Bash/Sh As A Template Engine

As part of a shell script, I wanted to generate a configuration file based on a template. At first, I thought I would use some sort of cat and sed combo or an awk program. Then I realized Bash/Sh have everything needed builtin.

Considering the following template file:

Username: ${user}

And the following shell script:

#!/bin/sh

# render a template configuration file
# expand variables + preserve formatting
render_template() {
  eval "echo \"$(cat $1)\""
}

user="Gregory"
render_template /path/to/template.txt > path/to/configuration_file

The call to the render_template helper will replace ${user} with “Gregory” in the template, keeping formatting.