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# Guide to Perl in cPanel - Custom Modules

## Introduction

cPanel & WHM servers include multiple Perl environments. Your Perl modules can use these Perl environments, but they may require certain modifications in order to function correctly.

* For instructions to write your own Perl modules or UAPI functions, read our [Custom UAPI Modules](https://api.docs.cpanel.net/cpanel/introduction) documentation.
* In some cases, you may need to modify a Perl script's shebang line. For more information, read our [Modules and Scripts](/guides/guide-to-perl/guide-to-perl-in-cpanel-modules-and-scripts) documentation.


## Custom modules that ship with WHM

Warning:
Our upgrades to Perl may break custom code and modules that you used in previous versions of cPanel & WHM.

cPanel & WHM ship with binaries that we compile against Perl version 5.36. This directly affects any custom Perl code that you execute from cPanel binaries. We **strongly** recommend that you test your plugins and hook code against Perl 5.36 to ensure that they work correctly.

Before you recompile all of your modules, check whether cPanel & WHM already includes your modules. With the addition of several modules to the list of modules that cPanel ships, we expect that cPanel & WHM ships with the majority of the modules that developers built with this tool.

* For a list of modules that cPanel currently ships, read our [Third-Party Software](https://docs.cpanel.net/knowledge-base/third-party/third-party-software/) documentation for the appropriate cPanel & WHM version.
* **cPanel wants to ensure that we ship the modules that developers need.** If you discover that cPanel & WHM does not ship with a CPAN module that you need, reach out to us in [Discord](http://go.cpanel.net/discord).


Note:
While it is possible to install custom modules to the `/opt/cpanel/perl5/514`/site_lib library with the `/usr/local/cpanel/3rdparty/perl/514/bin/cpanm` command, this will cause further problems when cPanel switches to newer versions of Perl in the future..