Also from perlrun

-f

Disable executing $Config{sitelib}/sitecustomize.pl at startup.

Perl can be built so that it by default will try to execute $Config{sitelib}/sitecustomize.pl at startup. This is a hook that allows the sysadmin to customize how perl behaves. It can for instance be used to add entries to the @INC array to make perl find modules in non-standard locations.

- Miller