#!/usr/bin/perl -w

use Getopt::Std;

sub stage1 {
  my $out;
  open $out,"|$0 -m2" or die "Can't fork.\n";
   
  while (<STDIN>) {
    chomp;   
    printf $out "S1>%s\n",$_;
  }

  close $out;
}
 
sub stage2 {
  my $out;  
  open $out,"|$0 -m3" or die "Can't fork.\n";
   
  while (<STDIN>) {
    chomp;      
    printf $out "S2>%s\n",$_;
  }

  close $out;
}

sub stage3 {
  my $out;
  open $out,"|$0 -m4" or die "Can't fork.\n";
   
  while (<STDIN>) {
    chomp;   
    printf $out "S3>%s\n",$_;
  }

  close $out;
}

sub stage4 {
  while (<STDIN>) {
    chomp;
    printf "S4>%s\n",$_;
  }
}

my %mode = (
  1 => \&stage1,
  2 => \&stage2,
  3 => \&stage3,
  4 => \&stage4,
  );

getopt("m:");
if (defined($opt_m)) {
  if (exists($mode{$opt_m})) {
    $mode{$opt_m}();
  } else {
    die "Mode '$opt_m' undefined.\n";
  }
} else {
  die "usage: $0 -m <mode>\n";
}