That doesn't differentiate between which modules were installed as part of the Perl core, and which were installed after the fact. The OP is interested in knowing which modules were bundled with Perl. We already got a pretty good answer; perlmodlib
has a mostly
up-to-date listing of Perl's core modules. My counter-question was how to determine which modules I've installed that didn't
ship with Perl as a core module.
I guess, to your point, I could use File::Find to resurse Perl's @INC paths, keeping track of the names of all modules found, and then compare that list to the one provided in perlmodlib.