c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Long: variable
Arg: <[%]name=text/@file>
Help: Set variable
Category: curl
Example: --variable name=smith $URL
Added: 8.3.0
See-also: config
Multi: append
---
Set a variable with "name=content" or "name@file" (where "file" can be stdin
if set to a single dash (-)). The name is a case sensitive identifier that
must consist of no other letters than a-z, A-Z, 0-9 or underscore. The
specified content is then associated with this identifier.

The name must be unique within a command line invoke, setting the same
variable name again will be ignored.

The contents of a variable can be referenced in a later command line option
when that option name is prefixed with "--expand-", and the name is used as
"{{name}}" (without the quotes).

--variable can import environment variables into the name space. Opt to either
require the environment variable to be set or provide a default value for the
variable in case it is not already set.

--variable %name imports the variable called 'name' but exits with an error if
that environment variable is not alreadty set. To provide a default value if
the environment variable is not set, use --variable %name=content or
--variable %name@content. Note that on some systems - but not all -
environment variables are case insensitive.

When expanding variables, curl supports a set of functions that can make the
variable contents more convenient to use. You apply a function to a variable
expansion by adding a colon and then list the desired functions in a
comma-separted list that is evaluated in a left-to-right order. Variable
content holding null bytes that are not encoded when expanded, will cause
error.

These are functions that can help you get the value inserted more
conveniently.

"trim" removes all leading and trailing white space.

"json" outputs the content using JSON string quoting rules.

"url" shows the content URL (percent) encoded.

"b64" expands the variable base64 encoded