Mac OS® X Tiger™ Unleashed

Communication Between Processes: Redirection, Pipes

Building an operating system out of a multitude of small, cooperating processes would not provide such flexibility and power to the user were it not for a simple method of making all of these processes speak to each other. At the heart of the interprocess communications model of Unix is a simple but amazingly effective abstraction of the idea of input and output.

To paraphrase the model on which Unix bases input and output, you can imagine that Unix thinks of user input to a program as a stream—a stream of information. Output from the program back to the user can be thought of in the same way. A stream of information is simply a collection of information that flows in or out of the program in ...