#!/usr/bin/env perl 
use strict;
use warnings;

my $in = "ATATATTATATATATTATATTCGCGCGCGCGGCGCGCGCGGCGCGCGCGTTTTTTTTTTTTTTAGGAGAGAGAGGGAGGAGGAGAGGGGAGT";
my $out = '<pre>' . join ("\n", $in =~ /[ATCG]{1,50}/g) . "</pre>\n";
print $out;