# break into individual characters
my @characters = split(//);

# or if you want ASCII values
my @characters = unpack("C*");

# of if you wish to use a loop
while (/(.)/g) { # . is never a newline
     # do something with $1
}

##</code><code>##

my %seen = ();
my $string = "J. J. Horner is so cool!";
foreach my $byte (split //, $string) {
    $seen{$byte}++;
}
print "unique chars are: ", sort(keys %seen), "\n";