my $sub = 'CGAGCGTTGACGCNNAGCTAGT';
   my @bases = split //, $sub;

   my $count = 100;
   my $len = length $sub;

   @promoters_regex = (
      qr'[NT][GCATN][NG][NC][NG][NT][NG]',
      qr'[NG][NT][NG][NC][NG][GCATN][NT]',
      qr'[NA][GCATN][NC][NG][NC][NA][NC]',
      qr'[NC][NA][NC][NG][NC][GCATN][NA]',
   );

   my $permutations_total = 0;
   while ($count--)
   {
      my $ilen = $len;
      my $string;
      $string .= $bases[rand @bases] while $ilen--;

      foreach my $regex (@promoters_regex)
      {
         $permutations_totals += scalar($string =~ m/$regex/g);
      }
   }