envsubst --version (return code: 0)
envsubst (GNU gettext-runtime) 0.19.7
Copyright (C) 2003-2007 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Written by Bruno Haible.
envsubst --help (return code: 0)
Usage: envsubst [OPTION] [SHELL-FORMAT]
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.
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.
Report bugs to <bug-gnu-gettext@gnu.org>.