#!/usr/bin/perl -w

use strict;

my @array = ([ "a", "b", "c", ],
[ "1", "2", "3", "4", ],
[ "x", "y", ],
[ "U", "V", "W", "X", "Y", "Z",],);
my (@current, @result); # In @current we store the array index to construct the string

my $comb = 1;
map($comb *= @{$_}, @array); # Get total permutations

for (my $num = 1; $num <= $comb; $num++)
  {
  my $string = '';

  for (my $k = 0; $k <= $#array; $k++)
    {
    $current[$k] = 0 if !$current[$k];
    $string .= ${$array[$k]}[$current[$k]];
    }

  if ($current[$#array] < $#{$array[$#array]})
    {
    $current[$#array]++;
    }
  else #If we reach max index we increment previous not maxed one
    {
    $current[$#array] = 0;
    for (my $i = $#array-1; $i > -1; $i--)
      {
      # We exit the loop when we increment a not maxed index
      $current[$i] < $#{$array[$i]} ? do {$current[$i]++; last} : do {$current[$i] = 0};
      }
    }

  push(@result, $string);
  }

print join(",", @result) . "\n";