A Word of Caution

The command-line interface is an incredibly powerful tool, and that power comes with the potential for doing accidental damage to your files. In the Mac OS X graphical interface, if you make a mistake, you can usually choose Edit > Undo (Command-Z) to backtrack, and destructive actions usually are accompanied by dialogs requesting confirmation. There are no such safety nets with the command-line interface. If you enter the wrong command, you might delete documents or render the computer inoperable with no warning, and you will be able to undo the damage only by restoring your system from a backup or reinstalling Mac OS X.

The commands in this lesson's exercises are relatively harmless if entered as shown. But you should still be careful as you follow along with this lesson, and don't experiment unless you know exactly what you are doing.