Next: , Previous: , Up: sh   [Contents][Index] Invoking the envsubst program

envsubst [option] [shell-format]

The envsubst program substitutes the values of environment variables.

Operation mode


Output the variables occurring in shell-format.

Informative output


Display this help and exit.


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.