Send messages to program through command line

Question

I have this program, we'll call it Host. Host does all kinds of good stuff, but it needs to be able to accept input through the command line while it's running. This means it has to somehow send its other process data and then quit. For example, I need to be able to do this:

./Host --blahblah 3 6 3 5

This should somehow end up calling some function in Host called

handleBlahBlah(int x1, int y1, int x2, int y2){
  //do some more sweet stuff
}

Host is a C program, and does not need to support multiple instances.

An example of this is Amarok music player. With Amarok running and playing, you can type "amarok --pause" and it will pause the music.

I need to be able to do this in Linux or Windows. Preferably Linux.

What is the cleanest way to implement this?

Answer 1

If you were on Windows, I'd tell you to use a hidden window to receive the messages, but since you used ./, I assume you want something Unix-based.

In that case, I'd go with a named pipe. Sun has a tutorial about named pipes that might be useful.

The program would probably create the pipe and listen. You could have a separate command-line script which would open the pipe and just echo its command-line arguments to it.

You could modify your program to support the command-line sending instead of using a separate script. You'd do the same basic thing in that case. Your program would look at it's command-line arguments, and if applicable, open the pipe to the "main" instance of the program, and send the arguments through.

Answer 2

If it needs to be cross-platform, you might want to consider making the running instance listen on a TCP port, and have the instance you fire up from the command-line send a message to that port.