1<!-- 2Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3 4SPDX-License-Identifier: curl 5--> 6 7# curl tutorial 8 9## Simple Usage 10 11Get the main page from a web-server: 12 13 curl https://www.example.com/ 14 15Get a README file from an FTP server: 16 17 curl ftp://ftp.example.com/README 18 19Get a webpage from a server using port 8000: 20 21 curl http://www.example.com:8000/ 22 23Get a directory listing of an FTP site: 24 25 curl ftp://ftp.example.com/ 26 27Get the all terms matching curl from a dictionary: 28 29 curl dict://dict.example.com/m:curl 30 31Get the definition of curl from a dictionary: 32 33 curl dict://dict.example.com/d:curl 34 35Fetch two documents at once: 36 37 curl ftp://ftp.example.com/ http://www.example.com:8000/ 38 39Get a file off an FTPS server: 40 41 curl ftps://files.are.example.com/secrets.txt 42 43or use the more appropriate FTPS way to get the same file: 44 45 curl --ftp-ssl ftp://files.are.example.com/secrets.txt 46 47Get a file from an SSH server using SFTP: 48 49 curl -u username sftp://example.com/etc/issue 50 51Get a file from an SSH server using SCP using a private key (not 52password-protected) to authenticate: 53 54 curl -u username: --key ~/.ssh/id_rsa scp://example.com/~/file.txt 55 56Get a file from an SSH server using SCP using a private key 57(password-protected) to authenticate: 58 59 curl -u username: --key ~/.ssh/id_rsa --pass private_key_password 60 scp://example.com/~/file.txt 61 62Get the main page from an IPv6 web server: 63 64 curl "http://[2001:1890:1112:1::20]/" 65 66Get a file from an SMB server: 67 68 curl -u "domain\username:passwd" smb://server.example.com/share/file.txt 69 70## Download to a File 71 72Get a webpage and store in a local file with a specific name: 73 74 curl -o thatpage.html http://www.example.com/ 75 76Get a webpage and store in a local file, make the local file get the name of 77the remote document (if no filename part is specified in the URL, this fails): 78 79 curl -O http://www.example.com/index.html 80 81Fetch two files and store them with their remote names: 82 83 curl -O www.haxx.se/index.html -O curl.se/download.html 84 85## Using Passwords 86 87### FTP 88 89To ftp files using name and password, include them in the URL like: 90 91 curl ftp://name:passwd@ftp.server.example:port/full/path/to/file 92 93or specify them with the `-u` flag like 94 95 curl -u name:passwd ftp://ftp.server.example:port/full/path/to/file 96 97### FTPS 98 99It is just like for FTP, but you may also want to specify and use SSL-specific 100options for certificates etc. 101 102Note that using `FTPS://` as prefix is the *implicit* way as described in the 103standards while the recommended *explicit* way is done by using `FTP://` and 104the `--ssl-reqd` option. 105 106### SFTP / SCP 107 108This is similar to FTP, but you can use the `--key` option to specify a 109private key to use instead of a password. Note that the private key may itself 110be protected by a password that is unrelated to the login password of the 111remote system; this password is specified using the `--pass` option. 112Typically, curl automatically extracts the public key from the private key 113file, but in cases where curl does not have the proper library support, a 114matching public key file must be specified using the `--pubkey` option. 115 116### HTTP 117 118Curl also supports user and password in HTTP URLs, thus you can pick a file 119like: 120 121 curl http://name:passwd@http.server.example/full/path/to/file 122 123or specify user and password separately like in 124 125 curl -u name:passwd http://http.server.example/full/path/to/file 126 127HTTP offers many different methods of authentication and curl supports 128several: Basic, Digest, NTLM and Negotiate (SPNEGO). Without telling which 129method to use, curl defaults to Basic. You can also ask curl to pick the most 130secure ones out of the ones that the server accepts for the given URL, by 131using `--anyauth`. 132 133**Note**! According to the URL specification, HTTP URLs can not contain a user 134and password, so that style does not work when using curl via a proxy, even 135though curl allows it at other times. When using a proxy, you _must_ use the 136`-u` style for user and password. 137 138### HTTPS 139 140Probably most commonly used with private certificates, as explained below. 141 142## Proxy 143 144curl supports both HTTP and SOCKS proxy servers, with optional authentication. 145It does not have special support for FTP proxy servers since there are no 146standards for those, but it can still be made to work with many of them. You 147can also use both HTTP and SOCKS proxies to transfer files to and from FTP 148servers. 