#/usr/bin/perl
   
   use warnings;
   use IO::Socket::INET;
   use Scalar::Util;
   
   $port = '7777';
   if ( defined $ARGV[0] ) { $port = $ARGV[0] }
   $SIG{ 'TERM' } = $SIG{ 'INT' } = sub {
    
      print( "died() or caught TERM/INT\n" );
      exit();  
   };

   $SIG { 'PIPE' } = 'IGNORE';
   
   pipe( $reader, $writer );
   $writer->autoflush(1);
   
   if ( ! defined ( $pid = fork() ) ) {
	
      die( "Cannot fork!: $!" )

   }
   elsif ( $pid == 0 ) {
      
      # Child
      #
      $line = ''; # A line of data to be read
      
      # Connect to socket
      #
      $connected = 0;
      while ( 1 ) {
               	
         eval {

            undef $socket;
            $socket = IO::Socket::INET->new (
                                              PeerHost => '127.0.0.1',
                                              PeerPort =>  $port,
                                              Proto    => 'tcp'
                                             );
         
         };
         if ( $@ ) { print "$@\n" }

         if ( defined $socket ) {
         	
         	print( "Connected!\n" );
            $connected = 1;
         
         }
         else {

            print( "Could not connect!\n" );
            $connected = 0;
            die();
			
         }
         
         close $writer;
         while ( $connected ) {
            
            defined ( $line_2 = <$reader> ) or last;

            print( "CHILD: Received line $line_2\n" );
            eval {
         		
               if ( defined $socket->send( $line_2 ) ) {
         		 
                  print ( "CHILD: \$socket->send() successful: $line_2\n") ;
                  #shutdown( $socket, 1 );
                  $response = "";
                  $socket->recv($response, 1024);
                  print "CHILD: received response: $response\n";
               }
               else {
               	
               	print( "Not connected!\n" );
                  $connected = 0;

               }
               
            
            };
            if ( $@ ) { print( "CHILD: error when trying to send(): $@" ) }     
         }
         close $reader;
            
      }

   }
   else {
      	
      # Parent
      #
      close $reader;
      for ( $i=1; $i<=5; $i++ ) {
      		
         $line = "-- " . $i . " --";
         print( "PARENT: Going to transfer line $line\n" );

         eval {
            
            if ( print $writer "$line\n") {
               
               print ( "PARENT: Successfully pushed to child!\n" );
            }
         
         };
         if ( $@ ) { print( "$@\n" ) }
         
         sleep 1;
                                  
      }
      close $writer;
      print "PARENT: closed writer, waiting for child to exit\n";
      1 while wait > 0;

   }




##</code><code>##

use IO::Socket::INET;
 
my $port = '7777';
if ( defined $ARGV[0] ) { $port = $ARGV[0] }
# auto-flush on socket
$| = 1;

$SIG{ 'TERM' } = $SIG{ 'INT' } = sub { $socket->close(); };
$SIG{ 'PIPE' } = 'IGNORE';
my $client_socket;

# creating a listening socket
my $socket = new IO::Socket::INET (
    LocalHost => '0.0.0.0',
    LocalPort => $port,
    Proto => 'tcp',
    Listen => 5,
    Reuse => 1
);
die "cannot create socket $!\n" unless $socket;
print "server waiting for client connection on port $port\n";

# waiting for a new client connection
$client_socket = $socket->accept();
 
while(1)
{

    # get information about a newly connected client
    my $client_address = $client_socket->peerhost();
    my $client_port = $client_socket->peerport();
    print "connection from $client_address:$client_port\n";

    # read up to 1024 characters from the connected client
    my $data = "";
    $client_socket->recv($data, 1024);
    print "received data: $data\n";
 
    # write response data to the connected client
    $data = "ok";
    $client_socket->send($data);
 
    # notify client that response has been sent
    #shutdown($client_socket, 1);
}

##</code><code>##

PARENT: Going to transfer line -- 1 --
PARENT: Successfully pushed to child!
Connected!
CHILD: Received line -- 1 --

CHILD: $socket->send() successful: -- 1 --

CHILD: received response: ok
PARENT: Going to transfer line -- 2 --
PARENT: Successfully pushed to child!
CHILD: Received line -- 2 --

CHILD: $socket->send() successful: -- 2 --

CHILD: received response: ok
PARENT: Going to transfer line -- 3 --
PARENT: Successfully pushed to child!
CHILD: Received line -- 3 --

CHILD: $socket->send() successful: -- 3 --

CHILD: received response:
PARENT: Going to transfer line -- 4 --
PARENT: Successfully pushed to child!
CHILD: Received line -- 4 --

CHILD: error when trying to send(): send: Cannot determine peer address at test_4.pl line 70.
PARENT: Going to transfer line -- 5 --
PARENT: Successfully pushed to child!
CHILD: Received line -- 5 --

CHILD: error when trying to send(): send: Cannot determine peer address at test_4.pl line 70.
PARENT: closed writer, waiting for child to exit
Could not connect!
Died at test_4.pl line 58.

##</code><code>##

server waiting for client connection on port 7775
connection from 127.0.0.1:37480
received data: -- 1 --

connection from 127.0.0.1:37480
received data: -- 2 --

connection from 127.0.0.1:37480
^CCan't call method "close" on an undefined value at sim.pl line 8.