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17.6.1. Problem

Use domain sockets. You can use the code and techniques from the
preceding Internet domain recipes, with the following changes:

Unix domain sockets have names like files on the filesystem. In fact,
most systems implement them as special files; that's what Perl's
-S filetest operator looks for—whether the
file is a Unix domain socket.

Supply the filename as the Peer argument to
IO::Socket::UNIX->new, or encode it with
sockaddr_un and pass it to
connect. Here's how to make server and client Unix
domain stream sockets with IO::Socket::UNIX:

use IO::Socket;
unlink "/tmp/mysock";
$server = IO::Socket::UNIX->new(LocalAddr => "/tmp/mysock",
Type => SOCK_STREAM,
Listen => 5 )
or die $@;
$client = IO::Socket::UNIX->new(PeerAddr => "/tmp/mysock",
Type => SOCK_STREAM,
Timeout => 10 )
or die $@;

Here's how to use the traditional functions to make stream sockets:

use Socket;
socket(SERVER, PF_UNIX, SOCK_STREAM, 0);
unlink "/tmp/mysock";
bind(SERVER, sockaddr_un("/tmp/mysock"))
or die "Can't create server: $!";
socket(CLIENT, PF_UNIX, SOCK_STREAM, 0);
connect(CLIENT, sockaddr_un("/tmp/mysock"))
or die "Can't connect to /tmp/mysock: $!";

Unless you know what you're doing, set the protocol (the Proto
argument to IO::Socket::UNIX->new and the last
argument to socket) to 0 for PF_UNIX sockets. You
can use both SOCK_DGRAM and SOCK_STREAM types of communication in the
Unix domain, with the same semantics as we saw for Internet sockets.
Changing the domain doesn't change the characteristics of the socket
type.

Because many systems actually create a special file in the
filesystem, you should delete the file before you try to bind the
socket. Even though there is a race condition (somebody could create
a file with the name of your socket between your calls to
unlink and bind), this isn't a
security problem, because bind won't overwrite an
existing file.