149 150Get an ftp file using an HTTP proxy named my-proxy that uses port 888: 151 152 curl -x my-proxy:888 ftp://ftp.example.com/README 153 154Get a file from an HTTP server that requires user and password, using the 155same proxy as above: 156 157 curl -u user:passwd -x my-proxy:888 http://www.example.com/ 158 159Some proxies require special authentication. Specify by using -U as above: 160 161 curl -U user:passwd -x my-proxy:888 http://www.example.com/ 162 163A comma-separated list of hosts and domains which do not use the proxy can be 164specified as: 165 166 curl --noproxy example.com -x my-proxy:888 http://www.example.com/ 167 168If the proxy is specified with `--proxy1.0` instead of `--proxy` or `-x`, then 169curl uses HTTP/1.0 instead of HTTP/1.1 for any `CONNECT` attempts. 170 171curl also supports SOCKS4 and SOCKS5 proxies with `--socks4` and `--socks5`. 172 173See also the environment variables Curl supports that offer further proxy 174control. 175 176Most FTP proxy servers are set up to appear as a normal FTP server from the 177client's perspective, with special commands to select the remote FTP server. 178curl supports the `-u`, `-Q` and `--ftp-account` options that can be used to 179set up transfers through many FTP proxies. For example, a file can be uploaded 180to a remote FTP server using a Blue Coat FTP proxy with the options: 181 182 curl -u "username@ftp.server.example Proxy-Username:Remote-Pass" 183 --ftp-account Proxy-Password --upload-file local-file 184 ftp://my-ftp.proxy.example:21/remote/upload/path/ 185 186See the manual for your FTP proxy to determine the form it expects to set up 187transfers, and curl's `-v` option to see exactly what curl is sending. 188 189## Piping 190 191Get a key file and add it with `apt-key` (when on a system that uses `apt` for 192package management): 193 194 curl -L https://apt.example.org/llvm-snapshot.gpg.key | sudo apt-key add - 195 196The '|' pipes the output to STDIN. `-` tells `apt-key` that the key file 197should be read from STDIN. 198 199## Ranges 200 201HTTP 1.1 introduced byte-ranges. Using this, a client can request to get only 202one or more sub-parts of a specified document. Curl supports this with the 203`-r` flag. 204 205Get the first 100 bytes of a document: 206 207 curl -r 0-99 http://www.example.com/ 208 209Get the last 500 bytes of a document: 210 211 curl -r -500 http://www.example.com/ 212 213Curl also supports simple ranges for FTP files as well. Then you can only 214specify start and stop position. 215 216Get the first 100 bytes of a document using FTP: 217 218 curl -r 0-99 ftp://www.example.com/README 219 220## Uploading 221 222### FTP / FTPS / SFTP / SCP 223 224Upload all data on stdin to a specified server: 225 226 curl -T - ftp://ftp.example.com/myfile 227 228Upload data from a specified file, login with user and password: 229 230 curl -T uploadfile -u user:passwd ftp://ftp.example.com/myfile 231 232Upload a local file to the remote site, and use the local filename at the 233remote site too: 234 235 curl -T uploadfile -u user:passwd ftp://ftp.example.com/ 236 237Upload a local file to get appended to the remote file: 238 239 curl -T localfile -a ftp://ftp.example.com/remotefile 240 241Curl also supports ftp upload through a proxy, but only if the proxy is 242configured to allow that kind of tunneling. If it does, you can run curl in a 243fashion similar to: 244 245 curl --proxytunnel -x proxy:port -T localfile ftp.example.com 246 247### SMB / SMBS 248 249 curl -T file.txt -u "domain\username:passwd" 250 smb://server.example.com/share/ 251 252### HTTP 253 254Upload all data on stdin to a specified HTTP site: 255 256 curl -T - http://www.example.com/myfile 257 258Note that the HTTP server must have been configured to accept PUT before this 259can be done successfully. 260 261For other ways to do HTTP data upload, see the POST section below. 262 263## Verbose / Debug 264 265If curl fails where it is not supposed to, if the servers do not let you in, 266if you cannot understand the responses: use the `-v` flag to get verbose 267fetching. Curl outputs lots of info and what it sends and receives in order to 268let the user see all client-server interaction (but it does not show you the 269actual data). 270 271 curl -v ftp://ftp.example.com/ 272 273To get even more details and information on what curl does, try using the 274`--trace` or `--trace-ascii` options with a given filename to log to, like 275this: 276 277 curl --trace trace.txt www.haxx.se 278 279 280## Detailed Information 281 282Different protocols provide different ways of getting detailed information 283about specific files/documents. To get curl to show detailed information about 284a single file, you should use `-I`/`--head` option. It displays all available 285info on a single file for HTTP and FTP. The HTTP information is a lot more 286extensive. 