Dot "." is the "match-all" character in a regex so your split won't return anything.

Actually split returns a lot of things, it's just that the way list assignment works there is nothing left to put in the array.    If you make a slight change you can see everything that split returns:

$ perl -le'my $ip="158.21.17.45"; my @values = split(".", $ip, -1); pr
+int $ip,"\t\t",$#values,"\n";'
158.21.17.45            12
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Not sure what you mean about list assignment; the difference is that a third parameter of -1 makes split keep trailing empty strings where by default it discards them. In your example, split returns 13 empty strings (one from before the first character of $ip, one for each position between characters, and one from after the last character.)
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