#!/usr/local/bin/perl -w

use strict;
use Data::Dumper;

{
   my %hash = ();

   while (<DATA>)
   {
      my $s;

      $s .= "{'$_'}" foreach (/(...)/g);

      eval ('$hash ' . $s . '++');

      die $@ if $@;
   }

   print Dumper ([\%hash]);
}

__DATA__
aaabbbcccddd
aab
aacbbb
aaabbacca
aaabbaccb
ababbbddd