How do I check whether a Perl module is installed? [duplicate] - perl

Question

This question already has answers here:
How can I require an optional Perl module if installed?
(8 answers)
Closed 9 years ago.
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

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

Answer 3

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 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

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)
ingy#cpan.org
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. :)