use IO::Handle qw( );  # For autoflush

BEGIN {
   # Override pipe to return something selectable on Windows.
   if ($^O eq 'MSWin32') {
      require Win32::Socketpair;
      require subs;
      subs->import('pipe');
      *pipe = sub {
         ($_[0], $_[1]) = Win32::Socketpair::winsocketpair()
            or return;
      };
   }
}

pipe(my $r, my $w)
   or die $!;

$w->autoflush(1);

print $w ("Hello World\n");
print(scalar(<$r>));