The Cookbook uses the following example (listed on page 4)

# get a 5-byte string, skip 3, grab 2 8-byte strings, then the rest
($leading, $s1, $s2, $trailing) = unpack("A5 x3 A8 A8 A*",$data);
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x3 meaning to "ignore" 3 bytes (jump forwards), while Xm means to jump m bytes back.
A5 meaning to "get" 5 Ascii (space padded) bytes.
Another example would be to pack/unpack to/from binary or hexadecimal.

$string = "My uncle John is Jamaica";
$binary=unpack("B*",$string);
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and

$string=pack("B*",$binary);

Similar for Hexadecimal...

$string = "My uncle John is Jamaica";
$hexadecimal=unpack("H*",$string);
$string=pack("H*",$hexadecimal);
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Anyway, those were just the simple examples =)

Greetz
Beatnik
... Quidquid perl dictum sit, altum viditur.