Interprocess Communication

The IPC facilities of perl are built on the Berkeley socket mechanism. If you don't have sockets, you can ignore this section. The calls have the same names as the corresponding system calls, but the arguments tend to differ, for two reasons. First, perl file handles work differently than C file descriptors. Second, perl already knows the length of its strings, so you don't need to pass that information. Here is a sample client (untested):

($them,$port) = @ARGV;
$port = 2345 unless $port;
$them = 'localhost' unless $them;

$SIG{'INT'} = 'dokill';
sub dokill { kill 9,$child if $child; }

require 'sys/socket.ph';

$sockaddr = 'S n a4 x8';
chop($hostname = `hostname`);

($name, $aliases, $proto) = getprotobyname('tcp');
($name, $aliases, $port) = getservbyname($port, 'tcp')
        unless $port =~ /^\d+$/;
($name, $aliases, $type, $len, $thisaddr) =
                                gethostbyname($hostname);
($name, $aliases, $type, $len, $thataddr) = gethostbyname($them);

$this = pack($sockaddr, &AF_INET, 0, $thisaddr);
$that = pack($sockaddr, &AF_INET, $port, $thataddr);

socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
bind(S, $this) || die "bind: $!";
connect(S, $that) || die "connect: $!";

select(S); $| = 1; select(stdout);

if ($child = fork) {
        while (<>) {
                print S;
        }
        sleep 3;
        do dokill();
}
else {
        while (<S>) {
                print;
        }
}

And here's a server:

($port) = @ARGV;
$port = 2345 unless $port;

require 'sys/socket.ph';

$sockaddr = 'S n a4 x8';

($name, $aliases, $proto) = getprotobyname('tcp');
($name, $aliases, $port) = getservbyname($port, 'tcp')
        unless $port =~ /^\d+$/;

$this = pack($sockaddr, &AF_INET, $port, "\0\0\0\0");

select(NS); $| = 1; select(stdout);

socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
bind(S, $this) || die "bind: $!";
listen(S, 5) || die "connect: $!";

select(S); $| = 1; select(stdout);

for (;;) {
        print "Listening again\n";
        ($addr = accept(NS,S)) || die $!;
        print "accept ok\n";

        ($af,$port,$inetaddr) = unpack($sockaddr,$addr);
        @inetaddr = unpack('C4',$inetaddr);
        print "$af $port @inetaddr\n";

        while (<NS>) {
                print;
                print NS;
        }
}