How do I find what Perl modules are installed on my system?

Assuming you have perldoc installed, simply typing perldoc perllocal will give you a nicely-formatted detailed list of all the installed Perl modules.

For a simpler list that simply prints out the module names and their version numbers, there is another alternative. You must have the ExtUtils::Installed module installed in order to use it. Enter this code into a file and have Perl run it.
#!/usr/local/bin/perl
use ExtUtils::Installed;
my $instmod = ExtUtils::Installed->new();
foreach my $module ($instmod->modules()) {
my $version = $instmod->version($module) || "???";
@ print “$module — $version\n”;@
}

See this page from the CPAN FAQ for more details.