Using regular expression substitutions

Puppet's regsubst function provides an easy way to manipulate text, search and replace within strings, or extract patterns from strings. We often need to do this with data obtained from a fact, for example, or from external programs.

In this example, we'll see how to use regsubst to extract the first three octets of an IPv4 address (the network part, assuming it's a class C address).

How to do it…

Follow these steps to build the example:

1. Add the following code to your manifest:

   $class_c = regsubst($::ipaddress, '(.*)\..*', '\1.0')
   notify { "The network part of ${::ipaddress} is
     ${class_c}": }

2. Run Puppet:

   ubuntu@cookbook:~/puppet$ papply
   Notice: The network part of 10.96.247.132 is 10.96.247.0
   Notice: /Stage[main]/Admin::Test/Notify[The network part of 10.96.247.132 is 10.96.247.0]/message: defined 'message' as 'The 
   etwork part of 10.96.247.132 is 10.96.247.0'
   Notice: Finished catalog run in 0.09 seconds
   

How it works…

regsubst takes at least three parameters...