instmodsh only shows your locally installed modules - that is, the things you installed using CPAN. It will not list core modules or things that automatically come with your Perl distribution (for example, the debconf modules that are installed on all Debian systems).

To check if a particular module is installed, you can use the perldoc command:

• perldoc -l Foo::Bar prints out the full path to the module
• perldoc -m Foo::Bar displays the contents of the module file

If you want to see all the modules available given your current search path, try the following short script. This script works on both Win and *nix:

use strict;
use warnings;
use File::Find;

my @aModules;
foreach my $sDir (@INC) {
  my $crFind = sub {
    my $sModule = substr($File::Find::name, length($sDir)+1);
    push(@aModules, $sModule)
      if (($sModule =~ s/\.pm$//) || ($sModule =~ /\.pl$/));
  };
  find($crFind, ("$sDir/")) if -d $sDir;
};
print '' . join("\n", sort @aModules) . "\n";
[download]

Note: the main difference between oko1's solution and mine is that oko1 provides support for filtering your module list with regexes but does not sort modules or list .pl files. The solution above does not support regex selection but does sort modules and list .pl files.

Best, beth

Update: fixed cut&paste error in script.

Update: eliminated warnings for missing @INC dirs; insured directory name is terminated with "/" so that File::Find doesn't think directory names with dots (e.g. /usr/share/perl/5.8) are files and skip them -silly File::Find) - with thanks to oko1 whose code sample below alerted me to these problems. Also added note comparing oko1 solution below and this solution.