Background: perl abstracts the system call killpg() and warps it into kill() with negative signal numbers. So, if you call kill(-15, $pid), perl translates it to killpg(15, $pid) on systems that support killpg().

Problem is that in order to run killpg(0, $pid), I'd have to call kill(-0, $pid) which is the same as kill(0, $pid) and won't trigger the special killpg(0, $pid) behavior.

So, there's no way to check if a process is up but hasn't called POSIX::setsid() or POSIX::setpgid() yet, causing kill(15, $pid) to succeed but kill(-15, $pid) to fail.

Any way around that? I could roll my own killpg() XS module, but I'd rather have it portable across Unix flavors and, ideally, use something that already comes with perl.