http://www.perlmonks.org?node_id=1010462


in reply to Access value of a variable after exit 0 in fork

The simplest would be to return a small numeric value via the exit code of the sub-process, read that in the parent process, and translate that in you main code to set $trigger to "ON".

The problem you currently have is that $trigger in the child process is in a different memory space, and modifying that in the child has no effect on the parent's instance of $trigger.

             "By three methods we may learn wisdom: First, by reflection, which is noblest; Second, by imitation, which is easiest; and third by experience, which is the bitterest."           -Confucius

  • Comment on Re: Access value of a variable after exit 0 in fork

Replies are listed 'Best First'.
Re^2: Access value of a variable after exit 0 in fork
by Anonymous Monk on Dec 27, 2012 at 08:53 UTC
    Can you please elaborate via some code? Sorry to give you trouble,but just want to understand thoroughly.
[reply]
      See perlipc and waitpid 
      if( my $pid = fork() ){
    print "parent ($$) is waiting on child $pid\n";
    my $kid ;
    do {
        $kid = waitpid(-1, WNOHANG);
    } while $kid > 0;
    my $exit = $? >> 8;
    die qq{Kid ($kid) exited with $? / $exit \n};
} else {
    print "I am the kid $$\n";
    sleep 1;
#~     exit 666; ## too big
    exit 12;
}
__END__
parent (1724) is waiting on child -880
I am the kid -880
Kid (-880) exited with 3072 / 12

      [download]

      There are abstractions to help you manage this like Parallel::ForkManager, Proc::Fork, forks, threads ....

[reply]
[d/l]

In Section Seekers of Perl Wisdom