Electronic mailing lists provided communities where people with like interests could exchange messages. These lists were closed systems, in the sense that only subscribers could post messages to the list or view messages posted by other subscribers. Obviously, lists grew and list managers had to maintain them. Over time, automated mechanisms were developed to allow people to subscribe (and, even more importantly, to unsubscribe) without human intervention. These mailing lists evolved into message forums, where people could publicly post messages on an electronic bulletin board for everyone to read.

Thanks also to my parents and to Celia’s parents for their love and support. Rich Rosen We would both like to thank the following people for their help:• our editor, Jonathan Shipley, and his assistants, Georgia King and Claire Jardine, for their professionalism and flexibility throughout the project; • our technical reviewers, Sue Fitzgerald, Ciaran O’Leary, Ilmi Yoon, Roger Beresford, Yuanzhu Peter Chen, Ray Cheung and Wei Ding, for taking the time to examine the text and provide us with valuable insights and advice; • our colleagues, Otis Gospodnetich and Keith Kim, for their comments and suggestions for the search chapter, and Heow Eide-Goodman for his comments and suggestions for the chapters on development approaches and Rails application development.

Command-line programs have their origins in the limitations of the oldest human interface to computer systems: the teletype keyboard. In the earliest days of computing, even simple text-based CRT terminals were not available - let alone today’s monitors with advanced graphics capabilities. The only way to enter data interactively was through a teletypewriter interface, one character at a time. A command-line interface (CLI) prompts the user for the entry of a “command” (the name of a program) and its “arguments” (the parameters passed to the program).