You should use pack and unpack as was pointed out already, but the error in your script is here: 
    printf("%X", ord($buffer))

[download]
One Byte can be 0 to FF in hex. If you have a stream of hex characters, how can you know you have 1A (26 in decimal) or two numbers, 1 and 10?

say 

    printf("%02X", ord($buffer))

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to make shure each byte is represented by 2 chars (e.g. 0A for decimal 10 instead of just A). Converting back you have to read 2 Bytes each time.

--shmem 

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

In reply to Re: Recreating a binary file from hex representation by shmem
in thread Recreating a binary file from hex representation by choedebeck

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