Found in /usr/lib/perl5/5.8.5/pod/perlfaq3.pod
       How do I find which modules are installed on my system?

       You can use the ExtUtils::Installed module to show all installed distributions,
       although it can take awhile to do its magic.  The standard library which comes with
       Perl just shows up as "Perl" (although you can get those with Module::CoreList).

               use ExtUtils::Installed;

               my $inst    = ExtUtils::Installed->new();
               my @modules = $inst->modules();

       If you want a list of all of the Perl module filenames, you can use File::Find::Rule.

               use File::Find::Rule;

               my @files = File::Find::Rule->file()->name( ’*.pm’ )->in( @INC );

       If you do not have that module, you can do the same thing with File::Find which is
       part of the standard library.

           use File::Find;
           my @files;

           find sub { push @files, $File::Find::name if -f _ && /\.pm$/ },
                @INC;

               print join "\n", @files;

       If you simply need to quickly check to see if a module is available, you can check for
       its documentation.  If you can read the documentation the module is most likely
       installed.  If you cannot read the documentation, the module might not have any (in
       rare cases).

               prompt% perldoc Module::Name

       You can also try to include the module in a one-liner to see if perl finds it.

               perl -MModule::Name -e1