv4 address, insist- 6904 ing on a word boundary at each end. 6905 6906 Assertion conditions 6907 6908 If the condition is not in any of the above formats, it must be an 6909 assertion. This may be a positive or negative lookahead or lookbehind 6910 assertion. Consider this pattern, again containing non-significant 6911 white space, and with the two alternatives on the second line: 6912 6913 (?(?=[^a-z]*[a-z]) 6914 \d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} ) 6915 6916 The condition is a positive lookahead assertion that matches an 6917 optional sequence of non-letters followed by a letter. In other words, 6918 it tests for the presence of at least one letter in the subject. If a 6919 letter is found, the subject is matched against the first alternative; 6920 otherwise it is matched against the second. This pattern matches 6921 strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are 6922 letters and dd are digits. 6923 6924 6925COMMENTS 6926 6927 There are two ways of including comments in patterns that are processed 6928 by PCRE. In both cases, the start of the comment must not be in a char- 6929 acter class, nor in the middle of any other sequence of related charac- 6930 ters such as (?: or a subpattern name or number. The characters that 6931 make up a comment play no part in the pattern matching. 6932 6933 The sequence (?# marks the start of a comment that continues up to the 6934 next closing parenthesis. Nested parentheses are not permitted. If the 6935 PCRE_EXTENDED option is set, an unescaped # character also introduces a 6936 comment, which in this case continues to immediately after the next 6937 newline character or character sequence in the pattern. Which charac- 6938 ters are interpreted as newlines is controlled by the options passed to 6939 a compiling function or by a special sequence at the start of the pat- 6940 tern, as described in the section entitled "Newline conventions" above. 6941 Note that the end of this type of comment is a literal newline sequence 6942 in the pattern; escape sequences that happen to represent a newline do 6943 not count. For example, consider this pattern when PCRE_EXTENDED is 6944 set, and the default newline convention is in force: 6945 6946 abc #comment \n still comment 6947 6948 On encountering the # character, pcre_compile() skips along, looking 6949 for a newline in the pattern. The sequence \n is still literal at this 6950 stage, so it does not terminate the comment. Only an actual character 6951 with the code value 0x0a (the default newline) does so. 6952 6953 6954RECURSIVE PATTERNS 6955 6956 Consider the problem of matching a string in parentheses, allowing for 6957 unlimited nested parentheses. Without the use of recursion, the best 6958 that can be done is to use a pattern that matches up to some fixed 6959 depth of nesting. It is not possible to handle an arbitrary nesting 6960 depth. 6961 6962 For some time, Perl has provided a facility that allows regular expres- 6963 sions to recurse (amongst other things). It does this by interpolating 6964 Perl code in the expression at run time, and the code can refer to the 6965 expression itself. A Perl pattern using code interpolation to solve the 6966 parentheses problem can be created like this: 6967 6968 $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x; 6969 6970 The (?p{...}) item interpolates Perl code at run time, and in this case 6971 refers recursively to the pattern in which it appears. 6972 6973 Obviously, PCRE cannot support the interpolation of Perl code. Instead, 6974 it supports special syntax for recursion of the entire pattern, and 6975 also for individual subpattern recursion. After its introduction in 6976 PCRE and Python, this kind of recursion was subsequently introduced 6977 into Perl at release 5.10. 6978 6979 A special item that consists of (? followed by a number greater than 6980 zero and a closing parenthesis is a recursive subroutine call of the 6981 subpattern of the given number, provided that it occurs inside that 6982 subpattern. (If not, it is a non-recursive subroutine call, which is 6983 described in the next section.) The special item (?R) or (?0) is a 6984 recursive call of the entire regular expression. 6985 6986 This PCRE pattern solves the nested parentheses problem (assume the 6987 PCRE_EXTENDED option is set so that white space is ignored): 6988 6989 \( ( [^()]++ | (?R) )* \) 6990 6991 First it matches an opening parenthesis. Then it matches any number of 6992 substrings which can either be a sequence of non-parentheses, or a 6993 recursive match of the pattern itself (that is, a correctly parenthe- 6994 sized substring). Finally there is a closing parenthesis. Note the use 6995 of a possessive quantifier to avoid backtracking into sequences of non- 6996 parentheses. 6997 6998 If this were part of a larger pattern, you would not want to recurse 6999 the entire pattern, so instead you could use this: 7000 7001 ( \( ( [^()]++ | (?1) )* \) ) 7002 7003 We have put the pattern into parentheses, and caused the recursion to 7004 refer to them instead of the whole pattern. 7005 7006 In a larger pattern, keeping track of parenthesis numbers can be 7007 tricky. This is made easier by the use of relative references. Instead 7008 of (?1) in the pattern above you can write (?-2) to refer to the second 7009 most recently opened parentheses preceding the recursion. In other 7010 words, a negative number counts capturing parentheses leftwards from 7011 the point at which it is encountered. 7012 7013 It is also possible to refer to subsequently opened parentheses, by 7014 writing references such as (?+2). However, these cannot be recursive 7015 because the reference is not inside the parentheses that are refer- 7016 enced. They are always non-recursive subroutine calls, as described in 7017 the next section. 7018 7019 An alternative approach is to use named parentheses instead. The Perl 7020 syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also 7021 supported. We could rewrite the above example as follows: 7022 7023 (?<pn> \( ( [^()]++ | (?&pn) )* \) ) 7024 7025 If there is more than one subpattern with the same name, the earliest 7026 one is used. 7027 7028 This particular example pattern that we have been looking at contains 7029 nested unlimited repeats, and so the use of a possessive quantifier for 7030 matching strings of non-parentheses is important when applying the pat- 7031 tern to strings that do not match. For example, when this pattern is 7032 applied to 7033 7034 (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa() 7035 7036 it yields "no match" quickly. However, if a possessive quantifier is 7037 not used, the match runs for a very long time indeed because there are 7038 so many different ways the + and * repeats can carve up the subject, 7039 and all have to be tested before failure can be reported. 7040 7041 At the end of a match, the values of capturing parentheses are those 7042 from the outermost level. If you want to obtain intermediate values, a 7043 callout function can be used (see below and the pcrecallout documenta- 7044 tion). If the pattern above is matched against 7045 7046 (ab(cd)ef) 7047 7048 the value for the inner capturing parentheses (numbered 2) is "ef", 7049 which is the last value taken on at the top level. If a capturing sub- 7050 pattern is not matched at the top level, its final captured value is 7051 unset, even if it was (temporarily) set at a deeper level during the 7052 matching process. 7053 7054 If there are more than 15 capturing parentheses in a pattern, PCRE has 7055 to obtain extra memory to store data during a recursion, which it does 7056 by using pcre_malloc, freeing it via pcre_free afterwards. If no memory 7057 can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error. 7058 7059 Do not confuse the (?R) item with the condition (R), which tests for 7060 recursion. Consider this pattern, which matches text in angle brack- 7061 ets, allowing for arbitrary nesting. Only digits are allowed in nested 7062 brackets (that is, when recursing), whereas any characters are permit- 7063 ted at the outer level. 7064 7065 < (?: (?(R) \d++ | [^<>]*+) | (?R)) * > 7066 7067 In this pattern, (?(R) is the start of a conditional subpattern, with 7068 two different alternatives for the recursive and non-recursive cases. 7069 The (?R) item is the actual recursive call. 7070 7071 Differences in recursion processing between PCRE and Perl 7072 7073 Recursion processing in PCRE differs from Perl in two important ways. 7074 In PCRE (like Python, but unlike Perl), a recursive subpattern call is 7075 always treated as an atomic group. That is, once it has matched some of 7076 the subject string, it is never re-entered, even if it contains untried 7077 alternatives and there is a subsequent matching failure. This can be 7078 illustrated by the following pattern, which purports to match a palin- 7079 dromic string that contains an odd number of characters (for example, 7080 "a", "aba", "abcba", "abcdcba"): 7081 7082 ^(.|(.)(?1)\2)$ 7083 7084 The idea is that it either matches a single character, or two identical 7085 characters surrounding a sub-palindrome. In Perl, this pattern works; 7086 in PCRE it does not if the pattern is longer than three characters. 7087 Consider the subject string "abcba": 7088 7089 At the top level, the first character is matched, but as it is not at 7090 the end of the string, the first alternative fails; the second alterna- 7091 tive is taken and the recursion kicks in. The recursive call to subpat- 7092 tern 1 successfully matches the next character ("b"). (Note that the 7093 beginning and end of line tests are not part of the recursion). 7094 7095 Back at the top level, the next character ("c") is compared with what 7096 subpattern 2 matched, which was "a". This fails. Because the recursion 7097 is treated as an atomic group, there are now no backtracking points, 7098 and so the entire match fails. (Perl is able, at this point, to re- 7099 enter the recursion and try the second alternative.) However, if the 7100 pattern is written with the alternatives in the other order, things are 7101 different: 7102 7103 ^((.)(?1)\2|.)$ 7104 7105 This time, the recursing alternative is tried first, and continues to 7106 recurse until it runs out of characters, at which point the recursion 7107 fails. But this time we do have another alternative to try at the 7108 higher level. That is the big difference: in the previous case the 7109 remaining alternative is at a deeper recursion level, which PCRE cannot 7110 use. 7111 7112 To change the pattern so that it matches all palindromic strings, not 7113 just those with an odd number of characters, it is tempting to change 7114 the pattern to this: 7115 7116 ^((.)(?1)\2|.?)$ 7117 7118 Again, this works in Perl, but not in PCRE, and for the same reason. 7119 When a deeper recursion has matched a single character, it cannot be 7120 entered again in order to match an empty string. The solution is to 7121 separate the two cases, and write out the odd and even cases as alter- 7122 natives at the higher level: 7123 7124 ^(?:((.)(?1)\2|)|((.)(?3)\4|.)) 7125 7126 If you want to match typical palindromic phrases, the pattern has to 7127 ignore all non-word characters, which can be done like this: 7128 7129 ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$ 7130 7131 If run with the PCRE_CASELESS option, this pattern matches phrases such 7132 as "A man, a plan, a canal: Panama!" and it works well in both PCRE and 7133 Perl. Note the use of the possessive quantifier *+ to avoid backtrack- 7134 ing into sequences of non-word characters. Without this, PCRE takes a 7135 great deal longer (ten times or more) to match typical phrases, and 7136 Perl takes so long that you think it has gone into a loop. 7137 7138 WARNING: The palindrome-matching patterns above work only if the sub- 7139 ject string does not start with a palindrome that is shorter than the 7140 entire string. For example, although "abcba" is correctly matched, if 7141 the subject is "ababa", PCRE finds the palindrome "aba" at the start, 7142 then fails at top level because the end of the string does not follow. 7143 Once again, it cannot jump back into the recursion to try other alter- 7144 natives, so the entire match fails. 7145 7146 The second way in which PCRE and Perl differ in their recursion pro- 7147 cessing is in the handling of captured values. In Perl, when a subpat- 7148 tern is called recursively or as a subpattern (see the next section), 7149 it has no access to any values that were captured outside the recur- 7150 sion, whereas in PCRE these values can be referenced. Consider this 7151 pattern: 7152 7153 ^(.)(\1|a(?2)) 7154 7155 In PCRE, this pattern matches "bab". The first capturing parentheses 7156 match "b", then in the second group, when the back reference \1 fails 7157 to match "b", the second alternative matches "a" and then recurses. In 7158 the recursion, \1 does now match "b" and so the whole match succeeds. 7159 In Perl, the pattern fails to match because inside the recursive call 7160 \1 cannot access the externally set value. 7161 7162 7163SUBPATTERNS AS SUBROUTINES 7164 7165 If the syntax for a recursive subpattern call (either by number or by 7166 name) is used outside the parentheses to which it refers, it operates 7167 like a subroutine in a programming language. The called subpattern may 7168 be defined before or after the reference. A numbered reference can be 7169 absolute or relative, as in these examples: 7170 7171 (...(absolute)...)...(?2)... 7172 (...(relative)...)...(?-1)... 7173 (...(?+1)...(relative)... 7174 7175 An earlier example pointed out that the pattern 7176 7177 (sens|respons)e and \1ibility 7178 7179 matches "sense and sensibility" and "response and responsibility", but 7180 not "sense and responsibility". If instead the pattern 7181 7182 (sens|respons)e and (?1)ibility 7183 7184 is used, it does match "sense and responsibility" as well as the other 7185 two strings. Another example is given in the discussion of DEFINE 7186 above. 7187 7188 All subroutine calls, whether recursive or not, are always treated as 7189 atomic groups. That is, once a subroutine has matched some of the sub- 7190 ject string, it is never re-entered, even if it contains untried alter- 7191 natives and there is a subsequent matching failure. Any capturing 7192 parentheses that are set during the subroutine call revert to their 7193 previous values afterwards. 7194 7195 Processing options such as case-independence are fixed when a subpat- 7196 tern is defined, so if it is used as a subroutine, such options cannot 7197 be changed for different calls. For example, consider this pattern: 7198 7199 (abc)(?i:(?-1)) 7200 7201 It matches "abcabc". It does not match "abcABC" because the change of 7202 processing option does not affect the called subpattern. 7203 7204 7205ONIGURUMA SUBROUTINE SYNTAX 7206 7207 For compatibility with Oniguruma, the non-Perl syntax \g followed by a 7208 name or a number enclosed either in angle brackets or single quotes, is 7209 an alternative syntax for referencing a subpattern as a subroutine, 7210 possibly recursively. Here are two of the examples used above, rewrit- 7211 ten using this syntax: 7212 7213 (?<pn> \( ( (?>[^()]+) | \g<pn> )* \) ) 7214 (sens|respons)e and \g'1'ibility 7215 7216 PCRE supports an extension to Oniguruma: if a number is preceded by a 7217 plus or a minus sign it is taken as a relative reference. For example: 7218 7219 (abc)(?i:\g<-1>) 7220 7221 Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not 7222 synonymous. The former is a back reference; the latter is a subroutine 7223 call. 7224 7225 7226CALLOUTS 7227 7228 Perl has a feature whereby using the sequence (?{...}) causes arbitrary 7229 Perl code to be obeyed in the middle of matching a regular expression. 7230 This makes it possible, amongst other things, to extract different sub- 7231 strings that match the same pair of parentheses when there is a repeti- 7232 tion. 7233 7234 PCRE provides a similar feature, but of course it cannot obey arbitrary 7235 Perl code. The feature is called "callout". The caller of PCRE provides 7236 an external function by putting its entry point in the global variable 7237 pcre_callout (8-bit library) or pcre[16|32]_callout (16-bit or 32-bit 7238 library). By default, this variable contains NULL, which disables all 7239 calling out. 7240 7241 Within a regular expression, (?C) indicates the points at which the 7242 external function is to be called. If you want to identify different 7243 callout points, you can put a number less than 256 after the letter C. 7244 The default value is zero. For example, this pattern has two callout 7245 points: 7246 7247 (?C1)abc(?C2)def 7248 7249 If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, call- 7250 outs are automatically installed before each item in the pattern. They 7251 are all numbered 255. If there is a conditional group in the pattern 7252 whose condition is an assertion, an additional callout is inserted just 7253 before the condition. An explicit callout may also be set at this posi- 7254 tion, as in this example: 7255 7256 (?(?C9)(?=a)abc|def) 7257 7258 Note that this applies only to assertion conditions, not to other types 7259 of condition. 7260 7261 During matching, when PCRE reaches a callout point, the external func- 7262 tion is called. It is provided with the number of the callout, the 7263 position in the pattern, and, optionally, one item of data originally 7264 supplied by the caller of the matching function. The callout function 7265 may cause matching to proceed, to backtrack, or to fail altogether. 7266 7267 By default, PCRE implements a number of optimizations at compile time 7268 and matching time, and one side-effect is that sometimes callouts are 7269 skipped. If you need all possible callouts to happen, you need to set 7270 options that disable the relevant optimizations. More details, and a 7271 complete description of the interface to the callout function, are 7272 given in the pcrecallout documentation. 7273 7274 7275BACKTRACKING CONTROL 7276 7277 Perl 5.10 introduced a number of "Special Backtracking Control Verbs", 7278 which are still described in the Perl documentation as "experimental 7279 and subject to change or removal in a future version of Perl". It goes 7280 on to say: "Their usage in production code should be noted to avoid 7281 problems during upgrades." The same remarks apply to the PCRE features 7282 described in this section. 7283 7284 The new verbs make use of what was previously invalid syntax: an open- 7285 ing parenthesis followed by an asterisk. They are generally of the form 7286 (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving 7287 differently depending on whether or not a name is present. A name is 7288 any sequence of characters that does not include a closing parenthesis. 7289 The maximum length of name is 255 in the 8-bit library and 65535 in the 7290 16-bit and 32-bit libraries. If the name is empty, that is, if the 7291 closing parenthesis immediately follows the colon, the effect is as if 7292 the colon were not there. Any number of these verbs may occur in a 7293 pattern. 7294 7295 Since these verbs are specifically related to backtracking, most of 7296 them can be used only when the pattern is to be matched using one of 7297 the traditional matching functions, because these use a backtracking 7298 algorithm. With the exception of (*FAIL), which behaves like a failing 7299 negative assertion, the backtracking control verbs cause an error if 7300 encountered by a DFA matching function. 7301 7302 The behaviour of these verbs in repeated groups, assertions, and in 7303 subpatterns called as subroutines (whether or not recursively) is docu- 7304 mented below. 