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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
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.