How to include a template.tmpl as a here-doc of a script

Question

I have a template file(template.tmpl):

Hello, $x
Hello, $y

I have a script file(variables.sh):

#!/bin/bash
x=foo
y=bar
# I want to include template.tmpl as a here-doc

How to include template.tmpl as a here-doc of variables.sh.
So that, the rendered output should be:

Hello, foo
Hello, bar

---

Edit: (in 2012)

I think replace is a good command for my job：

$ cat template.tmpl | replace '$x' foo '$y' bar

A more sophisticated tool:

$ cheetah compile template.tmpl
$ x=foo y=bar python template.py --env

---

Edit: (in 2024)

Maybe envsubst is the tool I should try:

set -o allexport
source variables.sh
set +o allexport
envsubst < template.tmpl

Answer 1

I use this function in one of my projects. It builds an actual here document from the template and then executes it in the current shell using .:

# usage: apply_template /path/to/template.txt
apply_template () {
        (
        trap 'rm -f $tempfile' EXIT
        tempfile=$(mktemp $(pwd)/templateXXXXXX)

        echo 'cat <<END_TEMPLATE' > $tempfile
        cat $1 >> $tempfile
        echo END_TEMPLATE >> $tempfile

        . $tempfile
        )
}