What are named pipes?

Question

What are they and how do they work?

Context happens to be SQL Server

Answer 1

Named pipes in a unix/linux context can be used to make two different shells to communicate since a shell just can't share anything with another.

Furthermore, one script instantiated twice in the same shell can't share anything through the two instances. I found a use for named pipes when coding a daemon that contains the start() and stop() function, and I wanted to use the same script to perform the two actions.

Without named pipes (or any kind of semaphore) starting the script in the background is not a problem. The thing is when it finishes you just can't access the instance in background.

So when you want to send him the stop command you just can't: running the same script without named pipes and calling the stop() function won't do anything since you are actually running another instance.

The solution was to implement two pipes, one READ and the other WRITE when you start the daemon. Then make him, among its other tasks, listen to the READ pipe. Then the Stop() function contains a command that will write a message in the pipe, that will be handled by the background running script that will perform an exit 0. This way our second instance of the same script has only on task to do: tell the first instance to stop.

This way one and only one script can start and stop itself.

Of course you have different ways to do it by triggering the stop via a touch for example. But this one is nice and interesting to code.