If you need the output from both stdout and stderr via a single stream:

#main

my $kid = open my $fh, "theExternalProcess 2>&1 |" or die $!;
while( <$fh> ) {
    ## Read the output from theExternalProcess
}
## You'll end up here when the kid goes away
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If you need to keep stdout and stderr separate, then see IPC::Open3 or IPC::Run.

Thanks for that reply. I needed to keep them separate but managed in the end to find both a solution and the reason for me to have the trouble in the first place. Seems like I forgot to flush the stream which made it seem the processes did not work in parallel;

<P> select((select(STDOUT), $|=1)[0]);
<P> And the whole script that made it all work:
<br>
<br>$pid = open3(*CMD_IN, *CMD_OUT, *CMD_ERR, $path, @arguments);
<br>  close(CMD_IN);
<br>  
<br>  $selector = IO::Select->new();
<br>  $selector->add(*CMD_ERR, *CMD_OUT);
<br>
<br>  while(@ready = $selector->can_read) {
<br>    foreach my $fh (@ready) {
<br>      if(fileno($fh) == fileno(CMD_ERR)) {
<br>        my $line = scalar <CMD_ERR>;
<br>        if(defined $line) {
<br>          parseErrorStream($line);
<br>        }
<br>      }
<br>      else {
<br>        my $line2 = scalar <CMD_OUT>;
<br>        if(defined $line2 and $print eq 1) {
<br>          parseStandardStream($line2);
<br>        }
<br>      }
<br>      $selector->remove($fh) if eof($fh);
<br>    }
<br>  }
<br>  close(CMD_OUT);
<br>  close(CMD_ERR);
[download]