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

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Perl: How do I find which modules are installed on my system?
posted Apr 29, 2014 by Anuradha Tabyal

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1 Answer

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From the command line, you can use the cpan command's -l switch:

$ cpan -l

You can also use cpan 's -a switch to create an autobundle file that CPAN.pm understands and can use to re-install every module:

$ cpan -a

Inside a Perl program, 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->
    extras({follow => 1})->
    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(
        {
        wanted => sub {
            push @files, $File::Find::fullname
            if -f $File::Find::fullname && /\.pm$/
        },
        follow => 1,
        follow_skip => 2,
        },
        @INC
    );
    print join "\n", @files;

If you simply need to check quickly 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):

  $ 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

(If you don't receive a "Can't locate ... in @INC" error message, then Perl found the module name you asked for.)

answer Apr 30, 2014 by Simranjeet Singh
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#!/usr/bin/env perl

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$ perl -le 'system "df -h"'
$ perl -le 'system "df","-h"'

Both two styles work fine. What's the difference between them and which is better usage?

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