7305 7306 Optimizations that affect backtracking verbs 7307 7308 PCRE contains some optimizations that are used to speed up matching by 7309 running some checks at the start of each match attempt. For example, it 7310 may know the minimum length of matching subject, or that a particular 7311 character must be present. When one of these optimizations bypasses the 7312 running of a match, any included backtracking verbs will not, of 7313 course, be processed. You can suppress the start-of-match optimizations 7314 by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_com- 7315 pile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT). 7316 There is more discussion of this option in the section entitled "Option 7317 bits for pcre_exec()" in the pcreapi documentation. 7318 7319 Experiments with Perl suggest that it too has similar optimizations, 7320 sometimes leading to anomalous results. 7321 7322 Verbs that act immediately 7323 7324 The following verbs act as soon as they are encountered. They may not 7325 be followed by a name. 7326 7327 (*ACCEPT) 7328 7329 This verb causes the match to end successfully, skipping the remainder 7330 of the pattern. However, when it is inside a subpattern that is called 7331 as a subroutine, only that subpattern is ended successfully. Matching 7332 then continues at the outer level. If (*ACCEPT) in triggered in a posi- 7333 tive assertion, the assertion succeeds; in a negative assertion, the 7334 assertion fails. 7335 7336 If (*ACCEPT) is inside capturing parentheses, the data so far is cap- 7337 tured. For example: 7338 7339 A((?:A|B(*ACCEPT)|C)D) 7340 7341 This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- 7342 tured by the outer parentheses. 7343 7344 (*FAIL) or (*F) 7345 7346 This verb causes a matching failure, forcing backtracking to occur. It 7347 is equivalent to (?!) but easier to read. The Perl documentation notes 7348 that it is probably useful only when combined with (?{}) or (??{}). 7349 Those are, of course, Perl features that are not present in PCRE. The 7350 nearest equivalent is the callout feature, as for example in this pat- 7351 tern: 7352 7353 a+(?C)(*FAIL) 7354 7355 A match with the string "aaaa" always fails, but the callout is taken 7356 before each backtrack happens (in this example, 10 times). 7357 7358 Recording which path was taken 7359 7360 There is one verb whose main purpose is to track how a match was 7361 arrived at, though it also has a secondary use in conjunction with 7362 advancing the match starting point (see (*SKIP) below). 7363 7364 (*MARK:NAME) or (*:NAME) 7365 7366 A name is always required with this verb. There may be as many 7367 instances of (*MARK) as you like in a pattern, and their names do not 7368 have to be unique. 7369 7370 When a match succeeds, the name of the last-encountered (*MARK:NAME), 7371 (*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to 7372 the caller as described in the section entitled "Extra data for 7373 pcre_exec()" in the pcreapi documentation. Here is an example of 7374 pcretest output, where the /K modifier requests the retrieval and out- 7375 putting of (*MARK) data: 7376 7377 re> /X(*MARK:A)Y|X(*MARK:B)Z/K 7378 data> XY 7379 0: XY 7380 MK: A 7381 XZ 7382 0: XZ 7383 MK: B 7384 7385 The (*MARK) name is tagged with "MK:" in this output, and in this exam- 7386 ple it indicates which of the two alternatives matched. This is a more 7387 efficient way of obtaining this information than putting each alterna- 7388 tive in its own capturing parentheses. 7389 7390 If a verb with a name is encountered in a positive assertion that is 7391 true, the name is recorded and passed back if it is the last-encoun- 7392 tered. This does not happen for negative assertions or failing positive 7393 assertions. 7394 7395 After a partial match or a failed match, the last encountered name in 7396 the entire match process is returned. For example: 7397 7398 re> /X(*MARK:A)Y|X(*MARK:B)Z/K 7399 data> XP 7400 No match, mark = B 7401 7402 Note that in this unanchored example the mark is retained from the 7403 match attempt that started at the letter "X" in the subject. Subsequent 7404 match attempts starting at "P" and then with an empty string do not get 7405 as far as the (*MARK) item, but nevertheless do not reset it. 7406 7407 If you are interested in (*MARK) values after failed matches, you 7408 should probably set the PCRE_NO_START_OPTIMIZE option (see above) to 7409 ensure that the match is always attempted. 7410 7411 Verbs that act after backtracking 7412 7413 The following verbs do nothing when they are encountered. Matching con- 7414 tinues with what follows, but if there is no subsequent match, causing 7415 a backtrack to the verb, a failure is forced. That is, backtracking 7416 cannot pass to the left of the verb. However, when one of these verbs 7417 appears inside an atomic group or an assertion that is true, its effect 7418 is confined to that group, because once the group has been matched, 7419 there is never any backtracking into it. In this situation, backtrack- 7420 ing can "jump back" to the left of the entire atomic group or asser- 7421 tion. (Remember also, as stated above, that this localization also 7422 applies in subroutine calls.) 7423 7424 These verbs differ in exactly what kind of failure occurs when back- 7425 tracking reaches them. The behaviour described below is what happens 7426 when the verb is not in a subroutine or an assertion. Subsequent sec- 7427 tions cover these special cases. 7428 7429 (*COMMIT) 7430 7431 This verb, which may not be followed by a name, causes the whole match 7432 to fail outright if there is a later matching failure that causes back- 7433 tracking to reach it. Even if the pattern is unanchored, no further 7434 attempts to find a match by advancing the starting point take place. If 7435 (*COMMIT) is the only backtracking verb that is encountered, once it 7436 has been passed pcre_exec() is committed to finding a match at the cur- 7437 rent starting point, or not at all. For example: 7438 7439 a+(*COMMIT)b 7440 7441 This matches "xxaab" but not "aacaab". It can be thought of as a kind 7442 of dynamic anchor, or "I've started, so I must finish." The name of the 7443 most recently passed (*MARK) in the path is passed back when (*COMMIT) 7444 forces a match failure. 7445 7446 If there is more than one backtracking verb in a pattern, a different 7447 one that follows (*COMMIT) may be triggered first, so merely passing 7448 (*COMMIT) during a match does not always guarantee that a match must be 7449 at this starting point. 7450 7451 Note that (*COMMIT) at the start of a pattern is not the same as an 7452 anchor, unless PCRE's start-of-match optimizations are turned off, as 7453 shown in this output from pcretest: 7454 7455 re> /(*COMMIT)abc/ 7456 data> xyzabc 7457 0: abc 7458 data> xyzabc\Y 7459 No match 7460 7461 For this pattern, PCRE knows that any match must start with "a", so the 7462 optimization skips along the subject to "a" before applying the pattern 7463 to the first set of data. The match attempt then succeeds. In the sec- 7464 ond set of data, the escape sequence \Y is interpreted by the pcretest 7465 program. It causes the PCRE_NO_START_OPTIMIZE option to be set when 7466 pcre_exec() is called. This disables the optimization that skips along 7467 to the first character. The pattern is now applied starting at "x", and 7468 so the (*COMMIT) causes the match to fail without trying any other 7469 starting points. 7470 7471 (*PRUNE) or (*PRUNE:NAME) 7472 7473 This verb causes the match to fail at the current starting position in 7474 the subject if there is a later matching failure that causes backtrack- 7475 ing to reach it. If the pattern is unanchored, the normal "bumpalong" 7476 advance to the next starting character then happens. Backtracking can 7477 occur as usual to the left of (*PRUNE), before it is reached, or when 7478 matching to the right of (*PRUNE), but if there is no match to the 7479 right, backtracking cannot cross (*PRUNE). In simple cases, the use of 7480 (*PRUNE) is just an alternative to an atomic group or possessive quan- 7481 tifier, but there are some uses of (*PRUNE) that cannot be expressed in 7482 any other way. In an anchored pattern (*PRUNE) has the same effect as 7483 (*COMMIT). 7484 7485 The behaviour of (*PRUNE:NAME) is the not the same as 7486 (*MARK:NAME)(*PRUNE). It is like (*MARK:NAME) in that the name is 7487 remembered for passing back to the caller. However, (*SKIP:NAME) 7488 searches only for names set with (*MARK). 7489 7490 (*SKIP) 7491 7492 This verb, when given without a name, is like (*PRUNE), except that if 7493 the pattern is unanchored, the "bumpalong" advance is not to the next 7494 character, but to the position in the subject where (*SKIP) was encoun- 7495 tered. (*SKIP) signifies that whatever text was matched leading up to 7496 it cannot be part of a successful match. Consider: 7497 7498 a+(*SKIP)b 7499 7500 If the subject is "aaaac...", after the first match attempt fails 7501 (starting at the first character in the string), the starting point 7502 skips on to start the next attempt at "c". Note that a possessive quan- 7503 tifer does not have the same effect as this example; although it would 7504 suppress backtracking during the first match attempt, the second 7505 attempt would start at the second character instead of skipping on to 7506 "c". 7507 7508 (*SKIP:NAME) 7509 7510 When (*SKIP) has an associated name, its behaviour is modified. When it 7511 is triggered, the previous path through the pattern is searched for the 7512 most recent (*MARK) that has the same name. If one is found, the 7513 "bumpalong" advance is to the subject position that corresponds to that 7514 (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with 7515 a matching name is found, the (*SKIP) is ignored. 7516 7517 Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It 7518 ignores names that are set by (*PRUNE:NAME) or (*THEN:NAME). 7519 7520 (*THEN) or (*THEN:NAME) 7521 7522 This verb causes a skip to the next innermost alternative when back- 7523 tracking reaches it. That is, it cancels any further backtracking 7524 within the current alternative. Its name comes from the observation 7525 that it can be used for a pattern-based if-then-else block: 7526 7527 ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ... 7528 7529 If the COND1 pattern matches, FOO is tried (and possibly further items 7530 after the end of the group if FOO succeeds); on failure, the matcher 7531 skips to the second alternative and tries COND2, without backtracking 7532 into COND1. If that succeeds and BAR fails, COND3 is tried. If subse- 7533 quently BAZ fails, there are no more alternatives, so there is a back- 7534 track to whatever came before the entire group. If (*THEN) is not 7535 inside an alternation, it acts like (*PRUNE). 7536 7537 The behaviour of (*THEN:NAME) is the not the same as 7538 (*MARK:NAME)(*THEN). It is like (*MARK:NAME) in that the name is 7539 remembered for passing back to the caller. However, (*SKIP:NAME) 7540 searches only for names set with (*MARK). 7541 7542 A subpattern that does not contain a | character is just a part of the 7543 enclosing alternative; it is not a nested alternation with only one 7544 alternative. The effect of (*THEN) extends beyond such a subpattern to 7545 the enclosing alternative. Consider this pattern, where A, B, etc. are 7546 complex pattern fragments that do not contain any | characters at this 7547 level: 7548 7549 A (B(*THEN)C) | D 7550 7551 If A and B are matched, but there is a failure in C, matching does not 7552 backtrack into A; instead it moves to the next alternative, that is, D. 7553 However, if the subpattern containing (*THEN) is given an alternative, 7554 it behaves differently: 7555 7556 A (B(*THEN)C | (*FAIL)) | D 7557 7558 The effect of (*THEN) is now confined to the inner subpattern. After a 7559 failure in C, matching moves to (*FAIL), which causes the whole subpat- 7560 tern to fail because there are no more alternatives to try. In this 7561 case, matching does now backtrack into A. 7562 7563 Note that a conditional subpattern is not considered as having two 7564 alternatives, because only one is ever used. In other words, the | 7565 character in a conditional subpattern has a different meaning. Ignoring 7566 white space, consider: 7567 7568 ^.*? (?(?=a) a | b(*THEN)c ) 7569 7570 If the subject is "ba", this pattern does not match. Because .*? is 7571 ungreedy, it initially matches zero characters. The condition (?=a) 7572 then fails, the character "b" is matched, but "c" is not. At this 7573 point, matching does not backtrack to .*? as might perhaps be expected 7574 from the presence of the | character. The conditional subpattern is 7575 part of the single alternative that comprises the whole pattern, and so 7576 the match fails. (If there was a backtrack into .*?, allowing it to 7577 match "b", the match would succeed.) 7578 7579 The verbs just described provide four different "strengths" of control 7580 when subsequent matching fails. (*THEN) is the weakest, carrying on the 7581 match at the next alternative. (*PRUNE) comes next, failing the match 7582 at the current starting position, but allowing an advance to the next 7583 character (for an unanchored pattern). (*SKIP) is similar, except that 7584 the advance may be more than one character. (*COMMIT) is the strongest, 7585 causing the entire match to fail. 7586 7587 More than one backtracking verb 7588 7589 If more than one backtracking verb is present in a pattern, the one 7590 that is backtracked onto first acts. For example, consider this pat- 7591 tern, where A, B, etc. are complex pattern fragments: 7592 7593 (A(*COMMIT)B(*THEN)C|ABD) 7594 7595 If A matches but B fails, the backtrack to (*COMMIT) causes the entire 7596 match to fail. However, if A and B match, but C fails, the backtrack to 7597 (*THEN) causes the next alternative (ABD) to be tried. This behaviour 7598 is consistent, but is not always the same as Perl's. It means that if 7599 two or more backtracking verbs appear in succession, all the the last 7600 of them has no effect. Consider this example: 7601 7602 ...(*COMMIT)(*PRUNE)... 7603 7604 If there is a matching failure to the right, backtracking onto (*PRUNE) 7605 causes it to be triggered, and its action is taken. There can never be 7606 a backtrack onto (*COMMIT). 7607 7608 Backtracking verbs in repeated groups 7609 7610 PCRE differs from Perl in its handling of backtracking verbs in 7611 repeated groups. For example, consider: 7612 7613 /(a(*COMMIT)b)+ac/ 7614 7615 If the subject is "abac", Perl matches, but PCRE fails because the 7616 (*COMMIT) in the second repeat of the group acts. 7617 7618 Backtracking verbs in assertions 7619 7620 (*FAIL) in an assertion has its normal effect: it forces an immediate 7621 backtrack. 7622 7623 (*ACCEPT) in a positive assertion causes the assertion to succeed with- 7624 out any further processing. In a negative assertion, (*ACCEPT) causes 7625 the assertion to fail without any further processing. 7626 7627 The other backtracking verbs are not treated specially if they appear 7628 in a positive assertion. In particular, (*THEN) skips to the next 7629 alternative in the innermost enclosing group that has alternations, 7630 whether or not this is within the assertion. 7631 7632 Negative assertions are, however, different, in order to ensure that 7633 changing a positive assertion into a negative assertion changes its 7634 result. Backtracking into (*COMMIT), (*SKIP), or (*PRUNE) causes a neg- 7635 ative assertion to be true, without considering any further alternative 7636 branches in the assertion. Backtracking into (*THEN) causes it to skip 7637 to the next enclosing alternative within the assertion (the normal be- 7638 haviour), but if the assertion does not have such an alternative, 7639 (*THEN) behaves like (*PRUNE). 7640 7641 Backtracking verbs in subroutines 7642 7643 These behaviours occur whether or not the subpattern is called recur- 7644 sively. Perl's treatment of subroutines is different in some cases. 7645 7646 (*FAIL) in a subpattern called as a subroutine has its normal effect: 7647 it forces an immediate backtrack. 7648 7649 (*ACCEPT) in a subpattern called as a subroutine causes the subroutine 7650 match to succeed without any further processing. Matching then contin- 7651 ues after the subroutine call. 7652 7653 (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine 7654 cause the subroutine match to fail. 7655 7656 (*THEN) skips to the next alternative in the innermost enclosing group 7657 within the subpattern that has alternatives. If there is no such group 7658 within the subpattern, (*THEN) causes the subroutine match to fail. 7659 7660 7661SEE ALSO 7662 7663 pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3), 7664 pcre16(3), pcre32(3). 7665 7666 7667AUTHOR 7668 7669 Philip Hazel 7670 University Computing Service 7671 Cambridge CB2 3QH, England. 7672 7673 7674REVISION 7675 7676 Last updated: 23 October 2016 7677 Copyright (c) 1997-2016 University of Cambridge. 7678------------------------------------------------------------------------------ 7679 7680 7681PCRESYNTAX(3) Library Functions Manual PCRESYNTAX(3) 7682 7683 7684 7685NAME 7686 PCRE - Perl-compatible regular expressions 7687 7688PCRE REGULAR EXPRESSION SYNTAX SUMMARY 7689 7690 The full syntax and semantics of the regular expressions that are sup- 7691 ported by PCRE are described in the pcrepattern documentation. This 7692 document contains a quick-reference summary of the syntax. 7693 7694 7695QUOTING 7696 7697 \x where x is non-alphanumeric is a literal x 7698 \Q...\E treat enclosed characters as literal 7699 7700 7701CHARACTERS 7702 7703 \a alarm, that is, the BEL character (hex 07) 7704 \cx "control-x", where x is any ASCII character 7705 \e escape (hex 1B) 7706 \f form feed (hex 0C) 7707 \n newline (hex 0A) 7708 \r carriage return (hex 0D) 7709 \t tab (hex 09) 7710 \0dd character with octal code 0dd 7711 \ddd character with octal code ddd, or backreference 7712 \o{ddd..} character with octal code ddd.. 7713 \xhh character with hex code hh 7714 \x{hhh..} character with hex code hhh.. 7715 7716 Note that \0dd is always an octal code, and that \8 and \9 are the lit- 7717 eral characters "8" and "9". 7718 7719 7720CHARACTER TYPES 7721 7722 . any character except newline; 7723 in dotall mode, any character whatsoever 7724 \C one data unit, even in UTF mode (best avoided) 7725 \d a decimal digit 7726 \D a character that is not a decimal digit 7727 \h a horizontal white space character 7728 \H a character that is not a horizontal white space character 7729 \N a character that is not a newline 7730 \p{xx} a character with the xx property 7731 \P{xx} a character without the xx property 7732 \R a newline sequence 7733 \s a white space character 7734 \S a character that is not a white space character 7735 \v a vertical white space character 7736 \V a character that is not a vertical white space character 7737 \w a "word" character 7738 \W a "non-word" character 7739 \X a Unicode extended grapheme cluster 7740 7741 By default, \d, \s, and \w match only ASCII characters, even in UTF-8 7742 mode or in the 16- bit and 32-bit libraries. However, if locale-spe- 7743 cific matching is happening, \s and \w may also match characters with 7744 code points in the range 128-255. If the PCRE_UCP option is set, the 7745 behaviour of these escape sequences is changed to use Unicode proper- 7746 ties and they match many more characters. 