     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.