Understanding what background processes are (see last week's tip), and how to create them should make it easier for you to grasp the concept of co-processes.

Co-processes, sometimes called co-routines, consist of two or more processes programmed to run simultaneously, and typically communicate with each other.  The parent program (script) will start a command or program in the background that is able to have two-way communication with it.  In more technical terms, the standard input and output of the background program is connected to the parent program with a pipe.  There may also be scenarios when you want more than one background program communicating with the parent program.

Co-processes are useful if you want to provide an interface to existing/legacy programs, but even more important, it is possible to improve the performance of a program by using co-processes.

The next part of this series will introduce the syntax for starting and communicating with a co-process, and will also include a simple example to demonstrate the concept.