7747 7748 7749GENERAL CATEGORY PROPERTIES FOR \p and \P 7750 7751 C Other 7752 Cc Control 7753 Cf Format 7754 Cn Unassigned 7755 Co Private use 7756 Cs Surrogate 7757 7758 L Letter 7759 Ll Lower case letter 7760 Lm Modifier letter 7761 Lo Other letter 7762 Lt Title case letter 7763 Lu Upper case letter 7764 L& Ll, Lu, or Lt 7765 7766 M Mark 7767 Mc Spacing mark 7768 Me Enclosing mark 7769 Mn Non-spacing mark 7770 7771 N Number 7772 Nd Decimal number 7773 Nl Letter number 7774 No Other number 7775 7776 P Punctuation 7777 Pc Connector punctuation 7778 Pd Dash punctuation 7779 Pe Close punctuation 7780 Pf Final punctuation 7781 Pi Initial punctuation 7782 Po Other punctuation 7783 Ps Open punctuation 7784 7785 S Symbol 7786 Sc Currency symbol 7787 Sk Modifier symbol 7788 Sm Mathematical symbol 7789 So Other symbol 7790 7791 Z Separator 7792 Zl Line separator 7793 Zp Paragraph separator 7794 Zs Space separator 7795 7796 7797PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P 7798 7799 Xan Alphanumeric: union of properties L and N 7800 Xps POSIX space: property Z or tab, NL, VT, FF, CR 7801 Xsp Perl space: property Z or tab, NL, VT, FF, CR 7802 Xuc Univerally-named character: one that can be 7803 represented by a Universal Character Name 7804 Xwd Perl word: property Xan or underscore 7805 7806 Perl and POSIX space are now the same. Perl added VT to its space char- 7807 acter set at release 5.18 and PCRE changed at release 8.34. 7808 7809 7810SCRIPT NAMES FOR \p AND \P 7811 7812 Arabic, Armenian, Avestan, Balinese, Bamum, Bassa_Vah, Batak, Bengali, 7813 Bopomofo, Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Car- 7814 ian, Caucasian_Albanian, Chakma, Cham, Cherokee, Common, Coptic, Cunei- 7815 form, Cypriot, Cyrillic, Deseret, Devanagari, Duployan, Egyptian_Hiero- 7816 glyphs, Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha, 7817 Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, 7818 Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- 7819 tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, 7820 Kharoshthi, Khmer, Khojki, Khudawadi, Lao, Latin, Lepcha, Limbu, Lin- 7821 ear_A, Linear_B, Lisu, Lycian, Lydian, Mahajani, Malayalam, Mandaic, 7822 Manichaean, Meetei_Mayek, Mende_Kikakui, Meroitic_Cursive, 7823 Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro, Myanmar, Nabataean, 7824 New_Tai_Lue, Nko, Ogham, Ol_Chiki, Old_Italic, Old_North_Arabian, 7825 Old_Permic, Old_Persian, Old_South_Arabian, Old_Turkic, Oriya, Osmanya, 7826 Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, Phoenician, 7827 Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Sha- 7828 vian, Siddham, Sinhala, Sora_Sompeng, Sundanese, Syloti_Nagri, Syriac, 7829 Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, Takri, Tamil, Telugu, 7830 Thaana, Thai, Tibetan, Tifinagh, Tirhuta, Ugaritic, Vai, Warang_Citi, 7831 Yi. 7832 7833 7834CHARACTER CLASSES 7835 7836 [...] positive character class 7837 [^...] negative character class 7838 [x-y] range (can be used for hex characters) 7839 [[:xxx:]] positive POSIX named set 7840 [[:^xxx:]] negative POSIX named set 7841 7842 alnum alphanumeric 7843 alpha alphabetic 7844 ascii 0-127 7845 blank space or tab 7846 cntrl control character 7847 digit decimal digit 7848 graph printing, excluding space 7849 lower lower case letter 7850 print printing, including space 7851 punct printing, excluding alphanumeric 7852 space white space 7853 upper upper case letter 7854 word same as \w 7855 xdigit hexadecimal digit 7856 7857 In PCRE, POSIX character set names recognize only ASCII characters by 7858 default, but some of them use Unicode properties if PCRE_UCP is set. 7859 You can use \Q...\E inside a character class. 7860 7861 7862QUANTIFIERS 7863 7864 ? 0 or 1, greedy 7865 ?+ 0 or 1, possessive 7866 ?? 0 or 1, lazy 7867 * 0 or more, greedy 7868 *+ 0 or more, possessive 7869 *? 0 or more, lazy 7870 + 1 or more, greedy 7871 ++ 1 or more, possessive 7872 +? 1 or more, lazy 7873 {n} exactly n 7874 {n,m} at least n, no more than m, greedy 7875 {n,m}+ at least n, no more than m, possessive 7876 {n,m}? at least n, no more than m, lazy 7877 {n,} n or more, greedy 7878 {n,}+ n or more, possessive 7879 {n,}? n or more, lazy 7880 7881 7882ANCHORS AND SIMPLE ASSERTIONS 7883 7884 \b word boundary 7885 \B not a word boundary 7886 ^ start of subject 7887 also after internal newline in multiline mode 7888 \A start of subject 7889 $ end of subject 7890 also before newline at end of subject 7891 also before internal newline in multiline mode 7892 \Z end of subject 7893 also before newline at end of subject 7894 \z end of subject 7895 \G first matching position in subject 7896 7897 7898MATCH POINT RESET 7899 7900 \K reset start of match 7901 7902 \K is honoured in positive assertions, but ignored in negative ones. 7903 7904 7905ALTERNATION 7906 7907 expr|expr|expr... 7908 7909 7910CAPTURING 7911 7912 (...) capturing group 7913 (?<name>...) named capturing group (Perl) 7914 (?'name'...) named capturing group (Perl) 7915 (?P<name>...) named capturing group (Python) 7916 (?:...) non-capturing group 7917 (?|...) non-capturing group; reset group numbers for 7918 capturing groups in each alternative 7919 7920 7921ATOMIC GROUPS 7922 7923 (?>...) atomic, non-capturing group 7924 7925 7926COMMENT 7927 7928 (?#....) comment (not nestable) 7929 7930 7931OPTION SETTING 7932 7933 (?i) caseless 7934 (?J) allow duplicate names 7935 (?m) multiline 7936 (?s) single line (dotall) 7937 (?U) default ungreedy (lazy) 7938 (?x) extended (ignore white space) 7939 (?-...) unset option(s) 7940 7941 The following are recognized only at the very start of a pattern or 7942 after one of the newline or \R options with similar syntax. More than 7943 one of them may appear. 7944 7945 (*LIMIT_MATCH=d) set the match limit to d (decimal number) 7946 (*LIMIT_RECURSION=d) set the recursion limit to d (decimal number) 7947 (*NO_AUTO_POSSESS) no auto-possessification (PCRE_NO_AUTO_POSSESS) 7948 (*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE) 7949 (*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8) 7950 (*UTF16) set UTF-16 mode: 16-bit library (PCRE_UTF16) 7951 (*UTF32) set UTF-32 mode: 32-bit library (PCRE_UTF32) 7952 (*UTF) set appropriate UTF mode for the library in use 7953 (*UCP) set PCRE_UCP (use Unicode properties for \d etc) 7954 7955 Note that LIMIT_MATCH and LIMIT_RECURSION can only reduce the value of 7956 the limits set by the caller of pcre_exec(), not increase them. 7957 7958 7959NEWLINE CONVENTION 7960 7961 These are recognized only at the very start of the pattern or after 7962 option settings with a similar syntax. 7963 7964 (*CR) carriage return only 7965 (*LF) linefeed only 7966 (*CRLF) carriage return followed by linefeed 7967 (*ANYCRLF) all three of the above 7968 (*ANY) any Unicode newline sequence 7969 7970 7971WHAT \R MATCHES 7972 7973 These are recognized only at the very start of the pattern or after 7974 option setting with a similar syntax. 7975 7976 (*BSR_ANYCRLF) CR, LF, or CRLF 7977 (*BSR_UNICODE) any Unicode newline sequence 7978 7979 7980LOOKAHEAD AND LOOKBEHIND ASSERTIONS 7981 7982 (?=...) positive look ahead 7983 (?!...) negative look ahead 7984 (?<=...) positive look behind 7985 (?<!...) negative look behind 7986 7987 Each top-level branch of a look behind must be of a fixed length. 7988 7989 7990BACKREFERENCES 7991 7992 \n reference by number (can be ambiguous) 7993 \gn reference by number 7994 \g{n} reference by number 7995 \g{-n} relative reference by number 7996 \k<name> reference by name (Perl) 7997 \k'name' reference by name (Perl) 7998 \g{name} reference by name (Perl) 7999 \k{name} reference by name (.NET) 8000 (?P=name) reference by name (Python) 8001 8002 8003SUBROUTINE REFERENCES (POSSIBLY RECURSIVE) 8004 8005 (?R) recurse whole pattern 8006 (?n) call subpattern by absolute number 8007 (?+n) call subpattern by relative number 8008 (?-n) call subpattern by relative number 8009 (?&name) call subpattern by name (Perl) 8010 (?P>name) call subpattern by name (Python) 8011 \g<name> call subpattern by name (Oniguruma) 8012 \g'name' call subpattern by name (Oniguruma) 8013 \g<n> call subpattern by absolute number (Oniguruma) 8014 \g'n' call subpattern by absolute number (Oniguruma) 8015 \g<+n> call subpattern by relative number (PCRE extension) 8016 \g'+n' call subpattern by relative number (PCRE extension) 8017 \g<-n> call subpattern by relative number (PCRE extension) 8018 \g'-n' call subpattern by relative number (PCRE extension) 8019 8020 8021CONDITIONAL PATTERNS 8022 8023 (?(condition)yes-pattern) 8024 (?(condition)yes-pattern|no-pattern) 8025 8026 (?(n)... absolute reference condition 8027 (?(+n)... relative reference condition 8028 (?(-n)... relative reference condition 8029 (?(<name>)... named reference condition (Perl) 8030 (?('name')... named reference condition (Perl) 8031 (?(name)... named reference condition (PCRE) 8032 (?(R)... overall recursion condition 8033 (?(Rn)... specific group recursion condition 8034 (?(R&name)... specific recursion condition 8035 (?(DEFINE)... define subpattern for reference 8036 (?(assert)... assertion condition 8037 8038 8039BACKTRACKING CONTROL 8040 8041 The following act immediately they are reached: 8042 8043 (*ACCEPT) force successful match 8044 (*FAIL) force backtrack; synonym (*F) 8045 (*MARK:NAME) set name to be passed back; synonym (*:NAME) 8046 8047 The following act only when a subsequent match failure causes a back- 8048 track to reach them. They all force a match failure, but they differ in 8049 what happens afterwards. Those that advance the start-of-match point do 8050 so only if the pattern is not anchored. 8051 8052 (*COMMIT) overall failure, no advance of starting point 8053 (*PRUNE) advance to next starting character 8054 (*PRUNE:NAME) equivalent to (*MARK:NAME)(*PRUNE) 8055 (*SKIP) advance to current matching position 8056 (*SKIP:NAME) advance to position corresponding to an earlier 8057 (*MARK:NAME); if not found, the (*SKIP) is ignored 8058 (*THEN) local failure, backtrack to next alternation 8059 (*THEN:NAME) equivalent to (*MARK:NAME)(*THEN) 8060 8061 8062CALLOUTS 8063 8064 (?C) callout 8065 (?Cn) callout with data n 8066 8067 8068SEE ALSO 8069 8070 pcrepattern(3), pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3). 8071 8072 8073AUTHOR 8074 8075 Philip Hazel 8076 University Computing Service 8077 Cambridge CB2 3QH, England. 8078 8079 8080REVISION 8081 8082 Last updated: 08 January 2014 8083 Copyright (c) 1997-2014 University of Cambridge. 8084------------------------------------------------------------------------------ 8085 8086 8087PCREUNICODE(3) Library Functions Manual PCREUNICODE(3) 8088 8089 8090 8091NAME 8092 PCRE - Perl-compatible regular expressions 8093 8094UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT 8095 8096 As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) 8097 and UTF-32 (from release 8.32), by means of two additional libraries. 8098 They can be built as well as, or instead of, the 8-bit library. 8099 8100 8101UTF-8 SUPPORT 8102 8103 In order process UTF-8 strings, you must build PCRE's 8-bit library 8104 with UTF support, and, in addition, you must call pcre_compile() with 8105 the PCRE_UTF8 option flag, or the pattern must start with the sequence 8106 (*UTF8) or (*UTF). When either of these is the case, both the pattern 8107 and any subject strings that are matched against it are treated as 8108 UTF-8 strings instead of strings of individual 1-byte characters. 8109 8110 8111UTF-16 AND UTF-32 SUPPORT 8112 8113 In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit 8114 or 32-bit library with UTF support, and, in addition, you must call 8115 pcre16_compile() or pcre32_compile() with the PCRE_UTF16 or PCRE_UTF32 8116 option flag, as appropriate. Alternatively, the pattern must start with 8117 the sequence (*UTF16), (*UTF32), as appropriate, or (*UTF), which can 8118 be used with either library. When UTF mode is set, both the pattern and 8119 any subject strings that are matched against it are treated as UTF-16 8120 or UTF-32 strings instead of strings of individual 16-bit or 32-bit 8121 characters. 8122 8123 8124UTF SUPPORT OVERHEAD 8125 8126 If you compile PCRE with UTF support, but do not use it at run time, 8127 the library will be a bit bigger, but the additional run time overhead 8128 is limited to testing the PCRE_UTF[8|16|32] flag occasionally, so 8129 should not be very big. 8130 8131 8132UNICODE PROPERTY SUPPORT 8133 8134 If PCRE is built with Unicode character property support (which implies 8135 UTF support), the escape sequences \p{..}, \P{..}, and \X can be used. 8136 The available properties that can be tested are limited to the general 8137 category properties such as Lu for an upper case letter or Nd for a 8138 decimal number, the Unicode script names such as Arabic or Han, and the 8139 derived properties Any and L&. Full lists is given in the pcrepattern 8140 and pcresyntax documentation. Only the short names for properties are 8141 supported. For example, \p{L} matches a letter. Its Perl synonym, 8142 \p{Letter}, is not supported. Furthermore, in Perl, many properties 8143 may optionally be prefixed by "Is", for compatibility with Perl 5.6. 8144 PCRE does not support this. 8145 8146 Validity of UTF-8 strings 8147 8148 When you set the PCRE_UTF8 flag, the byte strings passed as patterns 8149 and subjects are (by default) checked for validity on entry to the rel- 8150 evant functions. The entire string is checked before any other process- 8151 ing takes place. From release 7.3 of PCRE, the check is according the 8152 rules of RFC 3629, which are themselves derived from the Unicode speci- 8153 fication. Earlier releases of PCRE followed the rules of RFC 2279, 8154 which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The 8155 current check allows only values in the range U+0 to U+10FFFF, exclud- 8156 ing the surrogate area. (From release 8.33 the so-called "non-charac- 8157 ter" code points are no longer excluded because Unicode corrigendum #9 8158 makes it clear that they should not be.) 8159 8160 Characters in the "Surrogate Area" of Unicode are reserved for use by 8161 UTF-16, where they are used in pairs to encode codepoints with values 8162 greater than 0xFFFF. The code points that are encoded by UTF-16 pairs 8163 are available independently in the UTF-8 and UTF-32 encodings. (In 8164 other words, the whole surrogate thing is a fudge for UTF-16 which 8165 unfortunately messes up UTF-8 and UTF-32.) 8166 8167 If an invalid UTF-8 string is passed to PCRE, an error return is given. 8168 At compile time, the only additional information is the offset to the 8169 first byte of the failing character. The run-time functions pcre_exec() 8170 and pcre_dfa_exec() also pass back this information, as well as a more 8171 detailed reason code if the caller has provided memory in which to do 8172 this. 8173 8174 In some situations, you may already know that your strings are valid, 8175 and therefore want to skip these checks in order to improve perfor- 8176 mance, for example in the case of a long subject string that is being 8177 scanned repeatedly. If you set the PCRE_NO_UTF8_CHECK flag at compile 8178 time or at run time, PCRE assumes that the pattern or subject it is 8179 given (respectively) contains only valid UTF-8 codes. In this case, it 8180 does not diagnose an invalid UTF-8 string. 8181 8182 Note that passing PCRE_NO_UTF8_CHECK to pcre_compile() just disables 8183 the check for the pattern; it does not also apply to subject strings. 8184 If you want to disable the check for a subject string you must pass 8185 this option to pcre_exec() or pcre_dfa_exec(). 8186 8187 If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the 8188 result is undefined and your program may crash. 8189 8190 Validity of UTF-16 strings 8191 8192 When you set the PCRE_UTF16 flag, the strings of 16-bit data units that 8193 are passed as patterns and subjects are (by default) checked for valid- 8194 ity on entry to the relevant functions. Values other than those in the 8195 surrogate range U+D800 to U+DFFF are independent code points. Values in 8196 the surrogate range must be used in pairs in the correct manner. 8197 8198 If an invalid UTF-16 string is passed to PCRE, an error return is 8199 given. At compile time, the only additional information is the offset 8200 to the first data unit of the failing character. The run-time functions 8201 pcre16_exec() and pcre16_dfa_exec() also pass back this information, as 8202 well as a more detailed reason code if the caller has provided memory 8203 in which to do this. 8204 8205 In some situations, you may already know that your strings are valid, 8206 and therefore want to skip these checks in order to improve perfor- 8207 mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at 8208 run time, PCRE assumes that the pattern or subject it is given (respec- 8209 tively) contains only valid UTF-16 sequences. In this case, it does not 8210 diagnose an invalid UTF-16 string. However, if an invalid string is 8211 passed, the result is undefined. 8212 8213 Validity of UTF-32 strings 8214 8215 When you set the PCRE_UTF32 flag, the strings of 32-bit data units that 8216 are passed as patterns and subjects are (by default) checked for valid- 8217 ity on entry to the relevant functions. This check allows only values 8218 in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to 8219 U+DFFF. 8220 8221 If an invalid UTF-32 string is passed to PCRE, an error return is 8222 given. At compile time, the only additional information is the offset 8223 to the first data unit of the failing character. The run-time functions 8224 pcre32_exec() and pcre32_dfa_exec() also pass back this information, as 8225 well as a more detailed reason code if the caller has provided memory 8226 in which to do this. 8227 8228 In some situations, you may already know that your strings are valid, 8229 and therefore want to skip these checks in order to improve perfor- 8230 mance. If you set the PCRE_NO_UTF32_CHECK flag at compile time or at 8231 run time, PCRE assumes that the pattern or subject it is given (respec- 8232 tively) contains only valid UTF-32 sequences. In this case, it does not 8233 diagnose an invalid UTF-32 string. However, if an invalid string is 8234 passed, the result is undefined. 8235 8236 General comments about UTF modes 8237 8238 1. Codepoints less than 256 can be specified in patterns by either 8239 braced or unbraced hexadecimal escape sequences (for example, \x{b3} or 8240 \xb3). Larger values have to use braced sequences. 8241 8242 2. Octal numbers up to \777 are recognized, and in UTF-8 mode they 8243 match two-byte characters for values greater than \177. 8244 8245 3. Repeat quantifiers apply to complete UTF characters, not to individ- 8246 ual data units, for example: \x{100}{3}. 8247 8248 4. The dot metacharacter matches one UTF character instead of a single 8249 data unit. 8250 8251 5. The escape sequence \C can be used to match a single byte in UTF-8 8252 mode, or a single 16-bit data unit in UTF-16 mode, or a single 32-bit 8253 data unit in UTF-32 mode, but its use can lead to some strange effects 8254 because it breaks up multi-unit characters (see the description of \C 8255 in the pcrepattern documentation). The use of \C is not supported in 8256 the alternative matching function pcre[16|32]_dfa_exec(), nor is it 8257 supported in UTF mode by the JIT optimization of pcre[16|32]_exec(). If 8258 JIT optimization is requested for a UTF pattern that contains \C, it 8259 will not succeed, and so the matching will be carried out by the normal 8260 interpretive function. 8261 8262 6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly 8263 test characters of any code value, but, by default, the characters that 8264 PCRE recognizes as digits, spaces, or word characters remain the same 8265 set as in non-UTF mode, all with values less than 256. This remains 8266 true even when PCRE is built to include Unicode property support, 8267 because to do otherwise would slow down PCRE in many common cases. Note 8268 in particular that this applies to \b and \B, because they are defined 8269 in terms of \w and \W. If you really want to test for a wider sense of, 8270 say, "digit", you can use explicit Unicode property tests such as 8271 \p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the 8272 character escapes work is changed so that Unicode properties are used 8273 to determine which characters match. There are more details in the sec- 8274 tion on generic character types in the pcrepattern documentation. 