while(<FILE>){
(s!>.*(\n)!!);
my @words = (A, C, G, T); #letters to search
my @file = split (/\w/g, <FILE>); #split each letter into an array

        foreach $file (@file){
                foreach $words (@words){
                        if ($file eq $words){
                                $word_list{words}++;
                        }
                }
        }
@pairs = sort {$a->[1] <=> $b->[1]}
        map {[ $_ => $word_list{$_}]}
                keys %word_list;

        print "word $_ ->[0] = $_->[1]\n" for @pairs;