To clarify a little bit (I hope), Perl's strings are a string of
bytes, which may or may not be a string of printable characters. When Perl is asked to print a string, it just outputs all of the bytes in the string, one after the other. In this case, the bytes are
0x41 0x42 0x43 0x44, which happen to be the ASCII character codes for
ABCD.
Update: As pg mentions below, this terminology might be wrong in the face of Unicode. If, for the sake of this example, you temporarily pretend Unicode doesn't exist, hopefully this comment will still shed some additional light. :-)