#!/usr/bin/perl -w
use strict;

my $str = 'NNNNNATCGNNNNATCG';
my @substr  = qw(ATCG ATCG);
foreach (@substr)
{
   my $id = index($str,$_);
   print "$id\n"; 
}

##</code><code>##

5
5

##</code><code>##

5
13