287 288For HTTP, you can get the header information (the same as `-I` would show) 289shown before the data by using `-i`/`--include`. Curl understands the 290`-D`/`--dump-header` option when getting files from both FTP and HTTP, and it 291then stores the headers in the specified file. 292 293Store the HTTP headers in a separate file (headers.txt in the example): 294 295 curl --dump-header headers.txt curl.se 296 297Note that headers stored in a separate file can be useful at a later time if 298you want curl to use cookies sent by the server. More about that in the 299cookies section. 300 301## POST (HTTP) 302 303It is easy to post data using curl. This is done using the `-d <data>` option. 304The post data must be urlencoded. 305 306Post a simple `name` and `phone` guestbook. 307 308 curl -d "name=Rafael%20Sagula&phone=3320780" http://www.example.com/guest.cgi 309 310Or automatically [URL encode the data](https://everything.curl.dev/http/post/url-encode). 311 312 curl --data-urlencode "name=Rafael Sagula&phone=3320780" http://www.example.com/guest.cgi 313 314How to post a form with curl, lesson #1: 315 316Dig out all the `<input>` tags in the form that you want to fill in. 317 318If there is a normal post, you use `-d` to post. `-d` takes a full post 319string, which is in the format 320 321 <variable1>=<data1>&<variable2>=<data2>&... 322 323The variable names are the names set with `"name="` in the `<input>` tags, and 324the data is the contents you want to fill in for the inputs. The data *must* 325be properly URL encoded. That means you replace space with + and that you 326replace weird letters with `%XX` where `XX` is the hexadecimal representation 327of the letter's ASCII code. 328 329Example: 330 331(say if `http://example.com` had the following html) 332 333```html 334<form action="post.cgi" method="post"> 335 <input name=user size=10> 336 <input name=pass type=password size=10> 337 <input name=id type=hidden value="blablabla"> 338 <input name=ding value="submit"> 339</form> 340``` 341 342We want to enter user `foobar` with password `12345`. 343 344To post to this, you would enter a curl command line like: 345 346 curl -d "user=foobar&pass=12345&id=blablabla&ding=submit" http://example.com/post.cgi 347 348While `-d` uses the application/x-www-form-urlencoded mime-type, generally 349understood by CGI's and similar, curl also supports the more capable 350multipart/form-data type. This latter type supports things like file upload. 351 352`-F` accepts parameters like `-F "name=contents"`. If you want the contents to 353be read from a file, use `@filename` as contents. When specifying a file, you 354can also specify the file content type by appending `;type=<mime type>` to the 355filename. You can also post the contents of several files in one field. For 356example, the field name `coolfiles` is used to send three files, with 357different content types using the following syntax: 358 359 curl -F "coolfiles=@fil1.gif;type=image/gif,fil2.txt,fil3.html" 360 http://www.example.com/postit.cgi 361 362If the content-type is not specified, curl tries to guess from the file 363extension (it only knows a few), or use the previously specified type (from an 364earlier file if several files are specified in a list) or else it uses the 365default type `application/octet-stream`. 366 367Emulate a fill-in form with `-F`. Let's say you fill in three fields in a 368form. One field is a filename which to post, one field is your name and one 369field is a file description. We want to post the file we have written named 370`cooltext.txt`. To let curl do the posting of this data instead of your 371favorite browser, you have to read the HTML source of the form page and find 372the names of the input fields. In our example, the input field names are 373`file`, `yourname` and `filedescription`. 374 375 curl -F "file=@cooltext.txt" -F "yourname=Daniel" 376 -F "filedescription=Cool text file with cool text inside" 377 http://www.example.com/postit.cgi 378 379To send two files in one post you can do it in two ways: 380 381Send multiple files in a single field with a single field name: 382 383 curl -F "pictures=@dog.gif,cat.gif" $URL 384 385Send two fields with two field names 386 387 curl -F "docpicture=@dog.gif" -F "catpicture=@cat.gif" $URL 388 389To send a field value literally without interpreting a leading `@` or `<`, or 390an embedded `;type=`, use `--form-string` instead of `-F`. This is recommended 391when the value is obtained from a user or some other unpredictable 392source. Under these circumstances, using `-F` instead of `--form-string` could 393allow a user to trick curl into uploading a file. 394 395## Referrer 396 397An HTTP request has the option to include information about which address 398referred it to the actual page. curl allows you to specify the referrer to be 399used on the command line. It is especially useful to fool or trick stupid 400servers or CGI scripts that rely on that information being available or 401contain certain data. 402 403 curl -e www.example.org http://www.example.com/ 404 405## User Agent 406 407An HTTP request has the option to include information about the browser that 408generated the request. Curl allows it to be specified on the command line. It 409is especially useful to fool or trick stupid servers or CGI scripts that only 410accept certain browsers. 