Sorry to post this again, but is seems that once the thread is a day or two old, no one looks at it and I still don't have an answer... I am submitting multiple commands in parallel using Run_parallel using a Tk GUI. The commands that I am running can take up to 5 minutes to complete (or time out). I am submitting these in the background on a UNIX system (&). With the current subroutine, If the commands are submitted one at a time, STDERR comes back fine. However, if I submit several at once, I only get STDERR back for the LAST command to complete. How can I get STDERR back for ALL commands? I cannot use any CPAN modules. 
sub run_parallel {
  my $job_count = shift;
  unless (0 < $job_count) {
    confess("run_parallel called without a positive parallel job count
+!");
  }
  my @to_start = @_;
  my %running;
  my %errors;
  my $is_running = 0;
  while (@to_start or %running) {
    if (@to_start and ($is_running < $job_count)) {
      # Launch a job
      my $job = shift @to_start;
      unless (ref($job)) {
        $job = [$job];
      }
      open (NULL, $null_file) or confess("Cannot read from $null_file:
+$!");
      my $proc_id = open3("<&NULL", \*CMD_OUT, \*CMD_ERR, @$job);
      $running{$proc_id} = $job;
      ++$is_running;
    }
    else {
      # collect a job
      my $proc_id = wait();
      if (! exists $running{$proc_id}) {
        confess("Reaped unknown process $proc_id!");
      }
      elsif ($?) {
        # Oops
        my $job = $running{$proc_id};
        my ($cmd, @args) = @$job;
        my $err = "Running '$cmd' gave return code '$?'";
        if (@args) {
          $err .= join "\n\t", "\nAdditional args:", @args;
        }
        $errors{$proc_id} = $err;
      }
      delete $running{$proc_id};
      --$is_running;
    }
  }
  return %errors;
 $mw_status_window->fileevent(\*CMD_OUT, 'readable', \&read_out);
 $mw_status_window->fileevent(\*CMD_ERR, 'readable', \&read_err);
}

sub read_out {
my $line = <CMD_OUT>;

unless ($line) {
   close(CMD_OUT);

  } else {
   print "green", "$line\n";
  }
}

sub read_err {
my $line = <CMD_ERR>;

 unless ($line) {
   close(CMD_ERR);
  } else {
   print "red", "$line\n";
  }
}

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In reply to Gathering STDERR from multiple commands.... by Capt_Howdey

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