abaugher@bannor:~/work/perl/monks$ cat 938978.pl
#!/usr/bin/perl
use Modern::Perl;
use Benchmark qw(:all);;

my( $aa, $bb ) = ('','');

$aa .= chr(65 + rand(26)) for (1..50);
$bb .= chr(65 + rand(26)) for (1..50);
say $aa;
say $bb;

my @aa = split //, $aa;
my @bb = split //, $bb;

cmpthese(100000, {
    'grep' => \&usinggrep,
    'tr'   => \&usingtr,
    'sg'   => \&usingsg,
});

sub usinggrep {
    my $sum = 0;
    for my $l ('A'..'Z') {
        my $acount = grep /$l/, @aa;
        my $bcount = grep /$l/, @bb;
        $sum += abs($acount-$bcount);
    }
    return $sum;
}

sub usingtr {
    my $sum = 0;
    for my $l ('A'..'Z') {
        my $acount = eval "'$aa' =~ tr[$l][$l]";
        my $bcount = eval "'$bb' =~ tr[$l][$l]";
        $sum += abs($acount-$bcount);
    }
    return $sum;
}

sub usingsg {
    my $sum = 0;
    for my $l ('A'..'Z') {
        my $acount = $aa =~ s[$l][$l]g || 0;
        my $bcount = $bb =~ s[$l][$l]g || 0;
        $sum += abs($acount-$bcount);
    }
    return $sum;
}

abaugher@bannor:~/work/perl/monks$ perl 938978.pl
FHORAICOBMUCUMNYLRCUMVAMGXRRCADIZVTZTRENIEOBGNXSQT
JIPPTFERERTBOQOPNQSGWDTTOZOTHNXPEKJACSXEQBOAPIMSHI
       Rate   tr grep   sg
tr    924/s   -- -45% -88%
grep 1682/s  82%   -- -79%
sg   7849/s 749% 367%   --