command line variables
idea brain-storming area
--expand- is a new prefix for options on the command line and in config
files. If this prefix is used to a command line option, it means that the
value allows for variable expansion.
When expanding variables, the syntax to expand them is with {{name}} that
then inserts the contents of the specific variable instead. The expansion can
also insert an environment variable using the extended syntax {{env:name}}.
If no expansion is performed for a --expand- option, a warning will be
displayed.
Example, expanding the curl variable foo and the environment variable USER:
--expand-url "https://example.org/{{foo}}/{{env:USER}}"
The command line option --variable [name=data/@file] sets internal curl variables
to have names with contents. This option can be used on the command line and
in config files of course, any number of times.
This option is order-sensitive in that it has a meaning on where in the chain of options it is placed on the command line or config file. It sets the variable content at that point in the command line and will then be set for the following options.
The variable option itself can be expanded if used with a --expand- prefix.
Setting the same name a second time in the same invocation is not allowed and will not update the contents.
A variable name consists only of the characters "a-zA-Z0-9_", and may not be longer than 128 bytes.
The data for a variable can be provided different ways:
Specifies that exact data in a string.
The data will be read from the given file name.
The data will be read from stdin.
To help creating better command lines, there are "functions" that can be applied to the contents when a variable is expanded.
The functions are specified after the variable name, separated by a colon (:). There can be one or more functions applied to a variable. The functions are applied in a left-to-right order.
Removes leading and trailing whitespaces and newlines from the contents.
{{foo:trim}}
Expands the string with JSON escape sequences
{{foo:json}}
Percent-encodes the entire contents.
Example: an environment variable that is trimmed and percent-encoded:
{{env:HOME:trim:percent}}
Get the contents from the file "$HOME/.file" and use it as a directory name when requesting a URL, add the user name as a file name.
curl \
--expand-variable foo@{{env:HOME}}/.file \
--expand-url "https://example.org/{{foo:%}}/{{env:USER:%}}"
Pass a secret key to curl via a pipe.
printf %s "$secret" |
curl -g \
--variable secret@- \
--expand-url 'https:/example.org/{{secret:%}}/method'
Make JSON request using the content of a shell variable in the payload.
curl \
--variable "query=$query" \
--expand-json '{ "query": "{{query:json}}", "searchType": "all" }' \
https://example.org/api/search