411 412Example: 413 414 curl -A 'Mozilla/3.0 (Win95; I)' http://www.bank.example.com/ 415 416Other common strings: 417 418- `Mozilla/3.0 (Win95; I)` - Netscape Version 3 for Windows 95 419- `Mozilla/3.04 (Win95; U)` - Netscape Version 3 for Windows 95 420- `Mozilla/2.02 (OS/2; U)` - Netscape Version 2 for OS/2 421- `Mozilla/4.04 [en] (X11; U; AIX 4.2; Nav)` - Netscape for AIX 422- `Mozilla/4.05 [en] (X11; U; Linux 2.0.32 i586)` - Netscape for Linux 423 424Note that Internet Explorer tries hard to be compatible in every way: 425 426- `Mozilla/4.0 (compatible; MSIE 4.01; Windows 95)` - MSIE for W95 427 428Mozilla is not the only possible User-Agent name: 429 430- `Konqueror/1.0` - KDE File Manager desktop client 431- `Lynx/2.7.1 libwww-FM/2.14` - Lynx command line browser 432 433## Cookies 434 435Cookies are generally used by web servers to keep state information at the 436client's side. The server sets cookies by sending a response line in the 437headers that looks like `Set-Cookie: <data>` where the data part then 438typically contains a set of `NAME=VALUE` pairs (separated by semicolons `;` 439like `NAME1=VALUE1; NAME2=VALUE2;`). The server can also specify for what path 440the cookie should be used for (by specifying `path=value`), when the cookie 441should expire (`expire=DATE`), for what domain to use it (`domain=NAME`) and 442if it should be used on secure connections only (`secure`). 443 444If you have received a page from a server that contains a header like: 445 446```http 447Set-Cookie: sessionid=boo123; path="/foo"; 448``` 449 450it means the server wants that first pair passed on when we get anything in a 451path beginning with `/foo`. 452 453Example, get a page that wants my name passed in a cookie: 454 455 curl -b "name=Daniel" www.example.com 456 457Curl also has the ability to use previously received cookies in following 458sessions. If you get cookies from a server and store them in a file in a 459manner similar to: 460 461 curl --dump-header headers www.example.com 462 463... you can then in a second connect to that (or another) site, use the 464cookies from the `headers.txt` file like: 465 466 curl -b headers.txt www.example.com 467 468While saving headers to a file is a working way to store cookies, it is 469however error-prone and not the preferred way to do this. Instead, make curl 470save the incoming cookies using the well-known Netscape cookie format like 471this: 472 473 curl -c cookies.txt www.example.com 474 475Note that by specifying `-b` you enable the cookie engine and with `-L` you 476can make curl follow a `location:` (which often is used in combination with 477cookies). If a site sends cookies and a location field, you can use a 478non-existing file to trigger the cookie awareness like: 479 480 curl -L -b empty.txt www.example.com 481 482The file to read cookies from must be formatted using plain HTTP headers OR as 483Netscape's cookie file. Curl determines what kind it is based on the file 484contents. In the above command, curl parses the header and store the cookies 485received from www.example.com. curl sends the stored cookies which match the 486request to the server as it follows the location. The file `empty.txt` may be 487a nonexistent file. 488 489To read and write cookies from a Netscape cookie file, you can set both `-b` 490and `-c` to use the same file: 491 492 curl -b cookies.txt -c cookies.txt www.example.com 493 494## Progress Meter 495 496The progress meter exists to show a user that something actually is 497happening. The different fields in the output have the following meaning: 498 499 % Total % Received % Xferd Average Speed Time Curr. 500 Dload Upload Total Current Left Speed 501 0 151M 0 38608 0 0 9406 0 4:41:43 0:00:04 4:41:39 9287 502 503From left-to-right: 504 505 - `%` - percentage completed of the whole transfer 506 - `Total` - total size of the whole expected transfer 507 - `%` - percentage completed of the download 508 - `Received` - currently downloaded amount of bytes 509 - `%` - percentage completed of the upload 510 - `Xferd` - currently uploaded amount of bytes 511 - `Average Speed Dload` - the average transfer speed of the download 512 - `Average Speed Upload` - the average transfer speed of the upload 513 - `Time Total` - expected time to complete the operation 514 - `Time Current` - time passed since the invoke 515 - `Time Left` - expected time left to completion 516 - `Curr.Speed` - the average transfer speed the last 5 seconds (the first 517 5 seconds of a transfer is based on less time of course.) 