What's being suggested is that you maintain a private build of Perl and all your Perl modules. Your applications' shebang lines would point at a different pathname (#!/usr/local/bin/perl, for example) and the perl on /usr/local/bin would be the perl you compiled and installed yourself. That perl would look for Perl modules on a completely different set of paths where it would find your privately maintained modules. The CPAN
is Perl's code repository. When you update or install new modules using the cpan command or perl -MCPAN -e shell
you're accessing this repository.