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Bash Script to Generate Config or Property Files From a Template File Containing Variables

Here's a quick way to set up a Bash script when dealing with a template file containing variables.

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Sometimes, we have configuration or properties file (as templates) such as httpd.conf or server.conf where we want to dynamically replace $variables with values before writing the output to a new file.

Example:

# httpd.conf.tmpl
<Location $STATUS_URI>
    SetHandler server-status
    Order deny,allow
    Deny from all
    Allow from $MONITOR_IP
</Location>


We want to develop an install script in Bash such that it reads the httpd.conf.tmpl and replaces the $STATUS_URI and $MONITOR_IP with appropriate values (either passed in as script arguments or coded in the bash script) and then write out the resulting output to a new file, such as /tmp/httpd.conf.

Here is such as script:

#!/usr/bin/env bash

# Define the variables with values you want replaced
STATUS_URI="foobar"
MONITOR_IP="192.168.1.1"
# This could also be read in via bash arguments. 
# Google "bash getopts" for more information

# render a template configuration file
# expand variables + preserve formatting
# user="Venkatt"
# referenced inside the template.txt as $user
# render_template /path/to/template.txt > path/to/configuration_file
function render_template() {
  eval "echo \"$(cat $1)\""
}

function generate_httpd_conf {
  echo "#### Creating /tmp/httpd.conf from template ./httpd.conf.tmpl"
  render_template httpd.conf.tmpl > /tmp/httpd.conf
}


Generated output:

<Location foobar>
    SetHandler server-status
    Order deny,allow
    Deny from all
    Allow from 192.168.1.1
</Location>


This can be a useful method to generate .conf .prop (configuration or properties) files.

Cheers.

And now for today’s inspirational quote:

Let us sacrifice our today so that our children can have a better tomorrow.
 – Abdul Kalam
 – 11th President of India from 2002 to 2007
 – Chief ‘Rocket’ Scientist born from a poor family with humble beginnings.
 – Lived as a “Man of simplicity”

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Topics:
variables ,configuration ,values ,templates ,properties

Published at DZone with permission of Venkatt Guhesan, DZone MVB. See the original article here.

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