Close. But ord($_) returns 0 not because it contains a null byte, but because it is an empty string.

print ord("");
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prints: 0
(Where on earth would he be getting null bytes from?)

Indeed, the resulting array he's getting after doing

$ip = "21.23\n";
@t = split /./, $ip;
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is

("", "", "", "", "", "\n")

The explanation: every character in the input string, except the newline, is used as a split delimiter. Thus you get, as a result, the stuff between those characters, which is nothing every time, except at the last character.