Make Perl Script to Compute Two's Complement on An 8-Bit Integer

I have written a Perl script that takes an input hexadecimal value and then retus the binary equivalent. I need to sign that 8-bit integer and view the signed integer's value. This particular scenario does not seem to be covered in the Perl documentation that I have seen. The script is pasted below:

    #! perl
    use waings;
    print "Enter hexidecimal number:";
    chomp ($hexNum = <STDIN>);
    print $hexNum . "n";
    print  join "n", map { unpack ('B*', pack ('H*',$_)) } split ':', 
    $hexNum;