8275 8276 7. Similarly, characters that match the POSIX named character classes 8277 are all low-valued characters, unless the PCRE_UCP option is set. 8278 8279 8. However, the horizontal and vertical white space matching escapes 8280 (\h, \H, \v, and \V) do match all the appropriate Unicode characters, 8281 whether or not PCRE_UCP is set. 8282 8283 9. Case-insensitive matching applies only to characters whose values 8284 are less than 128, unless PCRE is built with Unicode property support. 8285 A few Unicode characters such as Greek sigma have more than two code- 8286 points that are case-equivalent. Up to and including PCRE release 8.31, 8287 only one-to-one case mappings were supported, but later releases (with 8288 Unicode property support) do treat as case-equivalent all versions of 8289 characters such as Greek sigma. 8290 8291 8292AUTHOR 8293 8294 Philip Hazel 8295 University Computing Service 8296 Cambridge CB2 3QH, England. 8297 8298 8299REVISION 8300 8301 Last updated: 27 February 2013 8302 Copyright (c) 1997-2013 University of Cambridge. 8303------------------------------------------------------------------------------ 8304 8305 8306PCREJIT(3) Library Functions Manual PCREJIT(3) 8307 8308 8309 8310NAME 8311 PCRE - Perl-compatible regular expressions 8312 8313PCRE JUST-IN-TIME COMPILER SUPPORT 8314 8315 Just-in-time compiling is a heavyweight optimization that can greatly 8316 speed up pattern matching. However, it comes at the cost of extra pro- 8317 cessing before the match is performed. Therefore, it is of most benefit 8318 when the same pattern is going to be matched many times. This does not 8319 necessarily mean many calls of a matching function; if the pattern is 8320 not anchored, matching attempts may take place many times at various 8321 positions in the subject, even for a single call. Therefore, if the 8322 subject string is very long, it may still pay to use JIT for one-off 8323 matches. 8324 8325 JIT support applies only to the traditional Perl-compatible matching 8326 function. It does not apply when the DFA matching function is being 8327 used. The code for this support was written by Zoltan Herczeg. 8328 8329 83308-BIT, 16-BIT AND 32-BIT SUPPORT 8331 8332 JIT support is available for all of the 8-bit, 16-bit and 32-bit PCRE 8333 libraries. To keep this documentation simple, only the 8-bit interface 8334 is described in what follows. If you are using the 16-bit library, sub- 8335 stitute the 16-bit functions and 16-bit structures (for example, 8336 pcre16_jit_stack instead of pcre_jit_stack). If you are using the 8337 32-bit library, substitute the 32-bit functions and 32-bit structures 8338 (for example, pcre32_jit_stack instead of pcre_jit_stack). 8339 8340 8341AVAILABILITY OF JIT SUPPORT 8342 8343 JIT support is an optional feature of PCRE. The "configure" option 8344 --enable-jit (or equivalent CMake option) must be set when PCRE is 8345 built if you want to use JIT. The support is limited to the following 8346 hardware platforms: 8347 8348 ARM v5, v7, and Thumb2 8349 Intel x86 32-bit and 64-bit 8350 MIPS 32-bit 8351 Power PC 32-bit and 64-bit 8352 SPARC 32-bit (experimental) 8353 8354 If --enable-jit is set on an unsupported platform, compilation fails. 8355 8356 A program that is linked with PCRE 8.20 or later can tell if JIT sup- 8357 port is available by calling pcre_config() with the PCRE_CONFIG_JIT 8358 option. The result is 1 when JIT is available, and 0 otherwise. How- 8359 ever, a simple program does not need to check this in order to use JIT. 8360 The normal API is implemented in a way that falls back to the interpre- 8361 tive code if JIT is not available. For programs that need the best pos- 8362 sible performance, there is also a "fast path" API that is JIT-spe- 8363 cific. 8364 8365 If your program may sometimes be linked with versions of PCRE that are 8366 older than 8.20, but you want to use JIT when it is available, you can 8367 test the values of PCRE_MAJOR and PCRE_MINOR, or the existence of a JIT 8368 macro such as PCRE_CONFIG_JIT, for compile-time control of your code. 8369 Also beware that the pcre_jit_exec() function was not available at all 8370 before 8.32, and may not be available at all if PCRE isn't compiled 8371 with --enable-jit. See the "JIT FAST PATH API" section below for 8372 details. 8373 8374 8375SIMPLE USE OF JIT 8376 8377 You have to do two things to make use of the JIT support in the sim- 8378 plest way: 8379 8380 (1) Call pcre_study() with the PCRE_STUDY_JIT_COMPILE option for 8381 each compiled pattern, and pass the resulting pcre_extra block to 8382 pcre_exec(). 8383 8384 (2) Use pcre_free_study() to free the pcre_extra block when it is 8385 no longer needed, instead of just freeing it yourself. This 8386 ensures that 8387 any JIT data is also freed. 8388 8389 For a program that may be linked with pre-8.20 versions of PCRE, you 8390 can insert 8391 8392 #ifndef PCRE_STUDY_JIT_COMPILE 8393 #define PCRE_STUDY_JIT_COMPILE 0 8394 #endif 8395 8396 so that no option is passed to pcre_study(), and then use something 8397 like this to free the study data: 8398 8399 #ifdef PCRE_CONFIG_JIT 8400 pcre_free_study(study_ptr); 8401 #else 8402 pcre_free(study_ptr); 8403 #endif 8404 8405 PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for 8406 complete matches. If you want to run partial matches using the 8407 PCRE_PARTIAL_HARD or PCRE_PARTIAL_SOFT options of pcre_exec(), you 8408 should set one or both of the following options in addition to, or 8409 instead of, PCRE_STUDY_JIT_COMPILE when you call pcre_study(): 8410 8411 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE 8412 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE 8413 8414 If using pcre_jit_exec() and supporting a pre-8.32 version of PCRE, you 8415 can insert: 8416 8417 #if PCRE_MAJOR >= 8 && PCRE_MINOR >= 32 8418 pcre_jit_exec(...); 8419 #else 8420 pcre_exec(...) 8421 #endif 8422 8423 but as described in the "JIT FAST PATH API" section below this assumes 8424 version 8.32 and later are compiled with --enable-jit, which may break. 8425 8426 The JIT compiler generates different optimized code for each of the 8427 three modes (normal, soft partial, hard partial). When pcre_exec() is 8428 called, the appropriate code is run if it is available. Otherwise, the 8429 pattern is matched using interpretive code. 8430 8431 In some circumstances you may need to call additional functions. These 8432 are described in the section entitled "Controlling the JIT stack" 8433 below. 8434 8435 If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are 8436 ignored, and no JIT data is created. Otherwise, the compiled pattern is 8437 passed to the JIT compiler, which turns it into machine code that exe- 8438 cutes much faster than the normal interpretive code. When pcre_exec() 8439 is passed a pcre_extra block containing a pointer to JIT code of the 8440 appropriate mode (normal or hard/soft partial), it obeys that code 8441 instead of running the interpreter. The result is identical, but the 8442 compiled JIT code runs much faster. 8443 8444 There are some pcre_exec() options that are not supported for JIT exe- 8445 cution. There are also some pattern items that JIT cannot handle. 8446 Details are given below. In both cases, execution automatically falls 8447 back to the interpretive code. If you want to know whether JIT was 8448 actually used for a particular match, you should arrange for a JIT 8449 callback function to be set up as described in the section entitled 8450 "Controlling the JIT stack" below, even if you do not need to supply a 8451 non-default JIT stack. Such a callback function is called whenever JIT 8452 code is about to be obeyed. If the execution options are not right for 8453 JIT execution, the callback function is not obeyed. 8454 8455 If the JIT compiler finds an unsupported item, no JIT data is gener- 8456 ated. You can find out if JIT execution is available after studying a 8457 pattern by calling pcre_fullinfo() with the PCRE_INFO_JIT option. A 8458 result of 1 means that JIT compilation was successful. A result of 0 8459 means that JIT support is not available, or the pattern was not studied 8460 with PCRE_STUDY_JIT_COMPILE etc., or the JIT compiler was not able to 8461 handle the pattern. 8462 8463 Once a pattern has been studied, with or without JIT, it can be used as 8464 many times as you like for matching different subject strings. 8465 8466 8467UNSUPPORTED OPTIONS AND PATTERN ITEMS 8468 8469 The only pcre_exec() options that are supported for JIT execution are 8470 PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NO_UTF32_CHECK, PCRE_NOT- 8471 BOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PAR- 8472 TIAL_HARD, and PCRE_PARTIAL_SOFT. 8473 8474 The only unsupported pattern items are \C (match a single data unit) 8475 when running in a UTF mode, and a callout immediately before an asser- 8476 tion condition in a conditional group. 8477 8478 8479RETURN VALUES FROM JIT EXECUTION 8480 8481 When a pattern is matched using JIT execution, the return values are 8482 the same as those given by the interpretive pcre_exec() code, with the 8483 addition of one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means 8484 that the memory used for the JIT stack was insufficient. See "Control- 8485 ling the JIT stack" below for a discussion of JIT stack usage. For com- 8486 patibility with the interpretive pcre_exec() code, no more than two- 8487 thirds of the ovector argument is used for passing back captured sub- 8488 strings. 8489 8490 The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if 8491 searching a very large pattern tree goes on for too long, as it is in 8492 the same circumstance when JIT is not used, but the details of exactly 8493 what is counted are not the same. The PCRE_ERROR_RECURSIONLIMIT error 8494 code is never returned by JIT execution. 8495 8496 8497SAVING AND RESTORING COMPILED PATTERNS 8498 8499 The code that is generated by the JIT compiler is architecture-spe- 8500 cific, and is also position dependent. For those reasons it cannot be 8501 saved (in a file or database) and restored later like the bytecode and 8502 other data of a compiled pattern. Saving and restoring compiled pat- 8503 terns is not something many people do. More detail about this facility 8504 is given in the pcreprecompile documentation. It should be possible to 8505 run pcre_study() on a saved and restored pattern, and thereby recreate 8506 the JIT data, but because JIT compilation uses significant resources, 8507 it is probably not worth doing this; you might as well recompile the 8508 original pattern. 8509 8510 8511CONTROLLING THE JIT STACK 8512 8513 When the compiled JIT code runs, it needs a block of memory to use as a 8514 stack. By default, it uses 32K on the machine stack. However, some 8515 large or complicated patterns need more than this. The error 8516 PCRE_ERROR_JIT_STACKLIMIT is given when there is not enough stack. 8517 Three functions are provided for managing blocks of memory for use as 8518 JIT stacks. There is further discussion about the use of JIT stacks in 8519 the section entitled "JIT stack FAQ" below. 8520 8521 The pcre_jit_stack_alloc() function creates a JIT stack. Its arguments 8522 are a starting size and a maximum size, and it returns a pointer to an 8523 opaque structure of type pcre_jit_stack, or NULL if there is an error. 8524 The pcre_jit_stack_free() function can be used to free a stack that is 8525 no longer needed. (For the technically minded: the address space is 8526 allocated by mmap or VirtualAlloc.) 8527 8528 JIT uses far less memory for recursion than the interpretive code, and 8529 a maximum stack size of 512K to 1M should be more than enough for any 8530 pattern. 8531 8532 The pcre_assign_jit_stack() function specifies which stack JIT code 8533 should use. Its arguments are as follows: 8534 8535 pcre_extra *extra 8536 pcre_jit_callback callback 8537 void *data 8538 8539 The extra argument must be the result of studying a pattern with 8540 PCRE_STUDY_JIT_COMPILE etc. There are three cases for the values of the 8541 other two options: 8542 8543 (1) If callback is NULL and data is NULL, an internal 32K block 8544 on the machine stack is used. 8545 8546 (2) If callback is NULL and data is not NULL, data must be 8547 a valid JIT stack, the result of calling pcre_jit_stack_alloc(). 8548 8549 (3) If callback is not NULL, it must point to a function that is 8550 called with data as an argument at the start of matching, in 8551 order to set up a JIT stack. If the return from the callback 8552 function is NULL, the internal 32K stack is used; otherwise the 8553 return value must be a valid JIT stack, the result of calling 8554 pcre_jit_stack_alloc(). 8555 8556 A callback function is obeyed whenever JIT code is about to be run; it 8557 is not obeyed when pcre_exec() is called with options that are incom- 8558 patible for JIT execution. A callback function can therefore be used to 8559 determine whether a match operation was executed by JIT or by the 8560 interpreter. 8561 8562 You may safely use the same JIT stack for more than one pattern (either 8563 by assigning directly or by callback), as long as the patterns are all 8564 matched sequentially in the same thread. In a multithread application, 8565 if you do not specify a JIT stack, or if you assign or pass back NULL 8566 from a callback, that is thread-safe, because each thread has its own 8567 machine stack. However, if you assign or pass back a non-NULL JIT 8568 stack, this must be a different stack for each thread so that the 8569 application is thread-safe. 8570 8571 Strictly speaking, even more is allowed. You can assign the same non- 8572 NULL stack to any number of patterns as long as they are not used for 8573 matching by multiple threads at the same time. For example, you can 8574 assign the same stack to all compiled patterns, and use a global mutex 8575 in the callback to wait until the stack is available for use. However, 8576 this is an inefficient solution, and not recommended. 8577 8578 This is a suggestion for how a multithreaded program that needs to set 8579 up non-default JIT stacks might operate: 8580 8581 During thread initalization 8582 thread_local_var = pcre_jit_stack_alloc(...) 8583 8584 During thread exit 8585 pcre_jit_stack_free(thread_local_var) 8586 8587 Use a one-line callback function 8588 return thread_local_var 8589 8590 All the functions described in this section do nothing if JIT is not 8591 available, and pcre_assign_jit_stack() does nothing unless the extra 8592 argument is non-NULL and points to a pcre_extra block that is the 8593 result of a successful study with PCRE_STUDY_JIT_COMPILE etc. 8594 8595 8596JIT STACK FAQ 8597 8598 (1) Why do we need JIT stacks? 8599 8600 PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack 8601 where the local data of the current node is pushed before checking its 8602 child nodes. Allocating real machine stack on some platforms is diffi- 8603 cult. For example, the stack chain needs to be updated every time if we 8604 extend the stack on PowerPC. Although it is possible, its updating 8605 time overhead decreases performance. So we do the recursion in memory. 8606 8607 (2) Why don't we simply allocate blocks of memory with malloc()? 8608 8609 Modern operating systems have a nice feature: they can reserve an 8610 address space instead of allocating memory. We can safely allocate mem- 8611 ory pages inside this address space, so the stack could grow without 8612 moving memory data (this is important because of pointers). Thus we can 8613 allocate 1M address space, and use only a single memory page (usually 8614 4K) if that is enough. However, we can still grow up to 1M anytime if 8615 needed. 8616 8617 (3) Who "owns" a JIT stack? 8618 8619 The owner of the stack is the user program, not the JIT studied pattern 8620 or anything else. The user program must ensure that if a stack is used 8621 by pcre_exec(), (that is, it is assigned to the pattern currently run- 8622 ning), that stack must not be used by any other threads (to avoid over- 8623 writing the same memory area). The best practice for multithreaded pro- 8624 grams is to allocate a stack for each thread, and return this stack 8625 through the JIT callback function. 8626 8627 (4) When should a JIT stack be freed? 8628 8629 You can free a JIT stack at any time, as long as it will not be used by 8630 pcre_exec() again. When you assign the stack to a pattern, only a 8631 pointer is set. There is no reference counting or any other magic. You 8632 can free the patterns and stacks in any order, anytime. Just do not 8633 call pcre_exec() with a pattern pointing to an already freed stack, as 8634 that will cause SEGFAULT. (Also, do not free a stack currently used by 8635 pcre_exec() in another thread). You can also replace the stack for a 8636 pattern at any time. You can even free the previous stack before 8637 assigning a replacement. 8638 8639 (5) Should I allocate/free a stack every time before/after calling 8640 pcre_exec()? 8641 8642 No, because this is too costly in terms of resources. However, you 8643 could implement some clever idea which release the stack if it is not 8644 used in let's say two minutes. The JIT callback can help to achieve 8645 this without keeping a list of the currently JIT studied patterns. 8646 8647 (6) OK, the stack is for long term memory allocation. But what happens 8648 if a pattern causes stack overflow with a stack of 1M? Is that 1M kept 8649 until the stack is freed? 8650 8651 Especially on embedded sytems, it might be a good idea to release mem- 8652 ory sometimes without freeing the stack. There is no API for this at 8653 the moment. Probably a function call which returns with the currently 8654 allocated memory for any stack and another which allows releasing mem- 8655 ory (shrinking the stack) would be a good idea if someone needs this. 8656 8657 (7) This is too much of a headache. Isn't there any better solution for 8658 JIT stack handling? 8659 8660 No, thanks to Windows. If POSIX threads were used everywhere, we could 8661 throw out this complicated API. 8662 8663 8664EXAMPLE CODE 8665 8666 This is a single-threaded example that specifies a JIT stack without 8667 using a callback. 8668 8669 int rc; 8670 int ovector[30]; 8671 pcre *re; 8672 pcre_extra *extra; 8673 pcre_jit_stack *jit_stack; 8674 8675 re = pcre_compile(pattern, 0, &error, &erroffset, NULL); 8676 /* Check for errors */ 8677 extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error); 8678 jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024); 8679 /* Check for error (NULL) */ 8680 pcre_assign_jit_stack(extra, NULL, jit_stack); 8681 rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30); 8682 /* Check results */ 8683 pcre_free(re); 8684 pcre_free_study(extra); 8685 pcre_jit_stack_free(jit_stack); 8686 8687 8688JIT FAST PATH API 8689 8690 Because the API described above falls back to interpreted execution 8691 when JIT is not available, it is convenient for programs that are writ- 8692 ten for general use in many environments. However, calling JIT via 8693 pcre_exec() does have a performance impact. Programs that are written 8694 for use where JIT is known to be available, and which need the best 8695 possible performance, can instead use a "fast path" API to call JIT 8696 execution directly instead of calling pcre_exec() (obviously only for 8697 patterns that have been successfully studied by JIT). 8698 8699 The fast path function is called pcre_jit_exec(), and it takes exactly 8700 the same arguments as pcre_exec(), plus one additional argument that 8701 must point to a JIT stack. The JIT stack arrangements described above 8702 do not apply. The return values are the same as for pcre_exec(). 