Perl Cookbook, 2nd Edition

Chapter 15. Interactivity

And then the Windows failed—and then I could not see to see

—Emily Dickinson, “I heard a Fly buzz—when I died”

Introduction

Everything we use has a user interface: VCRs, computers, telephones, even books. Our programs have user interfaces: do we have to supply arguments on the command line? Can we drag and drop files into the program? Do we have to press Enter after every response we make, or can the program read a single keystroke at a time?

This chapter won’t discuss designing user interfaces: entire bookshelves are filled with books written on the subject. Instead, we focus on implementing user interfaces—parsing command-line arguments, reading a character at a time, writing anywhere on the screen, and writing a graphical user interface.

The simplest user interface is what we are called line mode interfaces. Line mode programs normally read entire lines and write characters or entire lines. Filters like grep and utilities like mail exemplify this type of interface. We don’t really talk much about this type of interface in this chapter, because so much of the rest of the book does.

A more complex interface is what is called full-screen mode. Programs such as vi, elm, and lynx have full-screen interfaces. They read single characters at a time and can write to any character position on the screen. We address this type of interface in Recipe 15.4, Recipe 15.6, Recipe 15.9, Recipe 15.10, and Recipe 15.11.

Still more complex are the graphical user interfaces (GUIs). ...