GNU gettext utilities: envsubst Invocation
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15.5.12.5 Invoking the envsubst program
envsubst [option] [shell-format]
The envsubst program substitutes the values of environment variables.
Operation mode
- ‘
-v’
‘--variables’ Output the variables occurring in
shell-format.
Informative output
- ‘
-h’
‘--help’ Display this help and exit.
- ‘
-V’
‘--version’ Output version information and exit.
In normal operation mode, standard input is copied to standard output, with references to environment variables of the form $VARIABLE or ${VARIABLE} being replaced with the corresponding values. If a shell-format is given, only those environment variables that are referenced in shell-format are substituted; otherwise all environment variables references occurring in standard input are substituted.
These substitutions are a subset of the substitutions that a shell performs on unquoted and double-quoted strings. Other kinds of substitutions done by a shell, such as ${variable-default} or $(command-list) or `command-list`, are not performed by the envsubst program, due to security reasons.
When --variables is used, standard input is ignored, and the output consists of the environment variables that are referenced in shell-format, one per line.
