«

According to the documentation of the open function the return value
should be

the pid of the child within the parent process, and 0 within the
child process. (Use "defined($pid)" to determine whether the
open was successful.)

As opposed to this, at least for perl 5.10.1, the open call will die
('croak', actually) with a message "Can't fork" when the fork failed
because of any error except EAGAIN.