#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my @result = ( '' );

my @plan = (
  [ qw/ CAT CAC / ],
  [ qw/ TGG / ],
  [ qw/ GTT GTC GTA GTG / ],
  [ qw/ CCT CCC CCA CCG / ],
  );

for my $step ( @plan )
  {
  my @new_result;
  for my $suffix ( @$step )
    {
    push @new_result, map { "$_$suffix" } @result;
    }
  @result = @new_result;
  }

print Dumper(\@result);