Question

I have two processes that interface with one another over stdin and stdout.

Suppose I have process A and process B. The stdout of B needs to feed into the stdin of A, and the stdout of A needs to feed in to that of process B.

Is there a simple way to express this relationship in a simple command, or is there a basic shell script that can enable this?

Thanks in advance.

Answer 1

Take a look at named pipes. Create one pipe for A to B, and one pipe for B to A. Then start A with its stdout redirected to the first, and its stdin redirected to the second. Then start B with the opposite.

It would look something like this:

mkfifo --mode=0666 /tmp/AtoB
mkfifo --mode=0666 /tmp/BtoA
A < BtoA > AtoB
B < AtoB > BtoA

add: Of course, they’ll need some way to recognize that both parties are present. Something like a simple “I am here, are you?” that both receive a response to.

Important: As noted in comments below, this process will deadlock with both programs blocking on reads. Some form of coordination will be necessary to ensure this doesn’t happen.