518 519The `-#` option displays a totally different progress bar that does not need 520much explanation! 521 522## Speed Limit 523 524Curl allows the user to set the transfer speed conditions that must be met to 525let the transfer keep going. By using the switch `-y` and `-Y` you can make 526curl abort transfers if the transfer speed is below the specified lowest limit 527for a specified time. 528 529To have curl abort the download if the speed is slower than 3000 bytes per 530second for 1 minute, run: 531 532 curl -Y 3000 -y 60 www.far-away.example.com 533 534This can be used in combination with the overall time limit, so that the above 535operation must be completed in whole within 30 minutes: 536 537 curl -m 1800 -Y 3000 -y 60 www.far-away.example.com 538 539Forcing curl not to transfer data faster than a given rate is also possible, 540which might be useful if you are using a limited bandwidth connection and you 541do not want your transfer to use all of it (sometimes referred to as 542*bandwidth throttle*). 543 544Make curl transfer data no faster than 10 kilobytes per second: 545 546 curl --limit-rate 10K www.far-away.example.com 547 548or 549 550 curl --limit-rate 10240 www.far-away.example.com 551 552Or prevent curl from uploading data faster than 1 megabyte per second: 553 554 curl -T upload --limit-rate 1M ftp://uploads.example.com 555 556When using the `--limit-rate` option, the transfer rate is regulated on a 557per-second basis, which causes the total transfer speed to become lower than 558the given number. Sometimes of course substantially lower, if your transfer 559stalls during periods. 560 561## Config File 562 563Curl automatically tries to read the `.curlrc` file (or `_curlrc` file on 564Microsoft Windows systems) from the user's home directory on startup. 565 566The config file could be made up with normal command line switches, but you 567can also specify the long options without the dashes to make it more 568readable. You can separate the options and the parameter with spaces, or with 569`=` or `:`. Comments can be used within the file. If the first letter on a 570line is a `#`-symbol the rest of the line is treated as a comment. 571 572If you want the parameter to contain spaces, you must enclose the entire 573parameter within double quotes (`"`). Within those quotes, you specify a quote 574as `\"`. 575 576NOTE: You must specify options and their arguments on the same line. 577 578Example, set default time out and proxy in a config file: 579 580 # We want a 30 minute timeout: 581 -m 1800 582 # ... and we use a proxy for all accesses: 583 proxy = proxy.our.domain.com:8080 584 585Whitespaces ARE significant at the end of lines, but all whitespace leading 586up to the first characters of each line are ignored. 587 588Prevent curl from reading the default file by using -q as the first command 589line parameter, like: 590 591 curl -q www.example.org 592 593Force curl to get and display a local help page in case it is invoked without 594URL by making a config file similar to: 595 596 # default url to get 597 url = "http://help.with.curl.example.com/curlhelp.html" 598 599You can specify another config file to be read by using the `-K`/`--config` 600flag. If you set config filename to `-` it reads the config from stdin, which 601can be handy if you want to hide options from being visible in process tables 602etc: 603 604 echo "user = user:passwd" | curl -K - http://that.secret.example.com 605 606## Extra Headers 607 608When using curl in your own programs, you may end up needing to pass on your 609own custom headers when getting a webpage. You can do this by using the `-H` 610flag. 611 612Example, send the header `X-you-and-me: yes` to the server when getting a 613page: 614 615 curl -H "X-you-and-me: yes" love.example.com 616 617This can also be useful in case you want curl to send a different text in a 618header than it normally does. The `-H` header you specify then replaces the 619header curl would normally send. If you replace an internal header with an 620empty one, you prevent that header from being sent. To prevent the `Host:` 621header from being used: 622 623 curl -H "Host:" server.example.com 624 625## FTP and Path Names 626 627Do note that when getting files with a `ftp://` URL, the given path is 628relative to the directory you enter. To get the file `README` from your home 629directory at your ftp site, do: 630 631 curl ftp://user:passwd@my.example.com/README 632 633If you want the README file from the root directory of that same site, you 634need to specify the absolute filename: 635 636 curl ftp://user:passwd@my.example.com//README 637 638(I.e with an extra slash in front of the filename.) 