IN THIS CHAPTER
Most programs have a user interface (UI) of some kind. In fact, depending on exactly how you define user interface, you could say that all programs have a user interface.
For instance, if the program is one that executes as a daemon process, the user interface is the set of command line options available for the user to start the daemon, either manually or through an automated script. The program's error message reporting mechanism is also part of the interface; does it log messages to a file, print them on the console, or beep at the user?
Nowadays, we tend to think of user interfaces as interfaces ...