use Socket;

my ($kidfh, $dadfh);
socketpair($kidfh, $dadfh, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
   or die "socketpair: $!";

my $oldfh;

$oldfh = select $kidfh;
print STDOUT $oldfh, "\n";
$oldfh = select $dadfh;
print STDOUT $oldfh, "\n";