8703 8704 When you call pcre_exec(), as well as testing for invalid options, a 8705 number of other sanity checks are performed on the arguments. For exam- 8706 ple, if the subject pointer is NULL, or its length is negative, an 8707 immediate error is given. Also, unless PCRE_NO_UTF[8|16|32] is set, a 8708 UTF subject string is tested for validity. In the interests of speed, 8709 these checks do not happen on the JIT fast path, and if invalid data is 8710 passed, the result is undefined. 8711 8712 Bypassing the sanity checks and the pcre_exec() wrapping can give 8713 speedups of more than 10%. 8714 8715 Note that the pcre_jit_exec() function is not available in versions of 8716 PCRE before 8.32 (released in November 2012). If you need to support 8717 versions that old you must either use the slower pcre_exec(), or switch 8718 between the two codepaths by checking the values of PCRE_MAJOR and 8719 PCRE_MINOR. 8720 8721 Due to an unfortunate implementation oversight, even in versions 8.32 8722 and later there will be no pcre_jit_exec() stub function defined when 8723 PCRE is compiled with --disable-jit, which is the default, and there's 8724 no way to detect whether PCRE was compiled with --enable-jit via a 8725 macro. 8726 8727 If you need to support versions older than 8.32, or versions that may 8728 not build with --enable-jit, you must either use the slower 8729 pcre_exec(), or switch between the two codepaths by checking the values 8730 of PCRE_MAJOR and PCRE_MINOR. 8731 8732 Switching between the two by checking the version assumes that all the 8733 versions being targeted are built with --enable-jit. To also support 8734 builds that may use --disable-jit either pcre_exec() must be used, or a 8735 compile-time check for JIT via pcre_config() (which assumes the runtime 8736 environment will be the same), or as the Git project decided to do, 8737 simply assume that pcre_jit_exec() is present in 8.32 or later unless a 8738 compile-time flag is provided, see the "grep: un-break building with 8739 PCRE >= 8.32 without --enable-jit" commit in git.git for an example of 8740 that. 8741 8742 8743SEE ALSO 8744 8745 pcreapi(3) 8746 8747 8748AUTHOR 8749 8750 Philip Hazel (FAQ by Zoltan Herczeg) 8751 University Computing Service 8752 Cambridge CB2 3QH, England. 8753 8754 8755REVISION 8756 8757 Last updated: 05 July 2017 8758 Copyright (c) 1997-2017 University of Cambridge. 8759------------------------------------------------------------------------------ 8760 8761 8762PCREPARTIAL(3) Library Functions Manual PCREPARTIAL(3) 8763 8764 8765 8766NAME 8767 PCRE - Perl-compatible regular expressions 8768 8769PARTIAL MATCHING IN PCRE 8770 8771 In normal use of PCRE, if the subject string that is passed to a match- 8772 ing function matches as far as it goes, but is too short to match the 8773 entire pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances 8774 where it might be helpful to distinguish this case from other cases in 8775 which there is no match. 8776 8777 Consider, for example, an application where a human is required to type 8778 in data for a field with specific formatting requirements. An example 8779 might be a date in the form ddmmmyy, defined by this pattern: 8780 8781 ^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$ 8782 8783 If the application sees the user's keystrokes one by one, and can check 8784 that what has been typed so far is potentially valid, it is able to 8785 raise an error as soon as a mistake is made, by beeping and not 8786 reflecting the character that has been typed, for example. This immedi- 8787 ate feedback is likely to be a better user interface than a check that 8788 is delayed until the entire string has been entered. Partial matching 8789 can also be useful when the subject string is very long and is not all 8790 available at once. 8791 8792 PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and 8793 PCRE_PARTIAL_HARD options, which can be set when calling any of the 8794 matching functions. For backwards compatibility, PCRE_PARTIAL is a syn- 8795 onym for PCRE_PARTIAL_SOFT. The essential difference between the two 8796 options is whether or not a partial match is preferred to an alterna- 8797 tive complete match, though the details differ between the two types of 8798 matching function. If both options are set, PCRE_PARTIAL_HARD takes 8799 precedence. 8800 8801 If you want to use partial matching with just-in-time optimized code, 8802 you must call pcre_study(), pcre16_study() or pcre32_study() with one 8803 or both of these options: 8804 8805 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE 8806 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE 8807 8808 PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non- 8809 partial matches on the same pattern. If the appropriate JIT study mode 8810 has not been set for a match, the interpretive matching code is used. 8811 8812 Setting a partial matching option disables two of PCRE's standard opti- 8813 mizations. PCRE remembers the last literal data unit in a pattern, and 8814 abandons matching immediately if it is not present in the subject 8815 string. This optimization cannot be used for a subject string that 8816 might match only partially. If the pattern was studied, PCRE knows the 8817 minimum length of a matching string, and does not bother to run the 8818 matching function on shorter strings. This optimization is also dis- 8819 abled for partial matching. 8820 8821 8822PARTIAL MATCHING USING pcre_exec() OR pcre[16|32]_exec() 8823 8824 A partial match occurs during a call to pcre_exec() or 8825 pcre[16|32]_exec() when the end of the subject string is reached suc- 8826 cessfully, but matching cannot continue because more characters are 8827 needed. However, at least one character in the subject must have been 8828 inspected. This character need not form part of the final matched 8829 string; lookbehind assertions and the \K escape sequence provide ways 8830 of inspecting characters before the start of a matched substring. The 8831 requirement for inspecting at least one character exists because an 8832 empty string can always be matched; without such a restriction there 8833 would always be a partial match of an empty string at the end of the 8834 subject. 8835 8836 If there are at least two slots in the offsets vector when a partial 8837 match is returned, the first slot is set to the offset of the earliest 8838 character that was inspected. For convenience, the second offset points 8839 to the end of the subject so that a substring can easily be identified. 8840 If there are at least three slots in the offsets vector, the third slot 8841 is set to the offset of the character where matching started. 8842 8843 For the majority of patterns, the contents of the first and third slots 8844 will be the same. However, for patterns that contain lookbehind asser- 8845 tions, or begin with \b or \B, characters before the one where matching 8846 started may have been inspected while carrying out the match. For exam- 8847 ple, consider this pattern: 8848 8849 /(?<=abc)123/ 8850 8851 This pattern matches "123", but only if it is preceded by "abc". If the 8852 subject string is "xyzabc12", the first two offsets after a partial 8853 match are for the substring "abc12", because all these characters were 8854 inspected. However, the third offset is set to 6, because that is the 8855 offset where matching began. 8856 8857 What happens when a partial match is identified depends on which of the 8858 two partial matching options are set. 8859 8860 PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre[16|32]_exec() 8861 8862 If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre[16|32]_exec() 8863 identifies a partial match, the partial match is remembered, but match- 8864 ing continues as normal, and other alternatives in the pattern are 8865 tried. If no complete match can be found, PCRE_ERROR_PARTIAL is 8866 returned instead of PCRE_ERROR_NOMATCH. 8867 8868 This option is "soft" because it prefers a complete match over a par- 8869 tial match. All the various matching items in a pattern behave as if 8870 the subject string is potentially complete. For example, \z, \Z, and $ 8871 match at the end of the subject, as normal, and for \b and \B the end 8872 of the subject is treated as a non-alphanumeric. 8873 8874 If there is more than one partial match, the first one that was found 8875 provides the data that is returned. Consider this pattern: 8876 8877 /123\w+X|dogY/ 8878 8879 If this is matched against the subject string "abc123dog", both alter- 8880 natives fail to match, but the end of the subject is reached during 8881 matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 8882 and 9, identifying "123dog" as the first partial match that was found. 8883 (In this example, there are two partial matches, because "dog" on its 8884 own partially matches the second alternative.) 8885 8886 PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre[16|32]_exec() 8887 8888 If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre[16|32]_exec(), 8889 PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, 8890 without continuing to search for possible complete matches. This option 8891 is "hard" because it prefers an earlier partial match over a later com- 8892 plete match. For this reason, the assumption is made that the end of 8893 the supplied subject string may not be the true end of the available 8894 data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the 8895 subject, the result is PCRE_ERROR_PARTIAL, provided that at least one 8896 character in the subject has been inspected. 8897 8898 Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject 8899 strings are checked for validity. Normally, an invalid sequence causes 8900 the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the 8901 special case of a truncated character at the end of the subject, 8902 PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when 8903 PCRE_PARTIAL_HARD is set. 8904 8905 Comparing hard and soft partial matching 8906 8907 The difference between the two partial matching options can be illus- 8908 trated by a pattern such as: 8909 8910 /dog(sbody)?/ 8911 8912 This matches either "dog" or "dogsbody", greedily (that is, it prefers 8913 the longer string if possible). If it is matched against the string 8914 "dog" with PCRE_PARTIAL_SOFT, it yields a complete match for "dog". 8915 However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL. 8916 On the other hand, if the pattern is made ungreedy the result is dif- 8917 ferent: 8918 8919 /dog(sbody)??/ 8920 8921 In this case the result is always a complete match because that is 8922 found first, and matching never continues after finding a complete 8923 match. It might be easier to follow this explanation by thinking of the 8924 two patterns like this: 8925 8926 /dog(sbody)?/ is the same as /dogsbody|dog/ 8927 /dog(sbody)??/ is the same as /dog|dogsbody/ 8928 8929 The second pattern will never match "dogsbody", because it will always 8930 find the shorter match first. 8931 8932 8933PARTIAL MATCHING USING pcre_dfa_exec() OR pcre[16|32]_dfa_exec() 8934 8935 The DFA functions move along the subject string character by character, 8936 without backtracking, searching for all possible matches simultane- 8937 ously. If the end of the subject is reached before the end of the pat- 8938 tern, there is the possibility of a partial match, again provided that 8939 at least one character has been inspected. 8940 8941 When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if 8942 there have been no complete matches. Otherwise, the complete matches 8943 are returned. However, if PCRE_PARTIAL_HARD is set, a partial match 8944 takes precedence over any complete matches. The portion of the string 8945 that was inspected when the longest partial match was found is set as 8946 the first matching string, provided there are at least two slots in the 8947 offsets vector. 8948 8949 Because the DFA functions always search for all possible matches, and 8950 there is no difference between greedy and ungreedy repetition, their 8951 behaviour is different from the standard functions when PCRE_PAR- 8952 TIAL_HARD is set. Consider the string "dog" matched against the 8953 ungreedy pattern shown above: 8954 8955 /dog(sbody)??/ 8956 8957 Whereas the standard functions stop as soon as they find the complete 8958 match for "dog", the DFA functions also find the partial match for 8959 "dogsbody", and so return that when PCRE_PARTIAL_HARD is set. 8960 8961 8962PARTIAL MATCHING AND WORD BOUNDARIES 8963 8964 If a pattern ends with one of sequences \b or \B, which test for word 8965 boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter- 8966 intuitive results. Consider this pattern: 8967 8968 /\bcat\b/ 8969 8970 This matches "cat", provided there is a word boundary at either end. If 8971 the subject string is "the cat", the comparison of the final "t" with a 8972 following character cannot take place, so a partial match is found. 8973 However, normal matching carries on, and \b matches at the end of the 8974 subject when the last character is a letter, so a complete match is 8975 found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using 8976 PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because 8977 then the partial match takes precedence. 8978 8979 8980FORMERLY RESTRICTED PATTERNS 8981 8982 For releases of PCRE prior to 8.00, because of the way certain internal 8983 optimizations were implemented in the pcre_exec() function, the 8984 PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be 8985 used with all patterns. From release 8.00 onwards, the restrictions no 8986 longer apply, and partial matching with can be requested for any pat- 8987 tern. 8988 8989 Items that were formerly restricted were repeated single characters and 8990 repeated metasequences. If PCRE_PARTIAL was set for a pattern that did 8991 not conform to the restrictions, pcre_exec() returned the error code 8992 PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The 8993 PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled 8994 pattern can be used for partial matching now always returns 1. 8995 8996 8997EXAMPLE OF PARTIAL MATCHING USING PCRETEST 8998 8999 If the escape sequence \P is present in a pcretest data line, the 9000 PCRE_PARTIAL_SOFT option is used for the match. Here is a run of 9001 pcretest that uses the date example quoted above: 9002 9003 re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ 9004 data> 25jun04\P 9005 0: 25jun04 9006 1: jun 9007 data> 25dec3\P 9008 Partial match: 23dec3 9009 data> 3ju\P 9010 Partial match: 3ju 9011 data> 3juj\P 9012 No match 9013 data> j\P 9014 No match 9015 9016 The first data string is matched completely, so pcretest shows the 9017 matched substrings. The remaining four strings do not match the com- 9018 plete pattern, but the first two are partial matches. Similar output is 9019 obtained if DFA matching is used. 9020 9021 If the escape sequence \P is present more than once in a pcretest data 9022 line, the PCRE_PARTIAL_HARD option is set for the match. 9023 9024 9025MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre[16|32]_dfa_exec() 9026 9027 When a partial match has been found using a DFA matching function, it 9028 is possible to continue the match by providing additional subject data 9029 and calling the function again with the same compiled regular expres- 9030 sion, this time setting the PCRE_DFA_RESTART option. You must pass the 9031 same working space as before, because this is where details of the pre- 9032 vious partial match are stored. Here is an example using pcretest, 9033 using the \R escape sequence to set the PCRE_DFA_RESTART option (\D 9034 specifies the use of the DFA matching function): 9035 9036 re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ 9037 data> 23ja\P\D 9038 Partial match: 23ja 9039 data> n05\R\D 9040 0: n05 9041 9042 The first call has "23ja" as the subject, and requests partial match- 9043 ing; the second call has "n05" as the subject for the continued 9044 (restarted) match. Notice that when the match is complete, only the 9045 last part is shown; PCRE does not retain the previously partially- 9046 matched string. It is up to the calling program to do that if it needs 9047 to. 9048 9049 That means that, for an unanchored pattern, if a continued match fails, 9050 it is not possible to try again at a new starting point. All this 9051 facility is capable of doing is continuing with the previous match 9052 attempt. In the previous example, if the second set of data is "ug23" 9053 the result is no match, even though there would be a match for "aug23" 9054 if the entire string were given at once. Depending on the application, 9055 this may or may not be what you want. The only way to allow for start- 9056 ing again at the next character is to retain the matched part of the 9057 subject and try a new complete match. 9058 9059 You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with 9060 PCRE_DFA_RESTART to continue partial matching over multiple segments. 9061 This facility can be used to pass very long subject strings to the DFA 9062 matching functions. 9063 9064 9065MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre[16|32]_exec() 9066 9067 From release 8.00, the standard matching functions can also be used to 9068 do multi-segment matching. Unlike the DFA functions, it is not possible 9069 to restart the previous match with a new segment of data. Instead, new 9070 data must be added to the previous subject string, and the entire match 9071 re-run, starting from the point where the partial match occurred. Ear- 9072 lier data can be discarded. 9073 9074 It is best to use PCRE_PARTIAL_HARD in this situation, because it does 9075 not treat the end of a segment as the end of the subject when matching 9076 \z, \Z, \b, \B, and $. Consider an unanchored pattern that matches 9077 dates: 9078 9079 re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/ 9080 data> The date is 23ja\P\P 9081 Partial match: 23ja 9082 9083 At this stage, an application could discard the text preceding "23ja", 9084 add on text from the next segment, and call the matching function 9085 again. Unlike the DFA matching functions, the entire matching string 9086 must always be available, and the complete matching process occurs for 9087 each call, so more memory and more processing time is needed. 9088 9089 Note: If the pattern contains lookbehind assertions, or \K, or starts 9090 with \b or \B, the string that is returned for a partial match includes 9091 characters that precede the start of what would be returned for a com- 9092 plete match, because it contains all the characters that were inspected 9093 during the partial match. 9094 9095 9096ISSUES WITH MULTI-SEGMENT MATCHING 9097 9098 Certain types of pattern may give problems with multi-segment matching, 9099 whichever matching function is used. 9100 9101 1. If the pattern contains a test for the beginning of a line, you need 9102 to pass the PCRE_NOTBOL option when the subject string for any call 9103 does start at the beginning of a line. There is also a PCRE_NOTEOL 9104 option, but in practice when doing multi-segment matching you should be 9105 using PCRE_PARTIAL_HARD, which includes the effect of PCRE_NOTEOL. 9106 9107 2. Lookbehind assertions that have already been obeyed are catered for 9108 in the offsets that are returned for a partial match. However a lookbe- 9109 hind assertion later in the pattern could require even earlier charac- 9110 ters to be inspected. You can handle this case by using the 9111 PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or 9112 pcre[16|32]_fullinfo() functions to obtain the length of the longest 9113 lookbehind in the pattern. This length is given in characters, not 9114 bytes. If you always retain at least that many characters before the 9115 partially matched string, all should be well. (Of course, near the 9116 start of the subject, fewer characters may be present; in that case all 9117 characters should be retained.) 