639 640## SFTP and SCP and Path Names 641 642With sftp: and scp: URLs, the path name given is the absolute name on the 643server. To access a file relative to the remote user's home directory, prefix 644the file with `/~/` , such as: 645 646 curl -u $USER sftp://home.example.com/~/.bashrc 647 648## FTP and Firewalls 649 650The FTP protocol requires one of the involved parties to open a second 651connection as soon as data is about to get transferred. There are two ways to 652do this. 653 654The default way for curl is to issue the PASV command which causes the server 655to open another port and await another connection performed by the 656client. This is good if the client is behind a firewall that does not allow 657incoming connections. 658 659 curl ftp.example.com 660 661If the server, for example, is behind a firewall that does not allow 662connections on ports other than 21 (or if it just does not support the `PASV` 663command), the other way to do it is to use the `PORT` command and instruct the 664server to connect to the client on the given IP number and port (as parameters 665to the PORT command). 666 667The `-P` flag to curl supports a few different options. Your machine may have 668several IP-addresses and/or network interfaces and curl allows you to select 669which of them to use. Default address can also be used: 670 671 curl -P - ftp.example.com 672 673Download with `PORT` but use the IP address of our `le0` interface (this does 674not work on Windows): 675 676 curl -P le0 ftp.example.com 677 678Download with `PORT` but use 192.168.0.10 as our IP address to use: 679 680 curl -P 192.168.0.10 ftp.example.com 681 682## Network Interface 683 684Get a webpage from a server using a specified port for the interface: 685 686 curl --interface eth0:1 http://www.example.com/ 687 688or 689 690 curl --interface 192.168.1.10 http://www.example.com/ 691 692## HTTPS 693 694Secure HTTP requires a TLS library to be installed and used when curl is 695built. If that is done, curl is capable of retrieving and posting documents 696using the HTTPS protocol. 697 698Example: 699 700 curl https://secure.example.com 701 702curl is also capable of using client certificates to get/post files from sites 703that require valid certificates. The only drawback is that the certificate 704needs to be in PEM-format. PEM is a standard and open format to store 705certificates with, but it is not used by the most commonly used browsers. If 706you want curl to use the certificates you use with your favorite browser, you 707may need to download/compile a converter that can convert your browser's 708formatted certificates to PEM formatted ones. 709 710Example on how to automatically retrieve a document using a certificate with a 711personal password: 712 713 curl -E /path/to/cert.pem:password https://secure.example.com/ 714 715If you neglect to specify the password on the command line, you are prompted 716for the correct password before any data can be received. 717 718Many older HTTPS servers have problems with specific SSL or TLS versions, 719which newer versions of OpenSSL etc use, therefore it is sometimes useful to 720specify what TLS version curl should use.: 721 722 curl --tlv1.0 https://secure.example.com/ 723 724Otherwise, curl attempts to use a sensible TLS default version. 725 726## Resuming File Transfers 727 728To continue a file transfer where it was previously aborted, curl supports 729resume on HTTP(S) downloads as well as FTP uploads and downloads. 730 731Continue downloading a document: 732 733 curl -C - -o file ftp://ftp.example.com/path/file 734 735Continue uploading a document: 736 737 curl -C - -T file ftp://ftp.example.com/path/file 738 739Continue downloading a document from a web server 740 741 curl -C - -o file http://www.example.com/ 742 743## Time Conditions 744 745HTTP allows a client to specify a time condition for the document it requests. 746It is `If-Modified-Since` or `If-Unmodified-Since`. curl allows you to specify 747them with the `-z`/`--time-cond` flag. 748 749For example, you can easily make a download that only gets performed if the 750remote file is newer than a local copy. It would be made like: 751 752 curl -z local.html http://remote.example.com/remote.html 753 754Or you can download a file only if the local file is newer than the remote 755one. Do this by prepending the date string with a `-`, as in: 756 757 curl -z -local.html http://remote.example.com/remote.html 758 759You can specify a plain text date as condition. Tell curl to only download the 760file if it was updated since January 12, 2012: 761 762 curl -z "Jan 12 2012" http://remote.example.com/remote.html 763 764curl accepts a wide range of date formats. You always make the date check the 765other way around by prepending it with a dash (`-`). 