You can skip the hex step with:

perl -e 'print unpack "s", pack "H*", "ffaa"'
[download]

If that's wrong on your system, it's an endian problem. {grin} So you can also try:

print unpack "s", pack "h*", scalar reverse "ffaa";
[download]

which does print -86 on my machine.

-- Randal L. Schwartz, Perl hacker