@array = unpack("C*", $string);
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and then go through the array doing the xoring like this:

foreach $char (@array) {
    push (@xor_array, ($char ^ (shift @crypt_array)));
}
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That said, I really hope you are just doing this as a learning exercise because this is an incredibly insecure way to do encryption. Even if the xor string (your one time pad) is *truly* random, the algorithm calls for repeating it if you run out. As soon as you do that the cipher text can be cracked easily. Also, if your pad is not truly random, it doesn't matter whether you repeat it or not.

Hope this helps,
Mark