I would use pipes instead of socketpairs, but mostly because I'm not really familiar with socketpairs.

The following code doesn't work on Win32, since select is (properly) implemented only for sockets on Win32. Presumably, you could use the same basic idea but with socketpairs and have it work on Win32 as well. *shrug*

#!/usr/bin/perl
use warnings;
use strict;

use IO::Handle;
use IO::Pipe;
use IO::Select;

my $stdout = IO::Pipe->new();
my $stdin  = IO::Pipe->new();

defined(my $pid = fork) or die "Fork failed\n";

if($pid) {
  $stdout->reader();
  $stdin ->writer();
  $stdin ->autoflush(1);
  my $select = IO::Select->new($stdout);
  foreach my $key (@ARGV) {
    $stdin->print("parent ($$) send [$key]\n");

    next unless $select->can_read(1);
    $stdout->sysread(my $buf, 1024);
    chomp($buf);

    print "parent ($$) recv [$buf]\n";
  }
  $stdin->close();
  waitpid($pid, 0);
} else {
  $stdout->writer();
  $stdin ->reader();
  $stdout->autoflush(1);
  open STDOUT, ">&", $stdout;
  open STDIN, "<&", $stdin;
  exec "$^X", "tst.pl";
}
[download]

And tst.pl:

#!/usr/bin/perl
use warnings;
use strict;

$|++;

while(<STDIN>) {
  chomp;
  next unless /\[(\d+)\]/ && $1 % 2 == 1; # Only odds
  print "$1 is odd\n";
}
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