How do I check whether a Perl module is installed?

Question

I'm writing a small Perl script that depends on some modules that might be available, so during the installation I would have to check if everythings there. I could just write use some::module and see if an error comes up, but a short message like "You need to install some::module" would be more helpful for endusers.

I also could just search every directory in @INC, but as it's Perl, there has to be an easier way.

Answer 1

perl -MSome::Module -e ';'

Whoops, misread the question. I thought you wanted to know in a one-off instance, not discovering it in a recoverable manner. I always use something like this:

sub try_load {
  my $mod = shift;

  eval("use $mod");

  if ($@) {
    #print "\$@ = $@\n";
    return(0);
  } else {
    return(1);
  }
}

Which you use like this:

$module = Some::Module;
if (try_load($module)) {
  print "loaded\n";
} else {
  print "not loaded\n";
}

Answer 2

Check out the answers to this earlier question: How can I check if I have a Perl module before using it?

Answer 3

How about:

die "Some::Module missing!" unless(eval{require Some::Module});

Answer 4

I use something like this:

BEGIN { 
    my $module_name    = shift; # @ARGV
    our $module_exp = $module_name;
    eval "use $module_name;";
}

$module_exp =~ s{::}{/}g;
foreach my $key ( grep { m/^$module_exp\./ } keys %INC ) { 
    print "$key => $INC{$key}\n";
}

But I use this more in the form of a korn shell function:

function wherperl
{
     perl -M$1 <<EX_DOC
     my \$module = '$1';
     \$module =~ s/::/\\//g;

     for ( keys %INC ) {
         next unless m/^\$module\./;
         print \$_ . ' => ' . \$INC{\$_} . "\n";
     }
EX_DOC
}

Answer 5

How are you installing your script? If you are using a standard Makefile.PL or Build.PL, listing dependencies is trivial.

Answer 6

I have a little script that lists all the Perl modules on my system;

#!/usr/bin/perl

use ExtUtils::Installed;
my $instmod = ExtUtils::Installed->new();
foreach my $module ($instmod->modules()) {
    my $version = $instmod->version($module) || "???";
    print "$module -- $version\n";
}

Inside that foreach loop you might want to do some thing like;

my $match;
if ($module =~ /$match/) {
  print "Found $match: $module\n";
}

Answer 7

I like to use the cpan utility:

% cpan -D YAML
YAML
-------------------------------------------------------------------------
 YAML Ain't Markup Language (tm)
 A/AD/ADAMK/YAML-0.70.tar.gz
 /usr/local/perls/perl-5.10.0/lib/site_perl/5.10.0/YAML.pm
 Installed: 0.68
 CPAN:      0.70  Not up to date
 Ingy dot Net (INGY)
 [email protected]

This can be a little slow since it has to connect to a CPAN mirror to fetch some of the data, but I also have a local CPAN mirror. :)