XS for implementing these code: @data = unpack "C*", $script;

How much do you know about C?

Because the "equivalent of the above code in C makes no sense. A C string is already an array of bytes.

You don't need to pack or unpack a string(array of unsigned char), just access the elements.

If you do not understand enough C to understand that, you should think twice about using XS; cos it'll bite you in the arse. Hard.