Linux provides two user interfaces: the graphical user interface (GUI) hosted by X and an older, command-line interface (CLI) called the shell.
Those who're familiar with the MS-DOS command-line interface will recognize the shell, which you use by typing text commands to which the system responds by displaying text replies. But the comparison with the MS-DOS command line doesn't do justice to the Linux shell, which is vastly more powerful. And, older doesn't necessarily imply inferior.
GUIs are stylish primarily because they're easy to learn and use. But they're not always the most efficient way of operating a computer. A skilled user of the shell can often outrace a competitor using a GUI. Moreover, a GUI enables its user to perform only the functions the GUI's programmers provided. In contrast, the shell is expandable. The shell enables users to define entirely new operations based on sequences of existing operations.
The real power of Linux lies in the shell. So, if you aspire to master Linux, you must conquer the shell. Even if your ambition falls short of gurudom, you'll find knowledge of the shell helpful. Many procedures from sources other than this book assume that you know how to use the shell. And, if X fails, you can't easily repair it without knowing how to use the shell.
Linux supports a variety of shells, but the most popular is the bash shell, described in this chapter. The chapter explains how to issue shell commands, and how to use shell commands to manipulate files and directories, work with removable media, and launch programs. The chapter also explains pico, a simple text editor that operates in text mode.