...
my $pid = fork(); # spawn child

if ( $pid ) { # parent
  while ( wait != -1 ) {
    while (<>) {
      print "Got $_ on STDIN\n";
    }
  }
} else {  # child
  while ( 1 ) {
    print $header;
    print `ps guw | sort -n -r -k $sort_option | head -$num_lines`;
    print "\nSort: $sort_option : Lines: $num_lines : Sleep: $sleep_time\n";
    sleep $sleep_time;
    print `clear`;
  }
}