#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1146191

use strict;
use warnings;

my $sequence = 'AATGGTTTCTCCCATCTCTCCATCGGCATAAAAATACAGAATGATCTAACGAA';

while( $sequence =~ /ATG/g )
  {
  my $rest = $';
  print 'ATG' . $` . $1 while $rest =~ /(TAG|TAA|TGA)/g;
  }