my $PID = fork();
if ($PID) {
    # in the parent process
}
else {
    # in the child process
}

##</code><code>##

my $PID = fork();
if ($PID) {
    # in the parent process
}
else {
    # in either the child process or the parent
    # process, depending on whether the fork()
    # succeeded or failed.
}