I'd like to use the "pack" function to produce what hoepfully will appear as "00 00 00 00 00 09 fe 00" when viewed in emacs with the "hexl-mode" turned on.

That's a 64-bit int, so 
pack('q>', $_);  # Signed
pack('Q>', $_);  # Unsigned

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">" requires 5.10 (IIRC). "q" and "Q" require a 64-bit support. If you don't have a 64-bit support and your numbers aren't "very" large (<232), you could fake it using 

pack('NN', $_<0 ? -1 : 0, $_);  # Signed
pack('NN', 0, $_);              # Unsigned

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In using "pack" I need to figure out how to fill with spaces ("\x20") before the actual hex representation of the 654848. Any suggestions?

You were talking about converting a number to a native int, now you're talking about its hex representation. It's not clear what you're asking here. Assuming this is a completely separate question, 

sprintf('%8X', $_);   # Padded with spaces
sprintf('%08X', $_);  # Padded with zeros

[download]

Update: Added answer to second question.

In reply to Re: zero fill with pack by ikegami
in thread zero fill with pack by Spooky

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