Piping output between two simultaneous, independent programs

Question

Let's say I have two programs which play chess: chess_1 and chess_2. They keep track of the board themselves, and take as input opposing moves, and then output their moves. For example, if I wanted to play against chess_1, I would do the following:

I would start the program (assuming I am white)

$ ./chess_1                  # program starts and hangs for input
  <my move>                  # my input
  <the bot's move>           # bot output
  <my next move>             # my input
.... < etc. > .....

And the bot would keep track of the game board. My question is, how can I make chess_1 play against chess_2?

In other words, you means tie stdout of `chess1` to stdin of `chess2` and vice versa? For a start I would say you should be allowing the move to be specified through `stdin` rather than via a command line argument. After that, why not just use named pipes? — Wildcard, Apr 19 '16 at 01:54
@Wildcard I think so. Honestly I know that this information exists out there, but I really had no idea what it was called so I was having a hard time finding it. I'll look for "named pipes". (I also changed i/o to stdin int eh question) — Liam, Apr 19 '16 at 01:56
They're also called `fifo`s (for "first in first out"); that may help. The tool to create them is `mkfifo` but the man page assumes you already know what they are. :) Here's an [Introduction to Named Pipes](http://www.linuxjournal.com/article/2156). — Wildcard, Apr 19 '16 at 01:57

score 1 · Answer 1 · edited Apr 13 '17 at 12:37

You did not specify the shell, so, in general, named pipes would be easiest way. However, if your shell supports them, this could be a nice use case for coprocesses.

How do you use the command coproc in Bash?

In a | cmd | b, a feeds data to cmd and b reads its output. Running cmd as a co-process allows the shell to be both a and b.

In bash:

coproc ./chess_1
./chess_2 < "${COPROC[0]}" > "${COPROC[1]}"

The linked post also talks about drawbacks of coprocesses, and has examples of using named pipes (via mkfifo).

Piping output between two simultaneous, independent programs

1 Answers1