766 767## DICT 768 769For fun try 770 771 curl dict://dict.org/m:curl 772 curl dict://dict.org/d:heisenbug:jargon 773 curl dict://dict.org/d:daniel:gcide 774 775Aliases for `m` are `match` and `find`, and aliases for `d` are `define` and 776`lookup`. For example, 777 778 curl dict://dict.org/find:curl 779 780Commands that break the URL description of the RFC (but not the DICT 781protocol) are 782 783 curl dict://dict.org/show:db 784 curl dict://dict.org/show:strat 785 786Authentication support is still missing 787 788## LDAP 789 790If you have installed the OpenLDAP library, curl can take advantage of it and 791offer `ldap://` support. On Windows, curl uses WinLDAP from Platform SDK by 792default. 793 794Default protocol version used by curl is LDAP version 3. Version 2 is used as 795a fallback mechanism in case version 3 fails to connect. 796 797LDAP is a complex thing and writing an LDAP query is not an easy 798task. Familiarize yourself with the exact syntax description elsewhere. One 799such place might be: [RFC 2255, The LDAP URL 800Format](https://curl.se/rfc/rfc2255.txt) 801 802To show you an example, this is how to get all people from an LDAP server that 803has a certain subdomain in their email address: 804 805 curl -B "ldap://ldap.example.com/o=frontec??sub?mail=*sth.example.com" 806 807You also can use authentication when accessing LDAP catalog: 808 809 curl -u user:passwd "ldap://ldap.example.com/o=frontec??sub?mail=*" 810 curl "ldap://user:passwd@ldap.example.com/o=frontec??sub?mail=*" 811 812By default, if user and password are provided, OpenLDAP/WinLDAP uses basic 813authentication. On Windows you can control this behavior by providing one of 814`--basic`, `--ntlm` or `--digest` option in curl command line 815 816 curl --ntlm "ldap://user:passwd@ldap.example.com/o=frontec??sub?mail=*" 817 818On Windows, if no user/password specified, auto-negotiation mechanism is used 819with current logon credentials (SSPI/SPNEGO). 820 821## Environment Variables 822 823Curl reads and understands the following environment variables: 824 825 http_proxy, HTTPS_PROXY, FTP_PROXY 826 827They should be set for protocol-specific proxies. General proxy should be set 828with 829 830 ALL_PROXY 831 832A comma-separated list of hostnames that should not go through any proxy is 833set in (only an asterisk, `*` matches all hosts) 834 835 NO_PROXY 836 837If the hostname matches one of these strings, or the host is within the domain 838of one of these strings, transactions with that node is not done over the 839proxy. When a domain is used, it needs to start with a period. A user can 840specify that both www.example.com and foo.example.com should not use a proxy 841by setting `NO_PROXY` to `.example.com`. By including the full name you can 842exclude specific hostnames, so to make `www.example.com` not use a proxy but 843still have `foo.example.com` do it, set `NO_PROXY` to `www.example.com`. 844 845The usage of the `-x`/`--proxy` flag overrides the environment variables. 846 847## Netrc 848 849Unix introduced the `.netrc` concept a long time ago. It is a way for a user 850to specify name and password for commonly visited FTP sites in a file so that 851you do not have to type them in each time you visit those sites. You realize 852this is a big security risk if someone else gets hold of your passwords, 853therefore most Unix programs do not read this file unless it is only readable 854by yourself (curl does not care though). 855 856Curl supports `.netrc` files if told to (using the `-n`/`--netrc` and 857`--netrc-optional` options). This is not restricted to just FTP, so curl can 858use it for all protocols where authentication is used. 859 860A simple `.netrc` file could look something like: 861 862 machine curl.se login iamdaniel password mysecret 863 864## Custom Output 865 866To better allow script programmers to get to know about the progress of curl, 867the `-w`/`--write-out` option was introduced. Using this, you can specify what 868information from the previous transfer you want to extract. 869 870To display the amount of bytes downloaded together with some text and an 871ending newline: 872 873 curl -w 'We downloaded %{size_download} bytes\n' www.example.com 874 875## Kerberos FTP Transfer 876 877Curl supports kerberos4 and kerberos5/GSSAPI for FTP transfers. You need the 878kerberos package installed and used at curl build time for it to be available. 879 880First, get the krb-ticket the normal way, like with the `kinit`/`kauth` tool. 881Then use curl in way similar to: 882 883 curl --krb private ftp://krb4site.example.com -u username:fakepwd 884 885There is no use for a password on the `-u` switch, but a blank one makes curl 886ask for one and you already entered the real password to `kinit`/`kauth`. 