"Real Perl Hackers Use 'pack'" (tm)

If you are happy with it working on a range from 0-255:

$decimal = 123;
$hex = unpack( "H*", pack( "C", $decimal ) );
print "$hex\n";
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Use 'S' or 'L' (for short or long) instead of 'C' to get 16-bit or 32-bit decimal values working.

You can pack from and unpack to any format described in perlfunc/pack, so it might be described as 'all-purpose'.

Personally I always get this the wrong way round the first time but when it works it works nicely. Probably efficient too, but who knows.

If I'm really honest I'd go with 'sprintf', but hey. This is fun too.