I tested the method on this page and several of those linked from it and it gives me the correct size every time (as compared to the same data dumped to a file in binmode).

I am pretty certain that the problem is that you are using unpack incorrectly. If you would care to post an example of the how you are using it, and a (small) sample of data that you are using it on, then I am certain that we could sort it the problem out.

Your reply to pfaut below indicates that you are either trying to use the '/' template character, which will never give you the answers that you require, or you are mixing up the information from different parts of the pack/[and unpack documentation--which would be no surprise as it is probably some of least understandable of the perldocs.

Pack/Unpack Tutorial (aka How the System Stores Data) might help you figure out how to use pack/unpack.

---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';
[download]

I played around with unpack, and it appears as if the following line from the pack() perldoc (5.6 and 5.8)page is true:

The length-item is not returned explicitly from unpack.

Any other ideas? I know I can write this out to a file, but it seems crazy to me to have to do that just to get a proper byte count.

Jeff