$pid = open(KID_TO_WRITE, "|-");
    if ($pid) {  # parent
        print KID_TO_WRITE @some_data;
        close(KID_TO_WRITE) || warn "kid exited $?";
    } else {     # child
        while (<STDIN>) {
            ...
            print ; # child's STDIN is parent's KID
        }
        exit;  # don't forget this
    }