my %uniq=();
my $string = 'ACRMGAHKMAHGTXX';

      substr($string, $_, 10 ) =~ m[([AGTC].{0,8}[AGTC])]
      and ++$uniq{ $1 }
      for 0 .. length( $string )-1;

for my $key (keys %uniq){
    print $key, "\n";
}