# VARIABLES curl supports command line variables (added in 8.3.0). Set variables with --variable name=content or --variable name@file (where `file` can be stdin if set to a single dash (-)). Variable contents can be expanded in option parameters using `{{name}}` if the option name is prefixed with `--expand-`. This gets the contents of the variable `name` inserted, or a blank if the name does not exist as a variable. Insert `{{` verbatim in the string by prefixing it with a backslash, like `\{{`. You access and expand environment variables by first importing them. You select to either require the environment variable to be set or you can provide a default value in case it is not already set. Plain `--variable %name` imports the variable called `name` but exits with an error if that environment variable is not already set. To provide a default value if it is not set, use `--variable %name=content` or `--variable %name@content`. Example. Get the USER environment variable into the URL, fail if USER is not set: --variable '%USER' --expand-url = "https://example.com/api/{{USER}}/method" When expanding variables, curl supports a set of functions that can make the variable contents more convenient to use. It can trim leading and trailing white space with `trim`, it can output the contents as a JSON quoted string with `json`, URL encode the string with `url` or base64 encode it with `b64`. To apply functions to a variable expansion, add them colon separated to the right side of the variable. Variable content holding null bytes that are not encoded when expanded cause error. Example: get the contents of a file called $HOME/.secret into a variable called "fix". Make sure that the content is trimmed and percent-encoded when sent as POST data: --variable %HOME --expand-variable fix@{{HOME}}/.secret --expand-data "{{fix:trim:url}}" https://example.com/ Command line variables and expansions were added in 8.3.0.