887 888## TELNET 889 890The curl telnet support is basic and easy to use. Curl passes all data passed 891to it on stdin to the remote server. Connect to a remote telnet server using a 892command line similar to: 893 894 curl telnet://remote.example.com 895 896Enter the data to pass to the server on stdin. The result is sent to stdout or 897to the file you specify with `-o`. 898 899You might want the `-N`/`--no-buffer` option to switch off the buffered output 900for slow connections or similar. 901 902Pass options to the telnet protocol negotiation, by using the `-t` option. To 903tell the server we use a vt100 terminal, try something like: 904 905 curl -tTTYPE=vt100 telnet://remote.example.com 906 907Other interesting options for it `-t` include: 908 909 - `XDISPLOC=<X display>` Sets the X display location. 910 - `NEW_ENV=<var,val>` Sets an environment variable. 911 912NOTE: The telnet protocol does not specify any way to login with a specified 913user and password so curl cannot do that automatically. To do that, you need to 914track when the login prompt is received and send the username and password 915accordingly. 916 917## Persistent Connections 918 919Specifying multiple files on a single command line makes curl transfer all of 920them, one after the other in the specified order. 921 922libcurl attempts to use persistent connections for the transfers so that the 923second transfer to the same host can use the same connection that was already 924initiated and was left open in the previous transfer. This greatly decreases 925connection time for all but the first transfer and it makes a far better use 926of the network. 927 928Note that curl cannot use persistent connections for transfers that are used 929in subsequent curl invokes. Try to stuff as many URLs as possible on the same 930command line if they are using the same host, as that makes the transfers 931faster. If you use an HTTP proxy for file transfers, practically all transfers 932are persistent. 933 934## Multiple Transfers With A Single Command Line 935 936As is mentioned above, you can download multiple files with one command line 937by simply adding more URLs. If you want those to get saved to a local file 938instead of just printed to stdout, you need to add one save option for each 939URL you specify. Note that this also goes for the `-O` option (but not 940`--remote-name-all`). 941 942For example: get two files and use `-O` for the first and a custom file 943name for the second: 944 945 curl -O http://example.com/file.txt ftp://example.com/moo.exe -o moo.jpg 946 947You can also upload multiple files in a similar fashion: 948 949 curl -T local1 ftp://example.com/moo.exe -T local2 ftp://example.com/moo2.txt 950 951## IPv6 952 953curl connects to a server with IPv6 when a host lookup returns an IPv6 address 954and fall back to IPv4 if the connection fails. The `--ipv4` and `--ipv6` 955options can specify which address to use when both are available. IPv6 956addresses can also be specified directly in URLs using the syntax: 957 958 http://[2001:1890:1112:1::20]/overview.html 959 960When this style is used, the `-g` option must be given to stop curl from 961interpreting the square brackets as special globbing characters. Link local 962and site local addresses including a scope identifier, such as `fe80::1234%1`, 963may also be used, but the scope portion must be numeric or match an existing 964network interface on Linux and the percent character must be URL escaped. The 965previous example in an SFTP URL might look like: 966 967 sftp://[fe80::1234%251]/ 968 969IPv6 addresses provided other than in URLs (e.g. to the `--proxy`, 970`--interface` or `--ftp-port` options) should not be URL encoded. 971 972## Mailing Lists 973 974For your convenience, we have several open mailing lists to discuss curl, its 975development and things relevant to this. Get all info at 976https://curl.se/mail/. 977 978Please direct curl questions, feature requests and trouble reports to one of 979these mailing lists instead of mailing any individual. 980 981Available lists include: 982 983### `curl-users` 984 985Users of the command line tool. How to use it, what does not work, new 986features, related tools, questions, news, installations, compilations, 987running, porting etc. 988 989### `curl-library` 990 991Developers using or developing libcurl. Bugs, extensions, improvements. 992 993### `curl-announce` 994 995Low-traffic. Only receives announcements of new public versions. At worst, 996that makes something like one or two mails per month, but usually only one 997mail every second month. 998 999### `curl-and-php` 1000 1001Using the curl functions in PHP. Everything curl with a PHP angle. Or PHP with 1002a curl angle. 1003 1004### `curl-and-python` 1005 1006Python hackers using curl with or without the python binding pycurl. 1007