[barhun]

+ "On UNIX, the adage goes, everything is a file."

- not all the things on unix are abstracted as files (or 'byte streams' to be more accurate). however, i/o resources and some ipc facilities are defined so. an operating system provides many other abstractions in addition to these such as processes, threads, non-stream devices, concurrency and synchronization primitives, etc.; thus it's absolutely wrong to say that everything is a file on unix.

[qubex]

Most notably: network sockets do not have file-like semantics, mainly because they were introduced as a concept and implemented long after the system was designed. Plan9 is an effort to revise all system objects to be accessible with the same file-like fopen/fclose system calls.

[RJIb8RBYxzAMX9u]

"Everything is a file on UNIX" is as true as "Vulcan's cannot lie."

[sh_tinh_hair]

Great analogy.

[na85]

I assume Vulcans can lie?

[LeoPanthera]

Technically they cannot lie. But they can exaggerate. Or omit facts.

[sh_tinh_hair]

Only one ipc primitive (fifo) can be used with man 2 read or write. Sysv ipc cannot, sockets (any domain) cannot (unless there is a kernel interface via /proc or another pseudo fs). What is meant by this saying (and the way it is has been used in my experience) is that everything in unix _looks_ like a file. That is usually meant in reference to the C API which has some r[ec]v|read|write|snd type namespace.

[deathanatos]

You can read(2) and write(2) to a socket, although it is more normal to recv and send on it. On Linux, you can also (and pretty much MUST) read(2) and write(2) to an eventfd; you can read(2) from a timerfd. That said, the semantics of the latter are considerably different from that of fifos or sockets.

[sh_tinh_hair]

You are right. I've long forgotten about read() and write() compat with sockets for very good reason. I don't lump an eventfd into the same IPC category as those mentioned in parent for the semantic(s) reason you mention and also for it's intended usage.

[darfs]

Could this provide an example please?

Only for those like me, who are wondering...^^