use strict;
use warnings;
use IPC::Open2;

$|=1;   # this is for main program
        # $writer is alread unbuffered by open2
my $pid = open2(my $reader, my $writer, "perl echo2.pl");
print "pid=$pid\n";

for ( qw(first second third) )
{
   print $writer "$_\n";   # one line in, one line out
   my $result = <$reader>;
   print $result;
}

=heading #### echo2.pl #####
#!/usr/bin/perl -w
use strict;

$|=1;
while (my $in=<STDIN>){print $in;}
print STDERR "out of loop\n";  #never gets here!
=cut  #### echo2.pl #####

__END__
C:\TEMP>perl ipc_open2.pl
pid=3244
first
second
third