#!/usr/bin/perl -w

use strict;

my @tests = (
  'ATCG',
  'ATCGGTATATATRGTCGAYGCRGTCAGA',
  'ATCGGTATATATRGTCGAYGCNGTCAGA',
);

foreach (@tests) {
  if(/^[ATCG]*([RYMKSWHBVDN])?(?:[ATCG]|\1)*([RYMKSWHBVDN])?(?:[ATCG]|\1|\2)*$/i){
    print "$_ matches\n";
  } else {
    print "$_ does not match\n";
  }
}