how to print content of a file with environmental variables interpreted This question is similar to this one: Is it possible to print the content of the content of a variable with shell script? (indirect referencing) In a file that is a=${env1}is a good ${env2} b=${env3}is a good ${env2} I would like to show content of this file to: a=tom is a good cat b=jerry is a good mouse I tried this: tmp=`cat a.conf` echo $tmp # environmental variables are not interpreted, and file format changed, hard to read echo ${!tmp} # no ... Besides, above idea is kinda detour.

If you have a file that looks like this:


a=${env1} is a good ${env2}
b=${env3} is a good ${env4}


And you want to produce output with the variables substituted, you use the `envsubst` command, which is part of the `gettext` package. Assuming the above is in `example.txt.in`, we could run:


env1=tom env2=cat env3=jerry env4=mouse envsubst < example.txt.in


And get as output:


a=tom is a good cat
b=jerry is a good mouse


* * *

If `ensubst` isn't available, you could do something like:


#!/bin/sh

tmpfile=$(mktemp scriptXXXXXX)
trap 'rm -f $tmpfile' EXIT

cat > "$tmpfile" < cat < $(cat)
END_INSIDE
END_OUTSIDE

sh "$tmpfile"


Name the script something like `envsubst.sh`, and run it similarly to the previous example:

`env1=tom env2=cat env3=jerry env4=mouse sh envsubst.sh < example.txt.in`