I am new to socket programming. I would like to program a PHP script to open up a UNIX domain socket (AF_UNIX) to communicate with another program running on the system. I've Googled to see how to accomplish this, however all I can really find are examples of internet sockets (AF_INET) for simple TCP/IP programs.

Can anyone help me figure out UNIX sockets with PHP or direct me to a good reference for UNIX sockets with PHP?

You might find starting here to be useful, there's at least 1 example of AF_UNIX plus plenty of links to defs/examples.
http://au2.php.net/manual/en/ref.sockets.php

Incidentally, I wrote a system that runs 24/7 with co-operating processes and had probs making UNIX sockets robust/graceful enough in error handling, so used INET sockets instead and it works just fine. (Actually in Perl, but the principles are the same).
YMMV ...

This is one of the pages that turned up in my Google search. I think the TCP/IP client/server examples are handy for learning the AF_INET way of doing things, but I was hoping to see an example that uses AF_UNIX. (I searched the page for an example that uses AF_UNIX instead of AF_INET but couldn't find one...may you're seeing something I'm not?)

Coincidentally, I would like to pass messages between a php process and a perl process. What sorts of issues did you face with UNIX sockets that were solved by switching to INET sockets?