9118 9119 From release 8.33, there is a more accurate way of deciding which char- 9120 acters to retain. Instead of subtracting the length of the longest 9121 lookbehind from the earliest inspected character (offsets[0]), the 9122 match start position (offsets[2]) should be used, and the next match 9123 attempt started at the offsets[2] character by setting the startoffset 9124 argument of pcre_exec() or pcre_dfa_exec(). 9125 9126 For example, if the pattern "(?<=123)abc" is partially matched against 9127 the string "xx123a", the three offset values returned are 2, 6, and 5. 9128 This indicates that the matching process that gave a partial match 9129 started at offset 5, but the characters "123a" were all inspected. The 9130 maximum lookbehind for that pattern is 3, so taking that away from 5 9131 shows that we need only keep "123a", and the next match attempt can be 9132 started at offset 3 (that is, at "a") when further characters have been 9133 added. When the match start is not the earliest inspected character, 9134 pcretest shows it explicitly: 9135 9136 re> "(?<=123)abc" 9137 data> xx123a\P\P 9138 Partial match at offset 5: 123a 9139 9140 3. Because a partial match must always contain at least one character, 9141 what might be considered a partial match of an empty string actually 9142 gives a "no match" result. For example: 9143 9144 re> /c(?<=abc)x/ 9145 data> ab\P 9146 No match 9147 9148 If the next segment begins "cx", a match should be found, but this will 9149 only happen if characters from the previous segment are retained. For 9150 this reason, a "no match" result should be interpreted as "partial 9151 match of an empty string" when the pattern contains lookbehinds. 9152 9153 4. Matching a subject string that is split into multiple segments may 9154 not always produce exactly the same result as matching over one single 9155 long string, especially when PCRE_PARTIAL_SOFT is used. The section 9156 "Partial Matching and Word Boundaries" above describes an issue that 9157 arises if the pattern ends with \b or \B. Another kind of difference 9158 may occur when there are multiple matching possibilities, because (for 9159 PCRE_PARTIAL_SOFT) a partial match result is given only when there are 9160 no completed matches. This means that as soon as the shortest match has 9161 been found, continuation to a new subject segment is no longer possi- 9162 ble. Consider again this pcretest example: 9163 9164 re> /dog(sbody)?/ 9165 data> dogsb\P 9166 0: dog 9167 data> do\P\D 9168 Partial match: do 9169 data> gsb\R\P\D 9170 0: g 9171 data> dogsbody\D 9172 0: dogsbody 9173 1: dog 9174 9175 The first data line passes the string "dogsb" to a standard matching 9176 function, setting the PCRE_PARTIAL_SOFT option. Although the string is 9177 a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL, 9178 because the shorter string "dog" is a complete match. Similarly, when 9179 the subject is presented to a DFA matching function in several parts 9180 ("do" and "gsb" being the first two) the match stops when "dog" has 9181 been found, and it is not possible to continue. On the other hand, if 9182 "dogsbody" is presented as a single string, a DFA matching function 9183 finds both matches. 9184 9185 Because of these problems, it is best to use PCRE_PARTIAL_HARD when 9186 matching multi-segment data. The example above then behaves differ- 9187 ently: 9188 9189 re> /dog(sbody)?/ 9190 data> dogsb\P\P 9191 Partial match: dogsb 9192 data> do\P\D 9193 Partial match: do 9194 data> gsb\R\P\P\D 9195 Partial match: gsb 9196 9197 5. Patterns that contain alternatives at the top level which do not all 9198 start with the same pattern item may not work as expected when 9199 PCRE_DFA_RESTART is used. For example, consider this pattern: 9200 9201 1234|3789 9202 9203 If the first part of the subject is "ABC123", a partial match of the 9204 first alternative is found at offset 3. There is no partial match for 9205 the second alternative, because such a match does not start at the same 9206 point in the subject string. Attempting to continue with the string 9207 "7890" does not yield a match because only those alternatives that 9208 match at one point in the subject are remembered. The problem arises 9209 because the start of the second alternative matches within the first 9210 alternative. There is no problem with anchored patterns or patterns 9211 such as: 9212 9213 1234|ABCD 9214 9215 where no string can be a partial match for both alternatives. This is 9216 not a problem if a standard matching function is used, because the 9217 entire match has to be rerun each time: 9218 9219 re> /1234|3789/ 9220 data> ABC123\P\P 9221 Partial match: 123 9222 data> 1237890 9223 0: 3789 9224 9225 Of course, instead of using PCRE_DFA_RESTART, the same technique of re- 9226 running the entire match can also be used with the DFA matching func- 9227 tions. Another possibility is to work with two buffers. If a partial 9228 match at offset n in the first buffer is followed by "no match" when 9229 PCRE_DFA_RESTART is used on the second buffer, you can then try a new 9230 match starting at offset n+1 in the first buffer. 9231 9232 9233AUTHOR 9234 9235 Philip Hazel 9236 University Computing Service 9237 Cambridge CB2 3QH, England. 9238 9239 9240REVISION 9241 9242 Last updated: 02 July 2013 9243 Copyright (c) 1997-2013 University of Cambridge. 9244------------------------------------------------------------------------------ 9245 9246 9247PCREPRECOMPILE(3) Library Functions Manual PCREPRECOMPILE(3) 9248 9249 9250 9251NAME 9252 PCRE - Perl-compatible regular expressions 9253 9254SAVING AND RE-USING PRECOMPILED PCRE PATTERNS 9255 9256 If you are running an application that uses a large number of regular 9257 expression patterns, it may be useful to store them in a precompiled 9258 form instead of having to compile them every time the application is 9259 run. If you are not using any private character tables (see the 9260 pcre_maketables() documentation), this is relatively straightforward. 9261 If you are using private tables, it is a little bit more complicated. 9262 However, if you are using the just-in-time optimization feature, it is 9263 not possible to save and reload the JIT data. 9264 9265 If you save compiled patterns to a file, you can copy them to a differ- 9266 ent host and run them there. If the two hosts have different endianness 9267 (byte order), you should run the pcre[16|32]_pat- 9268 tern_to_host_byte_order() function on the new host before trying to 9269 match the pattern. The matching functions return PCRE_ERROR_BADENDIAN- 9270 NESS if they detect a pattern with the wrong endianness. 9271 9272 Compiling regular expressions with one version of PCRE for use with a 9273 different version is not guaranteed to work and may cause crashes, and 9274 saving and restoring a compiled pattern loses any JIT optimization 9275 data. 9276 9277 9278SAVING A COMPILED PATTERN 9279 9280 The value returned by pcre[16|32]_compile() points to a single block of 9281 memory that holds the compiled pattern and associated data. You can 9282 find the length of this block in bytes by calling 9283 pcre[16|32]_fullinfo() with an argument of PCRE_INFO_SIZE. You can then 9284 save the data in any appropriate manner. Here is sample code for the 9285 8-bit library that compiles a pattern and writes it to a file. It 9286 assumes that the variable fd refers to a file that is open for output: 9287 9288 int erroroffset, rc, size; 9289 char *error; 9290 pcre *re; 9291 9292 re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL); 9293 if (re == NULL) { ... handle errors ... } 9294 rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size); 9295 if (rc < 0) { ... handle errors ... } 9296 rc = fwrite(re, 1, size, fd); 9297 if (rc != size) { ... handle errors ... } 9298 9299 In this example, the bytes that comprise the compiled pattern are 9300 copied exactly. Note that this is binary data that may contain any of 9301 the 256 possible byte values. On systems that make a distinction 9302 between binary and non-binary data, be sure that the file is opened for 9303 binary output. 9304 9305 If you want to write more than one pattern to a file, you will have to 9306 devise a way of separating them. For binary data, preceding each pat- 9307 tern with its length is probably the most straightforward approach. 9308 Another possibility is to write out the data in hexadecimal instead of 9309 binary, one pattern to a line. 9310 9311 Saving compiled patterns in a file is only one possible way of storing 9312 them for later use. They could equally well be saved in a database, or 9313 in the memory of some daemon process that passes them via sockets to 9314 the processes that want them. 9315 9316 If the pattern has been studied, it is also possible to save the normal 9317 study data in a similar way to the compiled pattern itself. However, if 9318 the PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is cre- 9319 ated cannot be saved because it is too dependent on the current envi- 9320 ronment. When studying generates additional information, 9321 pcre[16|32]_study() returns a pointer to a pcre[16|32]_extra data 9322 block. Its format is defined in the section on matching a pattern in 9323 the pcreapi documentation. The study_data field points to the binary 9324 study data, and this is what you must save (not the pcre[16|32]_extra 9325 block itself). The length of the study data can be obtained by calling 9326 pcre[16|32]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remem- 9327 ber to check that pcre[16|32]_study() did return a non-NULL value 9328 before trying to save the study data. 9329 9330 9331RE-USING A PRECOMPILED PATTERN 9332 9333 Re-using a precompiled pattern is straightforward. Having reloaded it 9334 into main memory, called pcre[16|32]_pattern_to_host_byte_order() if 9335 necessary, you pass its pointer to pcre[16|32]_exec() or 9336 pcre[16|32]_dfa_exec() in the usual way. 9337 9338 However, if you passed a pointer to custom character tables when the 9339 pattern was compiled (the tableptr argument of pcre[16|32]_compile()), 9340 you must now pass a similar pointer to pcre[16|32]_exec() or 9341 pcre[16|32]_dfa_exec(), because the value saved with the compiled pat- 9342 tern will obviously be nonsense. A field in a pcre[16|32]_extra() block 9343 is used to pass this data, as described in the section on matching a 9344 pattern in the pcreapi documentation. 9345 9346 Warning: The tables that pcre_exec() and pcre_dfa_exec() use must be 9347 the same as those that were used when the pattern was compiled. If this 9348 is not the case, the behaviour is undefined. 9349 9350 If you did not provide custom character tables when the pattern was 9351 compiled, the pointer in the compiled pattern is NULL, which causes the 9352 matching functions to use PCRE's internal tables. Thus, you do not need 9353 to take any special action at run time in this case. 9354 9355 If you saved study data with the compiled pattern, you need to create 9356 your own pcre[16|32]_extra data block and set the study_data field to 9357 point to the reloaded study data. You must also set the 9358 PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study 9359 data is present. Then pass the pcre[16|32]_extra block to the matching 9360 function in the usual way. If the pattern was studied for just-in-time 9361 optimization, that data cannot be saved, and so is lost by a 9362 save/restore cycle. 9363 9364 9365COMPATIBILITY WITH DIFFERENT PCRE RELEASES 9366 9367 In general, it is safest to recompile all saved patterns when you 9368 update to a new PCRE release, though not all updates actually require 9369 this. 9370 9371 9372AUTHOR 9373 9374 Philip Hazel 9375 University Computing Service 9376 Cambridge CB2 3QH, England. 9377 9378 9379REVISION 9380 9381 Last updated: 12 November 2013 9382 Copyright (c) 1997-2013 University of Cambridge. 9383------------------------------------------------------------------------------ 9384 9385 9386PCREPERFORM(3) Library Functions Manual PCREPERFORM(3) 9387 9388 9389 9390NAME 9391 PCRE - Perl-compatible regular expressions 9392 9393PCRE PERFORMANCE 9394 9395 Two aspects of performance are discussed below: memory usage and pro- 9396 cessing time. The way you express your pattern as a regular expression 9397 can affect both of them. 9398 9399 9400COMPILED PATTERN MEMORY USAGE 9401 9402 Patterns are compiled by PCRE into a reasonably efficient interpretive 9403 code, so that most simple patterns do not use much memory. However, 9404 there is one case where the memory usage of a compiled pattern can be 9405 unexpectedly large. If a parenthesized subpattern has a quantifier with 9406 a minimum greater than 1 and/or a limited maximum, the whole subpattern 9407 is repeated in the compiled code. For example, the pattern 9408 9409 (abc|def){2,4} 9410 9411 is compiled as if it were 9412 9413 (abc|def)(abc|def)((abc|def)(abc|def)?)? 9414 9415 (Technical aside: It is done this way so that backtrack points within 9416 each of the repetitions can be independently maintained.) 9417 9418 For regular expressions whose quantifiers use only small numbers, this 9419 is not usually a problem. However, if the numbers are large, and par- 9420 ticularly if such repetitions are nested, the memory usage can become 9421 an embarrassment. For example, the very simple pattern 9422 9423 ((ab){1,1000}c){1,3} 9424 9425 uses 51K bytes when compiled using the 8-bit library. When PCRE is com- 9426 piled with its default internal pointer size of two bytes, the size 9427 limit on a compiled pattern is 64K data units, and this is reached with 9428 the above pattern if the outer repetition is increased from 3 to 4. 9429 PCRE can be compiled to use larger internal pointers and thus handle 9430 larger compiled patterns, but it is better to try to rewrite your pat- 9431 tern to use less memory if you can. 9432 9433 One way of reducing the memory usage for such patterns is to make use 9434 of PCRE's "subroutine" facility. Re-writing the above pattern as 9435 9436 ((ab)(?2){0,999}c)(?1){0,2} 9437 9438 reduces the memory requirements to 18K, and indeed it remains under 20K 9439 even with the outer repetition increased to 100. However, this pattern 9440 is not exactly equivalent, because the "subroutine" calls are treated 9441 as atomic groups into which there can be no backtracking if there is a 9442 subsequent matching failure. Therefore, PCRE cannot do this kind of 9443 rewriting automatically. Furthermore, there is a noticeable loss of 9444 speed when executing the modified pattern. Nevertheless, if the atomic 9445 grouping is not a problem and the loss of speed is acceptable, this 9446 kind of rewriting will allow you to process patterns that PCRE cannot 9447 otherwise handle. 9448 9449 9450STACK USAGE AT RUN TIME 9451 9452 When pcre_exec() or pcre[16|32]_exec() is used for matching, certain 9453 kinds of pattern can cause it to use large amounts of the process 9454 stack. In some environments the default process stack is quite small, 9455 and if it runs out the result is often SIGSEGV. This issue is probably 9456 the most frequently raised problem with PCRE. Rewriting your pattern 9457 can often help. The pcrestack documentation discusses this issue in 9458 detail. 9459 9460 9461PROCESSING TIME 9462 9463 Certain items in regular expression patterns are processed more effi- 9464 ciently than others. It is more efficient to use a character class like 9465 [aeiou] than a set of single-character alternatives such as 9466 (a|e|i|o|u). In general, the simplest construction that provides the 9467 required behaviour is usually the most efficient. Jeffrey Friedl's book 9468 contains a lot of useful general discussion about optimizing regular 9469 expressions for efficient performance. This document contains a few 9470 observations about PCRE. 9471 9472 Using Unicode character properties (the \p, \P, and \X escapes) is 9473 slow, because PCRE has to use a multi-stage table lookup whenever it 9474 needs a character's property. If you can find an alternative pattern 9475 that does not use character properties, it will probably be faster. 9476 9477 By default, the escape sequences \b, \d, \s, and \w, and the POSIX 9478 character classes such as [:alpha:] do not use Unicode properties, 9479 partly for backwards compatibility, and partly for performance reasons. 9480 However, you can set PCRE_UCP if you want Unicode character properties 9481 to be used. This can double the matching time for items such as \d, 9482 when matched with a traditional matching function; the performance loss 9483 is less with a DFA matching function, and in both cases there is not 9484 much difference for \b. 9485 9486 When a pattern begins with .* not in parentheses, or in parentheses 9487 that are not the subject of a backreference, and the PCRE_DOTALL option 9488 is set, the pattern is implicitly anchored by PCRE, since it can match 9489 only at the start of a subject string. However, if PCRE_DOTALL is not 9490 set, PCRE cannot make this optimization, because the . metacharacter 9491 does not then match a newline, and if the subject string contains new- 9492 lines, the pattern may match from the character immediately following 9493 one of them instead of from the very start. For example, the pattern 9494 9495 .*second 9496 9497 matches the subject "first\nand second" (where \n stands for a newline 9498 character), with the match starting at the seventh character. In order 9499 to do this, PCRE has to retry the match starting after every newline in 9500 the subject. 9501 9502 If you are using such a pattern with subject strings that do not con- 9503 tain newlines, the best performance is obtained by setting PCRE_DOTALL, 9504 or starting the pattern with ^.* or ^.*? to indicate explicit anchor- 9505 ing. That saves PCRE from having to scan along the subject looking for 9506 a newline to restart at. 9507 9508 Beware of patterns that contain nested indefinite repeats. These can 9509 take a long time to run when applied to a string that does not match. 9510 Consider the pattern fragment 9511 9512 ^(a+)* 9513 9514 This can match "aaaa" in 16 different ways, and this number increases 9515 very rapidly as the string gets longer. (The * repeat can match 0, 1, 9516 2, 3, or 4 times, and for each of those cases other than 0 or 4, the + 9517 repeats can match different numbers of times.) When the remainder of 9518 the pattern is such that the entire match is going to fail, PCRE has in 9519 principle to try every possible variation, and this can take an 9520 extremely long time, even for relatively short strings. 9521 9522 An optimization catches some of the more simple cases such as 9523 9524 (a+)*b 9525 9526 where a literal character follows. Before embarking on the standard 9527 matching procedure, PCRE checks that there is a "b" later in the sub- 9528 ject string, and if there is not, it fails the match immediately. How- 9529 ever, when there is no following literal this optimization cannot be 9530 used. You can see the difference by comparing the behaviour of 9531 9532 (a+)*\d 9533 9534 with the pattern above. The former gives a failure almost instantly 9535 when applied to a whole line of "a" characters, whereas the latter 9536 takes an appreciable time with strings longer than about 20 characters. 9537 9538 In many cases, the solution to this kind of performance issue is to use 9539 an atomic group or a possessive quantifier. 9540 9541 9542AUTHOR 9543 9544 Philip Hazel 9545 University Computing Service 9546 Cambridge CB2 3QH, England. 9547 9548 9549REVISION 9550 9551 Last updated: 25 August 2012 9552 Copyright (c) 1997-2012 University of Cambridge. 9553------------------------------------------------------------------------------ 9554 9555 9556PCREPOSIX(3) Library Functions Manual PCREPOSIX(3) 9557 9558 9559 9560NAME 9561 PCRE - Perl-compatible regular expressions. 