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.