Anonymous Monk,
There are plenty of modules on CPAN that will do this for you. There are also many examples of home grown code here you could have found using Super Search.

Are you sure you want combinations? There is a difference between combinations and permutations and you also need to consider replacement and duplicates. I think the following code, adapted from How To: Make An Iterator does what you want.

#!/usr/bin/perl
use strict;
use warnings;

# Change this as desired
my $size = 2;

my $next_perm = fix_size_perm($size, 'a'..'z', 0..9);
while ( my $perm = $next_perm->() ) {
    print "$perm\n";
}
sub fix_size_perm {
    my ($size, @list) = @_;
    my @curr = (0) x ($size - 1);
    push @curr, -1;
    return sub {
        if ( (join '', map { $list[ $_ ] } @curr) eq $list[ -1 ] x @cu
+rr ) {
            @curr = (0) x (@curr + 1);
        }
        else {
            my $pos = @curr;
            while ( --$pos > -1 ) {
                ++$curr[ $pos ], last if $curr[ $pos ] < $#list;
                $curr[ $pos ] = 0;
            }
        }
        return undef if @curr > $size;
        return join '', map { $list[ $_ ] } @curr;
    };
}
[download]

Update: Changed code example to hopefully better fit the problem.