How do you create a custom function in Puppet?

To create a custom function in Puppet, the correct method involves adding Ruby files in the specified directory structure: <modulepath>/<modulename>/lib/puppet/parser/functions. This is the standard approach that Puppet uses for defining custom functions. By placing the Ruby files in this directory, you ensure that Puppet recognizes and loads them as functions that can be called from Puppet manifests.

These functions can encapsulate reusable logic that can be invoked with certain parameters, allowing for greater modularity and maintainability of Puppet code. The use of Ruby for custom functions makes them powerful as you can leverage Ruby's capabilities to perform complex operations and data manipulations.

The other options do not align with the correct methodology for defining custom functions in Puppet. Writing a Puppet script and executing it with the Puppet agent does not directly create a reusable function in the manner that is typical for Puppet modules. Including the function inside the main Puppet manifest would also not define a custom function that is reusable across multiple manifests. Finally, creating a module with predefined functions only might limit functionality and does not adhere to the need for custom logic to be implemented through Ruby files in the specified directory.