#!/usr/bin/perl
use warnings;
use strict;

for my $step (1..4) {
   sleep 3;
   print "Step $step\n";
}

##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;

$|++;
open PIPE1, "./blackbox.pl |";
while ( <PIPE1> ) {
   # ...Filter and munge $_
   print $_;
}
close PIPE1;