[~]$ cat `which pmwhich`
#!/usr/bin/perl
use warnings;
use strict;

die "pmwhich module-name\n" unless @ARGV == 1;

my $module = $ARGV[0];
$module =~ s!::!/!g;

for my $dir (@INC) {
    my $fqn = "$dir/$module.pm";
    if (-e $fqn) {
        print $fqn, "\n";
        last;
    }
}

[~]$ pmwhich bigint
/usr/lib/perl5/5.8.5/bigint.pm
[~]$