my $wait = 0;
my $pid = system(1,"cmd...");

do {
    $wait = waitpid($pid,WNOHANG);
} while ($wait != -1);
$rc = $?;

print "Command completed with exit code $wait with return code $rc.\n"
+;
[download]

You call waitpid after you've reaped the process, causing causing an error ($? = -1;, error message in $!).

You gotta check $? after the successful call to waitpid.

use POSIX qw( WNOHANG );

my $pid = system(1,'perl -e"sleep(4); exit(5);"');

while (1) {
   my $wait = waitpid($pid, WNOHANG);
   die $! if $wait < 0;
   last if $wait > 0;
}

print "Command completed with exit code $?.\n";
[download]

I presume you actually do something else in the loop? If not, there's no reason to use WHOHANG.

my $pid = system(1,'perl -e"sleep(4); exit(5);"');

waitpid($pid, 0);
die $! if $? < 0;
print "Command completed with exit code $?.\n";
[download]

I may have answered my own question... I still can't figure out how to get it to work with waitpid but it does work properly when using just plain "wait". The reason I wasn't doing that before is that it is a blocking call so it prevents me from looping through checking each PID I kicked off previously. However, it seems that it blocks until any of the processes returns. The wait call itself returns the PID that just terminated and just after $? returns the status. So presumably I can collect all my PIDs as I kick them off then loop through on a blocking wait one by one waiting for each of those PIDs to terminate and collect the status as they do.

The following seems to do what I want:



my $pid1Complete = 0;
my $pid2Complete = 0;
my $pid3Complete = 0;
my $pid1 = system(1,"cmd...");
my $pid2 = system(1,"cmd...");
my $pid3 = system(1,"cmd...");

my $finishingPID = 0;
do {
    $finishingPID = wait();
    $rc = $?;
    if ($finishingPID == $pid1) 
    {
        $pid1Complete = 1;
        print "PID1 finished with return code $rc\n";
    }
    elsif ($finishingPID == $pid2)
    {
        $pid2Complete = 1;
        print "PID2 finished with return code $rc\n";
    }
    elsif ($finishingPID == $pid3)
    {
        $pid3Complete = 1;
        print "PID3 finished with return code $rc\n";
    }
} while (($pid1Complete == 0) || ($pid2Complete == 0) || ($pid3Complet
+e == 0));
[download]



If anybody has any suggestions for improvements or other ideas I'd be happy to hear them.

Thanks again.