When using the system Perl, you cannot upgrade modules via CPAN.

This is a reason for not using CPAN to upgrade modules within the system perl installation - not a reason for not using the system perl at all. Each (reasonable) OS provides its own packager, and each packager has means to install modules elsewhere, apart from the system's locations.
For some reason, there is:

and so on. Then PERL5LIB, lib.pm, FindBin.pm et al.

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

In reply to Re^2: RFC: (Do Not) Modify the System Perl by shmem
in thread RFC: (Do Not) Modify the System Perl by MidLifeXis

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