Mac OS X (pronounced "Mac OS Ten"), the latest incarnation of the Macintosh operating system, is a radical departure from previous versions. Not only is there a whole new look and feel on the surface, there are also huge differences under the hood. All the old, familiar Macintosh system software has been replaced with another operating system, called Unix. Unix is a multiuser, multitasking operating system. Being multiuser means Mac OS X allows multiple users to share the same system, each having the ability to customize their desktop, create files that can be kept private from other users, and make settings that will automatically be restored whenever that person uses the computer. Being multitasking means Mac OS X can easily run many different applications at the same time, and that if one application crashes or hangs , the entire system doesn't need to be rebooted.
The fact that Mac OS X is Unix under the hood doesn't matter to users who simply want to use its slick graphical interface to run their applications or manage their files. But it opens up worlds of possibilities for users who want to dig a little deeper. The Unix command-line interface, which is accessible through a Mac application in the Utilities folder called Terminal, provides an enormous amount of power for intermediate and advanced users. What's more, once you've learned to use Unix in Mac OS X, you'll also be able to use the command line in other versions of Unix or the Unix-compatible Linux.
This book is designed to teach the basics of Unix to Macintosh users. We tell you how to use the command line (which Unix users refer to as "the shell") and the filesystem, as well as some of the most useful commands. Unix is a complex and powerful system, so we scratch only the surface, but we also tell you how to deepen your Unix knowledge once you're ready for more.