# Assumes ASCII.
$string1 = "@@@@@";
$string2 = "ABCDE";
$xored = $string1 ^ $string2;
print($xored eq "\x01\x02\x03\x04\x05" ? "ok\n" : "not ok\n");

##</code><code>##

my $repeats     = (length($cipher_text) / length($pass)) + 1;
my $pass_stream = substr($pass x $repeats, 0, length($cipher_text));
my $plain_text  = $cipher_text ^ $pass_stream;

##</code><code>##

foreach my $c1 ('a'..'z') {
foreach my $c2 ('a'..'z') {
foreach my $c3 ('a'..'z') {
   my $pass = $c1 . $c2 . $c3;
   ...
}}}