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.

Yes, you could do all sorts of things to this effect. You could take a list of modules which might be installed by default by your Perl distribution and compare it with what is installed. You've solved your own problem. <grins /> I was trying to provide suggestions to see whether or not it helped anyone.