How can I output my numbers with commas added?

This one will do it for you: 

    sub commify {
	local $_  = shift;
	1 while s/^(-?\d+)(\d{3})/$1,$2/;
	return $_;
    }


    $n = 23659019423.2331;
    print "GOT: ", commify($n), "\n";


    GOT: 23,659,019,423.2331

You can't just: 

    s/^(-?\d+)(\d{3})/$1,$2/g;

because you have to put the comma in and then recalculate your position.