sigchild and $?

Chapter_01 has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to catch the exit code of a shell script executed by my script. I used a friends code to 'daemonize' and then mask for signals with the 'POSIX' module.

The problem that I now have is once the following piece of code is run '$?' is always '-1' regardless of the exit from the last command run in (``)'s.

I have read that once a new sigchld is installed the $? cannot be trusted.

My question, is there any way to retain the '$?' or like behavior after messing with sigchld?

# START_SUB
sub setSigDisposition() {
  my ($sighandler,$snum);

  #
  # The set of signals to mask
  #
  my $sigset = POSIX::SigSet->new;
  $sigset->fillset();

  #
  # Don't mask these signals because wouldn't want to continue
  # if one these sent, even in critical section(s).
  #
  $sigset->delset( &POSIX::SIGILL );
  $sigset->delset( &POSIX::SIGSEGV );
  $sigset->delset( &POSIX::SIGFPE );
  $sigset->delset( &POSIX::SIGINT );

  foreach $snum( split(' ', $Config{sig_num}) ){
    $SIG{CHLD} = 'IGNORE';
    if( $snum == &POSIX::SIGILL || $snum == &POSIX::SIGSEGV || $snum =
+= &POSIX::SIGFPE || $snum == &POSIX::SIGINT ){
      $sighandler = "main::death";
    }
#    elsif( $snum == &POSIX::SIGTERM ){
#      $sighandler = "main::shutdown";
#    }
    else{
      $sighandler = "main::reaper";
    }

    # Set signal disposition ...
    POSIX::sigaction(
      $snum,
      POSIX::SigAction->new( $sighandler,
      POSIX::SigSet->new,
      &POSIX::SA_NOCLDSTOP ),
      POSIX::SigAction->new( $sighandler,
      POSIX::SigSet->new,
      &POSIX::SA_NOCLDSTOP )
    );
  }
  return $sigset;
}
# END_SUB
[download]

Thanks! -Bryan

Comment on sigchild and $? Download Code

Replies are listed 'Best First'.
Re: sigchild and $? by bluto (Curate) on Sep 30, 2003 at 22:29 UTC
Is there a reason you don't use something like waitpid()? FWIW, I've had -1 returned for $? in the past when I've set up SIGCHLD and then used perl's builtin fork/exec stuff (i.e. backticks, system(), qx()). I'm assuming perl (or the C library) sets up it's own waitpid() and/or sighandler for these expecting to reap the process and then I come along and screw things up with my SIGCHLD handler. Maybe someone with more wisdom can figure out how to do this right, but I tend to avoid setting up SIGCHLD and generally find that I don't need to. bluto	[reply]
Re: Re: sigchild and $? by Chapter_01 (Initiate) on Oct 01, 2003 at 13:03 UTC
I would love to say I had a reason for not using waitpid(), but that might be a stretch. I will play around with that a bit. I did find a work around - if interested: @ScriptMSG=`/run/some/script;/usr/echo "\$?"`; chomp(@ScriptMSG); $ExitCode=$ScriptMsg[$#ScriptMsg]; [download] -Bryan	[reply] [d/l]
Re: Re: Re: sigchild and $? by bluto (Curate) on Oct 01, 2003 at 15:58 UTC
I wasn't thinking straight -- forget my comment about waitpid() which you would need if you did your own fork/exec. You don't need it with backticks. Basically backticks sets $? so you can check it directly (by using this code ripped from 'perldoc -f system'... `$exit_value = $? >> 8; $signal_num = $? & 127; $dumped_core = $? & 128;` [download] bluto	[reply] [d/l]