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

I ran into an odd situation in a program I'm writing and wrote this simple test program to show it: when run, it repeats "It's alive!" indicating that kill is failing to kill the process the same program opened. Call me puzzled... 
#!/usr/bin/perl

use strict;

my $stuff_cmd = 'sleep 10';

my $cam_fh;
my $cam_pid = open($cam_fh, "$stuff_cmd|");

print "cmd running: $cam_pid\n";
sleep 1;

print "killing cmd: $cam_pid\n";
while ((my $count = kill -9, $cam_pid) != 1) {
    print "It's alive!!!!!\n";
    sleep 1;
}

print "cmd closed off\n";
close($cam_fh);

print "dead and buried!\n";

exit 0;

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Re: kill won't kill the process I opened
by keszler (Priest) on Sep 16, 2013 at 03:34 UTC
    Perl kill != *nix kill. According to kill:

    A negative signal name is the same as a negative signal number, killing process groups instead of processes. For example, kill '-KILL', $pgrp and kill -9, $pgrp will send SIGKILL to the entire process group specified. That means you usually want to use positive not negative signals.
    With kill 'KILL', $cam_pid I got: 
    $ ./pm1054213.pl
cmd running: 7808
killing cmd: 7808
cmd closed off
dead and buried!

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Re: kill won't kill the process I opened
by kcott (Archbishop) on Sep 16, 2013 at 03:43 UTC

    G'day useopenid,

    I suggest you start by reading the kill documentation.

    A negative signal is for process groups.

    To see whether a process is still running, check the truth of: 

    kill 0 => $pid

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    -- Ken

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Re: kill won't kill the process I opened
by useopenid (Initiate) on Sep 16, 2013 at 03:33 UTC
    Further info: I modified the "it's alive" to print out $! also and it's getting "No such process", but the process does exist and hasn't switched to any other user: 
    $ zt
cmd running: 18859
killing cmd: 18859
It's alive!!!!! (No such process)
It's alive!!!!! (No such process)
It's alive!!!!! (No such process)

$ ps aux
...
alan     18858  1.0  0.4   5660  1932 pts/2    S+   20:30   0:00 /usr/
+bin/perl ./zt
alan     18859  0.0  0.1   3184   492 pts/2    S+   20:30   0:00 sleep
+ 10

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Re: kill won't kill the process I opened
by Anonymous Monk on Sep 16, 2013 at 03:40 UTC
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