9562 9563SYNOPSIS 9564 9565 #include <pcreposix.h> 9566 9567 int regcomp(regex_t *preg, const char *pattern, 9568 int cflags); 9569 9570 int regexec(regex_t *preg, const char *string, 9571 size_t nmatch, regmatch_t pmatch[], int eflags); 9572 size_t regerror(int errcode, const regex_t *preg, 9573 char *errbuf, size_t errbuf_size); 9574 9575 void regfree(regex_t *preg); 9576 9577 9578DESCRIPTION 9579 9580 This set of functions provides a POSIX-style API for the PCRE regular 9581 expression 8-bit library. See the pcreapi documentation for a descrip- 9582 tion of PCRE's native API, which contains much additional functional- 9583 ity. There is no POSIX-style wrapper for PCRE's 16-bit and 32-bit 9584 library. 9585 9586 The functions described here are just wrapper functions that ultimately 9587 call the PCRE native API. Their prototypes are defined in the 9588 pcreposix.h header file, and on Unix systems the library itself is 9589 called pcreposix.a, so can be accessed by adding -lpcreposix to the 9590 command for linking an application that uses them. Because the POSIX 9591 functions call the native ones, it is also necessary to add -lpcre. 9592 9593 I have implemented only those POSIX option bits that can be reasonably 9594 mapped to PCRE native options. In addition, the option REG_EXTENDED is 9595 defined with the value zero. This has no effect, but since programs 9596 that are written to the POSIX interface often use it, this makes it 9597 easier to slot in PCRE as a replacement library. Other POSIX options 9598 are not even defined. 9599 9600 There are also some other options that are not defined by POSIX. These 9601 have been added at the request of users who want to make use of certain 9602 PCRE-specific features via the POSIX calling interface. 9603 9604 When PCRE is called via these functions, it is only the API that is 9605 POSIX-like in style. The syntax and semantics of the regular expres- 9606 sions themselves are still those of Perl, subject to the setting of 9607 various PCRE options, as described below. "POSIX-like in style" means 9608 that the API approximates to the POSIX definition; it is not fully 9609 POSIX-compatible, and in multi-byte encoding domains it is probably 9610 even less compatible. 9611 9612 The header for these functions is supplied as pcreposix.h to avoid any 9613 potential clash with other POSIX libraries. It can, of course, be 9614 renamed or aliased as regex.h, which is the "correct" name. It provides 9615 two structure types, regex_t for compiled internal forms, and reg- 9616 match_t for returning captured substrings. It also defines some con- 9617 stants whose names start with "REG_"; these are used for setting 9618 options and identifying error codes. 9619 9620 9621COMPILING A PATTERN 9622 9623 The function regcomp() is called to compile a pattern into an internal 9624 form. The pattern is a C string terminated by a binary zero, and is 9625 passed in the argument pattern. The preg argument is a pointer to a 9626 regex_t structure that is used as a base for storing information about 9627 the compiled regular expression. 9628 9629 The argument cflags is either zero, or contains one or more of the bits 9630 defined by the following macros: 9631 9632 REG_DOTALL 9633 9634 The PCRE_DOTALL option is set when the regular expression is passed for 9635 compilation to the native function. Note that REG_DOTALL is not part of 9636 the POSIX standard. 9637 9638 REG_ICASE 9639 9640 The PCRE_CASELESS option is set when the regular expression is passed 9641 for compilation to the native function. 9642 9643 REG_NEWLINE 9644 9645 The PCRE_MULTILINE option is set when the regular expression is passed 9646 for compilation to the native function. Note that this does not mimic 9647 the defined POSIX behaviour for REG_NEWLINE (see the following sec- 9648 tion). 9649 9650 REG_NOSUB 9651 9652 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is 9653 passed for compilation to the native function. In addition, when a pat- 9654 tern that is compiled with this flag is passed to regexec() for match- 9655 ing, the nmatch and pmatch arguments are ignored, and no captured 9656 strings are returned. 9657 9658 REG_UCP 9659 9660 The PCRE_UCP option is set when the regular expression is passed for 9661 compilation to the native function. This causes PCRE to use Unicode 9662 properties when matchine \d, \w, etc., instead of just recognizing 9663 ASCII values. Note that REG_UTF8 is not part of the POSIX standard. 9664 9665 REG_UNGREEDY 9666 9667 The PCRE_UNGREEDY option is set when the regular expression is passed 9668 for compilation to the native function. Note that REG_UNGREEDY is not 9669 part of the POSIX standard. 9670 9671 REG_UTF8 9672 9673 The PCRE_UTF8 option is set when the regular expression is passed for 9674 compilation to the native function. This causes the pattern itself and 9675 all data strings used for matching it to be treated as UTF-8 strings. 9676 Note that REG_UTF8 is not part of the POSIX standard. 9677 9678 In the absence of these flags, no options are passed to the native 9679 function. This means the the regex is compiled with PCRE default 9680 semantics. In particular, the way it handles newline characters in the 9681 subject string is the Perl way, not the POSIX way. Note that setting 9682 PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE. 9683 It does not affect the way newlines are matched by . (they are not) or 9684 by a negative class such as [^a] (they are). 9685 9686 The yield of regcomp() is zero on success, and non-zero otherwise. The 9687 preg structure is filled in on success, and one member of the structure 9688 is public: re_nsub contains the number of capturing subpatterns in the 9689 regular expression. Various error codes are defined in the header file. 9690 9691 NOTE: If the yield of regcomp() is non-zero, you must not attempt to 9692 use the contents of the preg structure. If, for example, you pass it to 9693 regexec(), the result is undefined and your program is likely to crash. 9694 9695 9696MATCHING NEWLINE CHARACTERS 9697 9698 This area is not simple, because POSIX and Perl take different views of 9699 things. It is not possible to get PCRE to obey POSIX semantics, but 9700 then PCRE was never intended to be a POSIX engine. The following table 9701 lists the different possibilities for matching newline characters in 9702 PCRE: 9703 9704 Default Change with 9705 9706 . matches newline no PCRE_DOTALL 9707 newline matches [^a] yes not changeable 9708 $ matches \n at end yes PCRE_DOLLARENDONLY 9709 $ matches \n in middle no PCRE_MULTILINE 9710 ^ matches \n in middle no PCRE_MULTILINE 9711 9712 This is the equivalent table for POSIX: 9713 9714 Default Change with 9715 9716 . matches newline yes REG_NEWLINE 9717 newline matches [^a] yes REG_NEWLINE 9718 $ matches \n at end no REG_NEWLINE 9719 $ matches \n in middle no REG_NEWLINE 9720 ^ matches \n in middle no REG_NEWLINE 9721 9722 PCRE's behaviour is the same as Perl's, except that there is no equiva- 9723 lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is 9724 no way to stop newline from matching [^a]. 9725 9726 The default POSIX newline handling can be obtained by setting 9727 PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE 9728 behave exactly as for the REG_NEWLINE action. 9729 9730 9731MATCHING A PATTERN 9732 9733 The function regexec() is called to match a compiled pattern preg 9734 against a given string, which is by default terminated by a zero byte 9735 (but see REG_STARTEND below), subject to the options in eflags. These 9736 can be: 9737 9738 REG_NOTBOL 9739 9740 The PCRE_NOTBOL option is set when calling the underlying PCRE matching 9741 function. 9742 9743 REG_NOTEMPTY 9744 9745 The PCRE_NOTEMPTY option is set when calling the underlying PCRE match- 9746 ing function. Note that REG_NOTEMPTY is not part of the POSIX standard. 9747 However, setting this option can give more POSIX-like behaviour in some 9748 situations. 9749 9750 REG_NOTEOL 9751 9752 The PCRE_NOTEOL option is set when calling the underlying PCRE matching 9753 function. 9754 9755 REG_STARTEND 9756 9757 The string is considered to start at string + pmatch[0].rm_so and to 9758 have a terminating NUL located at string + pmatch[0].rm_eo (there need 9759 not actually be a NUL at that location), regardless of the value of 9760 nmatch. This is a BSD extension, compatible with but not specified by 9761 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in 9762 software intended to be portable to other systems. Note that a non-zero 9763 rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location 9764 of the string, not how it is matched. 9765 9766 If the pattern was compiled with the REG_NOSUB flag, no data about any 9767 matched strings is returned. The nmatch and pmatch arguments of 9768 regexec() are ignored. 9769 9770 If the value of nmatch is zero, or if the value pmatch is NULL, no data 9771 about any matched strings is returned. 9772 9773 Otherwise,the portion of the string that was matched, and also any cap- 9774 tured substrings, are returned via the pmatch argument, which points to 9775 an array of nmatch structures of type regmatch_t, containing the mem- 9776 bers rm_so and rm_eo. These contain the offset to the first character 9777 of each substring and the offset to the first character after the end 9778 of each substring, respectively. The 0th element of the vector relates 9779 to the entire portion of string that was matched; subsequent elements 9780 relate to the capturing subpatterns of the regular expression. Unused 9781 entries in the array have both structure members set to -1. 9782 9783 A successful match yields a zero return; various error codes are 9784 defined in the header file, of which REG_NOMATCH is the "expected" 9785 failure code. 9786 9787 9788ERROR MESSAGES 9789 9790 The regerror() function maps a non-zero errorcode from either regcomp() 9791 or regexec() to a printable message. If preg is not NULL, the error 9792 should have arisen from the use of that structure. A message terminated 9793 by a binary zero is placed in errbuf. The length of the message, 9794 including the zero, is limited to errbuf_size. The yield of the func- 9795 tion is the size of buffer needed to hold the whole message. 9796 9797 9798MEMORY USAGE 9799 9800 Compiling a regular expression causes memory to be allocated and asso- 9801 ciated with the preg structure. The function regfree() frees all such 9802 memory, after which preg may no longer be used as a compiled expres- 9803 sion. 9804 9805 9806AUTHOR 9807 9808 Philip Hazel 9809 University Computing Service 9810 Cambridge CB2 3QH, England. 9811 9812 9813REVISION 9814 9815 Last updated: 09 January 2012 9816 Copyright (c) 1997-2012 University of Cambridge. 9817------------------------------------------------------------------------------ 9818 9819 9820PCRECPP(3) Library Functions Manual PCRECPP(3) 9821 9822 9823 9824NAME 9825 PCRE - Perl-compatible regular expressions. 9826 9827SYNOPSIS OF C++ WRAPPER 9828 9829 #include <pcrecpp.h> 9830 9831 9832DESCRIPTION 9833 9834 The C++ wrapper for PCRE was provided by Google Inc. Some additional 9835 functionality was added by Giuseppe Maxia. This brief man page was con- 9836 structed from the notes in the pcrecpp.h file, which should be con- 9837 sulted for further details. Note that the C++ wrapper supports only the 9838 original 8-bit PCRE library. There is no 16-bit or 32-bit support at 9839 present. 9840 9841 9842MATCHING INTERFACE 9843 9844 The "FullMatch" operation checks that supplied text matches a supplied 9845 pattern exactly. If pointer arguments are supplied, it copies matched 9846 sub-strings that match sub-patterns into them. 9847 9848 Example: successful match 9849 pcrecpp::RE re("h.*o"); 9850 re.FullMatch("hello"); 9851 9852 Example: unsuccessful match (requires full match): 9853 pcrecpp::RE re("e"); 9854 !re.FullMatch("hello"); 9855 9856 Example: creating a temporary RE object: 9857 pcrecpp::RE("h.*o").FullMatch("hello"); 9858 9859 You can pass in a "const char*" or a "string" for "text". The examples 9860 below tend to use a const char*. You can, as in the different examples 9861 above, store the RE object explicitly in a variable or use a temporary 9862 RE object. The examples below use one mode or the other arbitrarily. 9863 Either could correctly be used for any of these examples. 9864 9865 You must supply extra pointer arguments to extract matched subpieces. 9866 9867 Example: extracts "ruby" into "s" and 1234 into "i" 9868 int i; 9869 string s; 9870 pcrecpp::RE re("(\\w+):(\\d+)"); 9871 re.FullMatch("ruby:1234", &s, &i); 9872 9873 Example: does not try to extract any extra sub-patterns 9874 re.FullMatch("ruby:1234", &s); 9875 9876 Example: does not try to extract into NULL 9877 re.FullMatch("ruby:1234", NULL, &i); 9878 9879 Example: integer overflow causes failure 9880 !re.FullMatch("ruby:1234567891234", NULL, &i); 9881 9882 Example: fails because there aren't enough sub-patterns: 9883 !pcrecpp::RE("\\w+:\\d+").FullMatch("ruby:1234", &s); 9884 9885 Example: fails because string cannot be stored in integer 9886 !pcrecpp::RE("(.*)").FullMatch("ruby", &i); 9887 9888 The provided pointer arguments can be pointers to any scalar numeric 9889 type, or one of: 9890 9891 string (matched piece is copied to string) 9892 StringPiece (StringPiece is mutated to point to matched piece) 9893 T (where "bool T::ParseFrom(const char*, int)" exists) 9894 NULL (the corresponding matched sub-pattern is not copied) 9895 9896 The function returns true iff all of the following conditions are sat- 9897 isfied: 9898 9899 a. "text" matches "pattern" exactly; 9900 9901 b. The number of matched sub-patterns is >= number of supplied 9902 pointers; 9903 9904 c. The "i"th argument has a suitable type for holding the 9905 string captured as the "i"th sub-pattern. If you pass in 9906 void * NULL for the "i"th argument, or a non-void * NULL 9907 of the correct type, or pass fewer arguments than the 9908 number of sub-patterns, "i"th captured sub-pattern is 9909 ignored. 9910 9911 CAVEAT: An optional sub-pattern that does not exist in the matched 9912 string is assigned the empty string. Therefore, the following will 9913 return false (because the empty string is not a valid number): 9914 9915 int number; 9916 pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number); 9917 9918 The matching interface supports at most 16 arguments per call. If you 9919 need more, consider using the more general interface 9920 pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch. 9921 9922 NOTE: Do not use no_arg, which is used internally to mark the end of a 9923 list of optional arguments, as a placeholder for missing arguments, as 9924 this can lead to segfaults. 9925 9926 9927QUOTING METACHARACTERS 9928 9929 You can use the "QuoteMeta" operation to insert backslashes before all 9930 potentially meaningful characters in a string. The returned string, 9931 used as a regular expression, will exactly match the original string. 9932 9933 Example: 9934 string quoted = RE::QuoteMeta(unquoted); 9935 9936 Note that it's legal to escape a character even if it has no special 9937 meaning in a regular expression -- so this function does that. (This 9938 also makes it identical to the perl function of the same name; see 9939 "perldoc -f quotemeta".) For example, "1.5-2.0?" becomes 9940 "1\.5\-2\.0\?". 9941 9942 9943PARTIAL MATCHES 9944 9945 You can use the "PartialMatch" operation when you want the pattern to 9946 match any substring of the text. 9947 9948 Example: simple search for a string: 9949 pcrecpp::RE("ell").PartialMatch("hello"); 9950 9951 Example: find first number in a string: 9952 int number; 9953 pcrecpp::RE re("(\\d+)"); 9954 re.PartialMatch("x*100 + 20", &number); 9955 assert(number == 100); 9956 9957 9958UTF-8 AND THE MATCHING INTERFACE 9959 9960 By default, pattern and text are plain text, one byte per character. 9961 The UTF8 flag, passed to the constructor, causes both pattern and 9962 string to be treated as UTF-8 text, still a byte stream but potentially 9963 multiple bytes per character. In practice, the text is likelier to be 9964 UTF-8 than the pattern, but the match returned may depend on the UTF8 9965 flag, so always use it when matching UTF8 text. For example, "." will 9966 match one byte normally but with UTF8 set may match up to three bytes 9967 of a multi-byte character. 9968 9969 Example: 9970 pcrecpp::RE_Options options; 9971 options.set_utf8(); 9972 pcrecpp::RE re(utf8_pattern, options); 9973 re.FullMatch(utf8_string); 9974 9975 Example: using the convenience function UTF8(): 9976 pcrecpp::RE re(utf8_pattern, pcrecpp::UTF8()); 9977 re.FullMatch(utf8_string); 9978 9979 NOTE: The UTF8 flag is ignored if pcre was not configured with the 9980 --enable-utf8 flag. 9981 9982 9983PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE 9984 9985 PCRE defines some modifiers to change the behavior of the regular 9986 expression engine. The C++ wrapper defines an auxiliary class, 9987 RE_Options, as a vehicle to pass such modifiers to a RE class. Cur- 9988 rently, the following modifiers are supported: 9989 9990 modifier description Perl corresponding 9991 9992 PCRE_CASELESS case insensitive match /i 9993 PCRE_MULTILINE multiple lines match /m 9994 PCRE_DOTALL dot matches newlines /s 9995 PCRE_DOLLAR_ENDONLY $ matches only at end N/A 9996 PCRE_EXTRA strict escape parsing N/A 9997 PCRE_EXTENDED ignore white spaces /x 9998 PCRE_UTF8 handles UTF8 chars built-in 9999 PCRE_UNGREEDY reverses * and *? N/A 10000 PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*) 10001 10002 (*) Both Perl and PCRE allow non capturing parentheses by means of the 10003 "?:" modifier within the pattern itself. e.g. (?:ab|cd) does not cap- 10004 ture, while (ab|cd) does. 10005 10006 For a full account on how each modifier works, please check the PCRE 10007 API reference page. 10008 10009 For each modifier, there are two member functions whose name is made 10010 out of the modifier in lowercase, without the "PCRE_" prefix. For 10011 instance, PCRE_CASELESS is handled by 10012 10013 bool caseless() 10014 10015 which returns true if the modifier is set, and 10016 10017 RE_Options & set_caseless(bool) 10018 10019 which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can 10020 be accessed through the set_match_limit() and match_limit() member 10021 functions. Setting match_limit to a non-zero value will limit the exe- 10022 cution of pcre to keep it from doing bad things like blowing the stack 10023 or taking an eternity to return a result. A value of 5000 is good 10024 enough to stop stack blowup in a 2MB thread stack. Setting match_limit 10025 to zero disables match limiting. Alternatively, you can call 10026 match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to 10027 limit how much PCRE recurses. match_limit() limits the number of 10028 matches PCRE does; match_limit_recursion() limits the depth of internal 10029 recursion, and therefore the amount of stack that is used. 10030 10031 Normally, to pass one or more modifiers to a RE class, you declare a 10032 RE_Options object, set the appropriate options, and pass this object to 10033 a RE constructor. Example: 10034 10035 RE_Options opt; 10036 opt.set_caseless(true); 10037 if (RE("HELLO", opt).PartialMatch("hello world")) ... 10038 10039 RE_options has two constructors. The default constructor takes no argu- 10040 ments and creates a set of flags that are off by default. The optional 10041 parameter option_flags is to facilitate transfer of legacy code from C 10042 programs. This lets you do 10043 10044 RE(pattern, 10045 RE_Options(PCRE_CASELESS|PCRE_MULTILINE)).PartialMatch(str); 10046 10047 However, new code is better off doing 10048 10049 RE(pattern, 10050 RE_Options().set_caseless(true).set_multiline(true)) 10051 .PartialMatch(str); 10052 10053 If you are going to pass one of the most used modifiers, there are some 10054 convenience functions that return a RE_Options class with the appropri- 10055 ate modifier already set: CASELESS(), UTF8(), MULTILINE(), DOTALL(), 10056 and EXTENDED(). 