To find all modules in all @INC directories:

findpm
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I bet searching here on monks would have given you a few examples of how monks do this. There is a plethora of scripts available by now as there are many ways to answer the question.

I also wrote a script myself, but with a few additions to make it easier to find module not (yet) installed, so that I don't have to dig on CPAN when I'm looking for a module that does XML/XPM/CSV/mysql/...

Note that my script works based on the list of modules available as seen by CPAN, so it will not find modules that were manually copied into the perl tree.

$ modlist -?
usage: modlist [ -a AUT ] [ -r ] [ -i ] [ -nc ] [ <pattern> ]
        -a | --author=AUTHOR_ID  Only modules from author
        -r | --registered        Only registered modules
        -i | --installed         Only installed modules
        -n | --new               Only new modules
        -c | --csv               Output module and version as CSV
        <pattern>                Only modules that match pattern
$ modlist -i xpm
Module name               Description                                 
+ Version
Bundle::Image::Info::XPM                                              
+     0.01
Image::Info::XPM                                                      
+     1.07
Image::Xpm                                                            
+     1.12
Tk::XPMs                                                              
+     1.11
$ modlist -r peek
Module name               Description                                 
+ Version
Apache::Peek              Devel::Peek for mod_perl
Data::Peek                A collection of low-level debug facilities  
+     0.31
Devel::Peek               Peek at internal representation of Perl data
+     1.04
                          Core since    5.006 1.00_01      in 5.010001
+     1.04
POE::API::Peek            Peek into the internals of a running POE env
$
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It also does colorizing (when available), shows if it is a CORE module (using Module::Corelist), since when and what version in core,

Yeah, I did the search as suggested, and found it lacking. All I want is a way to use Module::Corelist to list the modules that are installed with perl on my box. Pretty simple, I'd say, but nothing I've found here on this site, seems to just do that. I read the doc from CPAN on Module::Corelist, and came up empty there also. Is this really that tough of a request? Just a simple script that uses Module::Corelist to list the installed modules. That's it.

Revised comment: Thank you, I did finally find one. Not simple by any means, but I did find one.

You could try using the ExtUtils::Installed and Module::CoreList modules. Here is an example that finds all modules and displays the version numbers of each:

#!perl
use strict;
use warnings;
use feature qw(:5.12);

use ExtUtils::Installed;
use Module::CoreList;
use Module::Info;

my $inst  = ExtUtils::Installed->new();
my $count = 0;
my %modules;
foreach ( $inst->modules() ) {
    next if m/^[[:lower:]]/;    # skip pragmas
    next if $_ eq 'Perl';       # core modules aren't present in this 
+list,
                                # instead coming under the name Perl
    my $version = $inst->version($_);
    $version = $version->stringify if ref $version; # version may be r
+eturned as
                                                    # a version object
    $modules{$_} = { name => $_, version => $version };
    $count++;
}
foreach ( Module::CoreList->find_modules() ) {
    next if m/^[[:lower:]]/;    # skip pragmas
    my $module = Module::Info->new_from_module($_) or next;
    $modules{$_} = { name => $_, version => $module->version // q(???)
+ };
    $count++;
}
foreach ( sort keys %modules ) {
    say "$_ v$modules{$_}{version}";
}
say "\nModules: $count";
__END__
[download]

Update: Links fixed.

I have a script that finds and lists all the installed modules on a system

A slight variation on that theme for listing all the distributions that are installed

pminst - shows all installed modules
pminst -l - shows all installed modules with full path

To match a particular text string, I'll use 'sample':

pminst '(?i)sample'

unfortunately, pminst is part of pmtools, which isn't part of the core. And wouldn't work anyway where I work.

use  cpanp -b or  cpan -a or App::Module::Lister, How to clean-up an autobundle so it's really "auto-installable", pminst

pmodinfo ought to do the job as well

Have you tried it on debian?

It relies on .packlist files, and IIRC, debian (or some other distro) removes these files, thus instmodsh doesn't work

These tool could do it
which_pm / Module::Which
pm_which / Module::Util
pmlist / App::PMUtils
App::Module::Lister

These also help

App::pmuninstall/pm-uninstall

cpan-outdated/ App::cpanoutdated

cpanm/ App::cpanminus

Thanks for the info Anon: I haven't tried it on debian yet. What about lsmod ?- I think this can be used in debian.

Yup, that did exactly what I needed. Thanks

To see all the modules you've installed using something like cpanm, do: perldoc perllocal

To see a list of system packages on a Debian-based system (that is, ones installed via apt), do:

dpkg -l | grep 'lib.*\?-perl'

Also, corelist can show you all core modules installed for any version of Perl 5 you care to ask about, for example:

corelist -v 5.16.2