You could kill INT, $pid; which is like hitting Ctrl-C. If the child is already gone, the signal will not be delivered to an unrelated process with the same pid. That shouldn't be a problem, anyway, if you are handling SIGCHLD.

Update: Re diotalevi's question, kill fails with EPERM if the real or effective uid of the sender is not root or the same as that of the $pid addressed. See 'man 2 kill'. It is true that one of the user's own processes could reacquire the child pid. That is why the SIGCHLD handler should arrange to note the death of $pid, so the issue of misdelivery never comes up.

After Compline,
Zaxo

Color me confused. So of the two parts, delivery and execution let me know where I'm off base. Does the INT not get sent to the non-child PID or is the INT somehow not honored by the non-child of the same pid? And how is this different from using kill(1) from the command line where it doesn't matter whether the process is a child or not. I did a quick read of kill from perlfunc and Signals from perlipc and I didn't see anything about INT not being sent to non-child processes. So what's the scoop here, how did you come up with that?

Update: then I wasn't wrong. Unstated was the assumption that normal user control functions so you can only kill your own processes. It's just unlikely that a given user ends up with another process at the same UID, not actually prohibited some how.

__SIG__
use B;
printf "You are here %08x\n", unpack "L!", unpack "P4", pack
  "L!", B::svref_2object(sub{})->OUTSIDE;
[download]

That sounds about like what I'm looking for. Thanks.

SpaceAce
s>>sp>;s>..|>\u$&ace>g;print;

To check whether your $PID is still the correct process, have a look at Proc::ProcessTable to browse throught the process table. This will give you a way to check whether process $PID is still the correct one:

use strict;
use Proc::ProcessTable;
my $table=Proc::ProcessTable->new;
my @procs=$table->table;
foreach $p ($table->table) {

  if ($p->pid == $saved_pid) {
    send_signal() if ($p->cmdline eq "expected command line");
  }
}
#Warning: code is utterly untested and not the most efficient either.
[download]

CU
Robartes-

1) I may not have made it clear that the control panel is not a constant process. It is web-based and every function you execute through the control panel is going to be a new process which will die and return the user to the control panel HTML page after it is done doing what it does. So, unless I am mistaken, the process created when a user hits the "Halt script" button would not be the parent of the child process, anyway.

2) I misunderstood the first answer given. It's a useful place for me to start doing some reading but it won't solve the problem I am currently dealing with.

I think checking the process group ID is the way for me to go. I don't want to anything to break the program for ActivePerl (I develop using Perl 5.6.1 on Linux), but I can always throw in an eval block to avoid any real problems.

Thanks again for all the help, Monks.

SpaceAce
s>>sp>;s>..|>\u$&ace>g;print;