Of course there is no guarantee that your modules are installed in /usr/ so you may want to find the directories you are searching using the following code if you are using b10m's solution

Of course there's no guarantee, that's why I wrote "most likely". "My solution" comes in handy when you know you installed the modules, but you somehow can't seem to use them (read: they're not in %INC). Otherwise, I would strongly suggest to use for example borisz' solution.

I understand. I was pointing out a way to double check where the modules were installed.

Note that you need read access to these directories, so if your box is properly locked down this may mean you need root access.

You would have quite a paranoid sysadmin, if you can't read the Perl modules' directories, but of course, it's possible :)

Not really. It is standard procedure on a lot of boxes to make a directory readable but not executable, so you can access any programs you know the path of, but you can't list the directories contents. This means that although % ls -l /usr/bin wouldn't tell you what programs were installed, /usr/bin/perl would still work because you could read and execute the program /usr/bin/perl although you couldn't figure out if someone had perl installed by % ls /usr/bin/perl. Install programs in non standard paths and users can't even guess the path.

Update: fixed my dyslexia. Thanks b10m!