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envsubst
programenvsubst [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.