envsubst

Substitutes environment variables with their value in shell format strings. Variables to be replaced should be in either ${var} or $var format. More information: https://www.gnu.org/software/gettext/manual/html_node/envsubst-Invocation.html.

• Replace environment variables in stdin and output to stdout:

echo '$HOME' | envsubst

• Replace environment variables in an input file and output to stdout:

envsubst < path/to/input_file

• Replace environment variables in an input file and output to a file:

envsubst < path/to/input_file > path/to/output_file

• Replace environment variables in an input file from a space-separated list:

envsubst '$USER $SHELL $HOME' < path/to/input_file