#!/usr/bin/perl -w
use strict;
use Algorithm::Loops 'NestedLoops';

my $length= 4;
my @chars = ('a' .. 'd');

my $get_combo = NestedLoops([ (\@chars) x $length ]);

my @combo;
while ( @combo = $get_combo->() ) {
    print "@combo\n";
}