#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11123397
use warnings;
use Socket;

my $child;      #filehandle to child process
my $parent;     #filehandle to parent process
my $pid;        #Process ID of child process

socketpair($child, $parent, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
                                                or die "socketpair: $!";
$child->autoflush(1);
$parent->autoflush(1);

if ($pid = fork())
  {
  close $parent  or die "close: $!\n";
  sleep 1;
  print STDOUT time%1000, ": polling child\n";
  my $buf = '';
  while( sysread $child, $buf, 4096, length $buf )
    {
    while( $buf =~ s/(.*)\n// )
      {
      print STDOUT time%1000, ": received <$1>\n";
      }
    }
  print STDOUT time%1000, ": end of input from child\n";
  wait;
  }
elsif( defined $pid ) 
  {
  close $child or die "close: $!\n";
  print STDOUT time%1000, ": child started\n";
  sleep 5;
  print $parent time%1000, ": child printed\n";
  close $parent  or die "close: $!\n";
  exit;
  }
else
  {
  die "cannot fork: $!";
  }