10057 10058 If you need to set several options at once, and you don't want to go 10059 through the pains of declaring a RE_Options object and setting several 10060 options, there is a parallel method that give you such ability on the 10061 fly. You can concatenate several set_xxxxx() member functions, since 10062 each of them returns a reference to its class object. For example, to 10063 pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one 10064 statement, you may write: 10065 10066 RE(" ^ xyz \\s+ .* blah$", 10067 RE_Options() 10068 .set_caseless(true) 10069 .set_extended(true) 10070 .set_multiline(true)).PartialMatch(sometext); 10071 10072 10073SCANNING TEXT INCREMENTALLY 10074 10075 The "Consume" operation may be useful if you want to repeatedly match 10076 regular expressions at the front of a string and skip over them as they 10077 match. This requires use of the "StringPiece" type, which represents a 10078 sub-range of a real string. Like RE, StringPiece is defined in the 10079 pcrecpp namespace. 10080 10081 Example: read lines of the form "var = value" from a string. 10082 string contents = ...; // Fill string somehow 10083 pcrecpp::StringPiece input(contents); // Wrap in a StringPiece 10084 10085 string var; 10086 int value; 10087 pcrecpp::RE re("(\\w+) = (\\d+)\n"); 10088 while (re.Consume(&input, &var, &value)) { 10089 ...; 10090 } 10091 10092 Each successful call to "Consume" will set "var/value", and also 10093 advance "input" so it points past the matched text. 10094 10095 The "FindAndConsume" operation is similar to "Consume" but does not 10096 anchor your match at the beginning of the string. For example, you 10097 could extract all words from a string by repeatedly calling 10098 10099 pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word) 10100 10101 10102PARSING HEX/OCTAL/C-RADIX NUMBERS 10103 10104 By default, if you pass a pointer to a numeric value, the corresponding 10105 text is interpreted as a base-10 number. You can instead wrap the 10106 pointer with a call to one of the operators Hex(), Octal(), or CRadix() 10107 to interpret the text in another base. The CRadix operator interprets 10108 C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to 10109 base-10. 10110 10111 Example: 10112 int a, b, c, d; 10113 pcrecpp::RE re("(.*) (.*) (.*) (.*)"); 10114 re.FullMatch("100 40 0100 0x40", 10115 pcrecpp::Octal(&a), pcrecpp::Hex(&b), 10116 pcrecpp::CRadix(&c), pcrecpp::CRadix(&d)); 10117 10118 will leave 64 in a, b, c, and d. 10119 10120 10121REPLACING PARTS OF STRINGS 10122 10123 You can replace the first match of "pattern" in "str" with "rewrite". 10124 Within "rewrite", backslash-escaped digits (\1 to \9) can be used to 10125 insert text matching corresponding parenthesized group from the pat- 10126 tern. \0 in "rewrite" refers to the entire matching text. For example: 10127 10128 string s = "yabba dabba doo"; 10129 pcrecpp::RE("b+").Replace("d", &s); 10130 10131 will leave "s" containing "yada dabba doo". The result is true if the 10132 pattern matches and a replacement occurs, false otherwise. 10133 10134 GlobalReplace is like Replace except that it replaces all occurrences 10135 of the pattern in the string with the rewrite. Replacements are not 10136 subject to re-matching. For example: 10137 10138 string s = "yabba dabba doo"; 10139 pcrecpp::RE("b+").GlobalReplace("d", &s); 10140 10141 will leave "s" containing "yada dada doo". It returns the number of 10142 replacements made. 10143 10144 Extract is like Replace, except that if the pattern matches, "rewrite" 10145 is copied into "out" (an additional argument) with substitutions. The 10146 non-matching portions of "text" are ignored. Returns true iff a match 10147 occurred and the extraction happened successfully; if no match occurs, 10148 the string is left unaffected. 10149 10150 10151AUTHOR 10152 10153 The C++ wrapper was contributed by Google Inc. 10154 Copyright (c) 2007 Google Inc. 10155 10156 10157REVISION 10158 10159 Last updated: 08 January 2012 10160------------------------------------------------------------------------------ 10161 10162 10163PCRESAMPLE(3) Library Functions Manual PCRESAMPLE(3) 10164 10165 10166 10167NAME 10168 PCRE - Perl-compatible regular expressions 10169 10170PCRE SAMPLE PROGRAM 10171 10172 A simple, complete demonstration program, to get you started with using 10173 PCRE, is supplied in the file pcredemo.c in the PCRE distribution. A 10174 listing of this program is given in the pcredemo documentation. If you 10175 do not have a copy of the PCRE distribution, you can save this listing 10176 to re-create pcredemo.c. 10177 10178 The demonstration program, which uses the original PCRE 8-bit library, 10179 compiles the regular expression that is its first argument, and matches 10180 it against the subject string in its second argument. No PCRE options 10181 are set, and default character tables are used. If matching succeeds, 10182 the program outputs the portion of the subject that matched, together 10183 with the contents of any captured substrings. 10184 10185 If the -g option is given on the command line, the program then goes on 10186 to check for further matches of the same regular expression in the same 10187 subject string. The logic is a little bit tricky because of the possi- 10188 bility of matching an empty string. Comments in the code explain what 10189 is going on. 10190 10191 If PCRE is installed in the standard include and library directories 10192 for your operating system, you should be able to compile the demonstra- 10193 tion program using this command: 10194 10195 gcc -o pcredemo pcredemo.c -lpcre 10196 10197 If PCRE is installed elsewhere, you may need to add additional options 10198 to the command line. For example, on a Unix-like system that has PCRE 10199 installed in /usr/local, you can compile the demonstration program 10200 using a command like this: 10201 10202 gcc -o pcredemo -I/usr/local/include pcredemo.c \ 10203 -L/usr/local/lib -lpcre 10204 10205 In a Windows environment, if you want to statically link the program 10206 against a non-dll pcre.a file, you must uncomment the line that defines 10207 PCRE_STATIC before including pcre.h, because otherwise the pcre_mal- 10208 loc() and pcre_free() exported functions will be declared 10209 __declspec(dllimport), with unwanted results. 10210 10211 Once you have compiled and linked the demonstration program, you can 10212 run simple tests like this: 10213 10214 ./pcredemo 'cat|dog' 'the cat sat on the mat' 10215 ./pcredemo -g 'cat|dog' 'the dog sat on the cat' 10216 10217 Note that there is a much more comprehensive test program, called 10218 pcretest, which supports many more facilities for testing regular 10219 expressions and both PCRE libraries. The pcredemo program is provided 10220 as a simple coding example. 10221 10222 If you try to run pcredemo when PCRE is not installed in the standard 10223 library directory, you may get an error like this on some operating 10224 systems (e.g. Solaris): 10225 10226 ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or 10227 directory 10228 10229 This is caused by the way shared library support works on those sys- 10230 tems. You need to add 10231 10232 -R/usr/local/lib 10233 10234 (for example) to the compile command to get round this problem. 10235 10236 10237AUTHOR 10238 10239 Philip Hazel 10240 University Computing Service 10241 Cambridge CB2 3QH, England. 10242 10243 10244REVISION 10245 10246 Last updated: 10 January 2012 10247 Copyright (c) 1997-2012 University of Cambridge. 10248------------------------------------------------------------------------------ 10249PCRELIMITS(3) Library Functions Manual PCRELIMITS(3) 10250 10251 10252 10253NAME 10254 PCRE - Perl-compatible regular expressions 10255 10256SIZE AND OTHER LIMITATIONS 10257 10258 There are some size limitations in PCRE but it is hoped that they will 10259 never in practice be relevant. 10260 10261 The maximum length of a compiled pattern is approximately 64K data 10262 units (bytes for the 8-bit library, 16-bit units for the 16-bit 10263 library, and 32-bit units for the 32-bit library) if PCRE is compiled 10264 with the default internal linkage size, which is 2 bytes for the 8-bit 10265 and 16-bit libraries, and 4 bytes for the 32-bit library. If you want 10266 to process regular expressions that are truly enormous, you can compile 10267 PCRE with an internal linkage size of 3 or 4 (when building the 16-bit 10268 or 32-bit library, 3 is rounded up to 4). See the README file in the 10269 source distribution and the pcrebuild documentation for details. In 10270 these cases the limit is substantially larger. However, the speed of 10271 execution is slower. 10272 10273 All values in repeating quantifiers must be less than 65536. 10274 10275 There is no limit to the number of parenthesized subpatterns, but there 10276 can be no more than 65535 capturing subpatterns. There is, however, a 10277 limit to the depth of nesting of parenthesized subpatterns of all 10278 kinds. This is imposed in order to limit the amount of system stack 10279 used at compile time. The limit can be specified when PCRE is built; 10280 the default is 250. 10281 10282 There is a limit to the number of forward references to subsequent sub- 10283 patterns of around 200,000. Repeated forward references with fixed 10284 upper limits, for example, (?2){0,100} when subpattern number 2 is to 10285 the right, are included in the count. There is no limit to the number 10286 of backward references. 10287 10288 The maximum length of name for a named subpattern is 32 characters, and 10289 the maximum number of named subpatterns is 10000. 10290 10291 The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or 10292 (*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit and 10293 32-bit libraries. 10294 10295 The maximum length of a subject string is the largest positive number 10296 that an integer variable can hold. However, when using the traditional 10297 matching function, PCRE uses recursion to handle subpatterns and indef- 10298 inite repetition. This means that the available stack space may limit 10299 the size of a subject string that can be processed by certain patterns. 10300 For a discussion of stack issues, see the pcrestack documentation. 10301 10302 10303AUTHOR 10304 10305 Philip Hazel 10306 University Computing Service 10307 Cambridge CB2 3QH, England. 10308 10309 10310REVISION 10311 10312 Last updated: 05 November 2013 10313 Copyright (c) 1997-2013 University of Cambridge. 10314------------------------------------------------------------------------------ 10315 10316 10317PCRESTACK(3) Library Functions Manual PCRESTACK(3) 10318 10319 10320 10321NAME 10322 PCRE - Perl-compatible regular expressions 10323 10324PCRE DISCUSSION OF STACK USAGE 10325 10326 When you call pcre[16|32]_exec(), it makes use of an internal function 10327 called match(). This calls itself recursively at branch points in the 10328 pattern, in order to remember the state of the match so that it can 10329 back up and try a different alternative if the first one fails. As 10330 matching proceeds deeper and deeper into the tree of possibilities, the 10331 recursion depth increases. The match() function is also called in other 10332 circumstances, for example, whenever a parenthesized sub-pattern is 10333 entered, and in certain cases of repetition. 10334 10335 Not all calls of match() increase the recursion depth; for an item such 10336 as a* it may be called several times at the same level, after matching 10337 different numbers of a's. Furthermore, in a number of cases where the 10338 result of the recursive call would immediately be passed back as the 10339 result of the current call (a "tail recursion"), the function is just 10340 restarted instead. 10341 10342 The above comments apply when pcre[16|32]_exec() is run in its normal 10343 interpretive manner. If the pattern was studied with the 10344 PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was success- 10345 ful, and the options passed to pcre[16|32]_exec() were not incompati- 10346 ble, the matching process uses the JIT-compiled code instead of the 10347 match() function. In this case, the memory requirements are handled 10348 entirely differently. See the pcrejit documentation for details. 10349 10350 The pcre[16|32]_dfa_exec() function operates in an entirely different 10351 way, and uses recursion only when there is a regular expression recur- 10352 sion or subroutine call in the pattern. This includes the processing of 10353 assertion and "once-only" subpatterns, which are handled like subrou- 10354 tine calls. Normally, these are never very deep, and the limit on the 10355 complexity of pcre[16|32]_dfa_exec() is controlled by the amount of 10356 workspace it is given. However, it is possible to write patterns with 10357 runaway infinite recursions; such patterns will cause 10358 pcre[16|32]_dfa_exec() to run out of stack. At present, there is no 10359 protection against this. 10360 10361 The comments that follow do NOT apply to pcre[16|32]_dfa_exec(); they 10362 are relevant only for pcre[16|32]_exec() without the JIT optimization. 10363 10364 Reducing pcre[16|32]_exec()'s stack usage 10365 10366 Each time that match() is actually called recursively, it uses memory 10367 from the process stack. For certain kinds of pattern and data, very 10368 large amounts of stack may be needed, despite the recognition of "tail 10369 recursion". You can often reduce the amount of recursion, and there- 10370 fore the amount of stack used, by modifying the pattern that is being 10371 matched. Consider, for example, this pattern: 10372 10373 ([^<]|<(?!inet))+ 10374 10375 It matches from wherever it starts until it encounters "<inet" or the 10376 end of the data, and is the kind of pattern that might be used when 10377 processing an XML file. Each iteration of the outer parentheses matches 10378 either one character that is not "<" or a "<" that is not followed by 10379 "inet". However, each time a parenthesis is processed, a recursion 10380 occurs, so this formulation uses a stack frame for each matched charac- 10381 ter. For a long string, a lot of stack is required. Consider now this 10382 rewritten pattern, which matches exactly the same strings: 10383 10384 ([^<]++|<(?!inet))+ 10385 10386 This uses very much less stack, because runs of characters that do not 10387 contain "<" are "swallowed" in one item inside the parentheses. Recur- 10388 sion happens only when a "<" character that is not followed by "inet" 10389 is encountered (and we assume this is relatively rare). A possessive 10390 quantifier is used to stop any backtracking into the runs of non-"<" 10391 characters, but that is not related to stack usage. 10392 10393 This example shows that one way of avoiding stack problems when match- 10394 ing long subject strings is to write repeated parenthesized subpatterns 10395 to match more than one character whenever possible. 10396 10397 Compiling PCRE to use heap instead of stack for pcre[16|32]_exec() 10398 10399 In environments where stack memory is constrained, you might want to 10400 compile PCRE to use heap memory instead of stack for remembering back- 10401 up points when pcre[16|32]_exec() is running. This makes it run a lot 10402 more slowly, however. Details of how to do this are given in the pcre- 10403 build documentation. When built in this way, instead of using the 10404 stack, PCRE obtains and frees memory by calling the functions that are 10405 pointed to by the pcre[16|32]_stack_malloc and pcre[16|32]_stack_free 10406 variables. By default, these point to malloc() and free(), but you can 10407 replace the pointers to cause PCRE to use your own functions. Since the 10408 block sizes are always the same, and are always freed in reverse order, 10409 it may be possible to implement customized memory handlers that are 10410 more efficient than the standard functions. 10411 10412 Limiting pcre[16|32]_exec()'s stack usage 10413 10414 You can set limits on the number of times that match() is called, both 10415 in total and recursively. If a limit is exceeded, pcre[16|32]_exec() 10416 returns an error code. Setting suitable limits should prevent it from 10417 running out of stack. The default values of the limits are very large, 10418 and unlikely ever to operate. They can be changed when PCRE is built, 10419 and they can also be set when pcre[16|32]_exec() is called. For details 10420 of these interfaces, see the pcrebuild documentation and the section on 10421 extra data for pcre[16|32]_exec() in the pcreapi documentation. 10422 10423 As a very rough rule of thumb, you should reckon on about 500 bytes per 10424 recursion. Thus, if you want to limit your stack usage to 8Mb, you 10425 should set the limit at 16000 recursions. A 64Mb stack, on the other 10426 hand, can support around 128000 recursions. 10427 10428 In Unix-like environments, the pcretest test program has a command line 10429 option (-S) that can be used to increase the size of its stack. As long 10430 as the stack is large enough, another option (-M) can be used to find 10431 the smallest limits that allow a particular pattern to match a given 10432 subject string. This is done by calling pcre[16|32]_exec() repeatedly 10433 with different limits. 10434 10435 Obtaining an estimate of stack usage 10436 10437 The actual amount of stack used per recursion can vary quite a lot, 10438 depending on the compiler that was used to build PCRE and the optimiza- 10439 tion or debugging options that were set for it. The rule of thumb value 10440 of 500 bytes mentioned above may be larger or smaller than what is 10441 actually needed. A better approximation can be obtained by running this 10442 command: 10443 10444 pcretest -m -C 10445 10446 The -C option causes pcretest to output information about the options 10447 with which PCRE was compiled. When -m is also given (before -C), infor- 10448 mation about stack use is given in a line like this: 10449 10450 Match recursion uses stack: approximate frame size = 640 bytes 10451 10452 The value is approximate because some recursions need a bit more (up to 10453 perhaps 16 more bytes). 10454 10455 If the above command is given when PCRE is compiled to use the heap 10456 instead of the stack for recursion, the value that is output is the 10457 size of each block that is obtained from the heap. 10458 10459 Changing stack size in Unix-like systems 10460 10461 In Unix-like environments, there is not often a problem with the stack 10462 unless very long strings are involved, though the default limit on 10463 stack size varies from system to system. Values from 8Mb to 64Mb are 10464 common. You can find your default limit by running the command: 10465 10466 ulimit -s 10467 10468 Unfortunately, the effect of running out of stack is often SIGSEGV, 10469 though sometimes a more explicit error message is given. You can nor- 10470 mally increase the limit on stack size by code such as this: 10471 10472 struct rlimit rlim; 10473 getrlimit(RLIMIT_STACK, &rlim); 10474 rlim.rlim_cur = 100*1024*1024; 10475 setrlimit(RLIMIT_STACK, &rlim); 10476 10477 This reads the current limits (soft and hard) using getrlimit(), then 10478 attempts to increase the soft limit to 100Mb using setrlimit(). You 10479 must do this before calling pcre[16|32]_exec(). 10480 10481 Changing stack size in Mac OS X 10482 10483 Using setrlimit(), as described above, should also work on Mac OS X. It 10484 is also possible to set a stack size when linking a program. There is a 10485 discussion about stack sizes in Mac OS X at this web site: 10486 http://developer.apple.com/qa/qa2005/qa1419.html. 10487 10488 10489AUTHOR 10490 10491 Philip Hazel 10492 University Computing Service 10493 Cambridge CB2 3QH, England. 10494 10495 10496REVISION 10497 10498 Last updated: 24 June 2012 10499 Copyright (c) 1997-2012 University of Cambridge. 10500------------------------------------------------------------------------------ 10501 10502 10503
