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

my $pro = "ABCDEFGH";
my @tetras;

push @tetras, [$1, $+[0] + 1] while $pro =~ /(?=(.{4}))/g;
print "$_->[0] -> Starting at pos $_->[1]\n" for @tetras;

##</code><code>##

ABCD -> Starting at pos 1
BCDE -> Starting at pos 2
CDEF -> Starting at pos 3
DEFG -> Starting at pos 4
EFGH -> Starting at pos 5