Slightly off-topic: Your code block here:

$t = unpack('C', $foo);
if ($t == 0) { $v = unpack('C', substr($foo, 1)) }
elsif ($t == 1) { $v = unpack('S', substr($foo, 1)) }
elsif ($t == 2) { $v = unpack('L', substr($foo, 1)) }
elsif ($t == 3) { $v = unpack('Z*', substr($foo, 1)) }
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could also be this:

my @unpack_types = qw( C S L Z* );
$t = unpack('C', $foo);
$v = unpack($unpack_types[$t],  substr($foo, 1));  #Is $t always a num
+ber?
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You would probably do the same thing later on, when you take another look at this code :) I know it's not much savings for only four types, but I don't know what you're working on -- you could have 12! :)