Here is *maybe* another way to get what you want - not really sure about this, but here it is. How about having blackbox.pl write to a fifo (named pipe), and then having the script above read from the fifo? All you need to do is:

  1. create the fifo using 'mkfifo', and make sure blackbox.pl
     has write permissions to it.
  2. change blackbox.pl to write to the fifo file, instead
     of writing to STDOUT.
  3. change your script above to read from the fifo file
     instead of from PIPE1, like this

        my $fifo_file = "/path/to/my_fifo";
        open FIFO, "<$fifo_file" or die "Can't read $fifo_file: $!";
        while (<FIFO>) {
             # ...Filter and munge $_
             print $_;
        }
[download]

You'll have to play with this a little to get it to work the way you want, but basically written this way, this script(reading from FIFO) will block on the while (<FIFO>) until something is written to the fifo file.

Just for some more reference, the Perl Cookbook pages 576-580 has a recipe for working with a fifo. Also, Programming Perl 3rd Edition p.433 describes Named Pipes.

HTH.