That's very confusing what you write.
If fork fails, undef is returned.
If fork succeeds, different values are returned
in the parent and the child. In the child, fork
returns 0, while in the parent, the process ID of
child is returned. This is the only convenient time for the
parent to get the process ID of the child. A parent can get
the process ID of the child when it's reaping the child with
some form of wait call, but then the child has
already finished. Otherwise, the parents rests nothing else
than walking the process list.
Abigail
