IN THIS CHAPTER
What is a shell?
Why use the command line?
Working with files and directories
Understanding Linux permissions
Getting help for Linux commands
How to configure the bash shell
Because Linux has its conceptual roots in the older UNIX operating system, many Linux applications are executed from a command line. A command line is the traditional interface found on older computer systems that may not have used the high-resolution, graphically oriented monitors that most people expect today. In the command-line model, the system runs a program, known as a command-line interpreter, which does just what its name suggests: It reads the commands that you type, locates the appropriate application on your system, and executes that application for you as instructed based on what you've typed. Once the command completes, the command interpreter displays a sequence of characters, known as a prompt, signifying that it is ready to accept another command.
Linux systems aren't reliant on the command-line approach simply out of historical interest—when a Linux system boots, it needs to be able to run several commands long before the graphical interface is available. On Linux systems, the graphical interface itself is started by a command-line utility, after which (of course) fancy graphics are available, expected, and used.
For most people, simply displaying a command-line prompt on a fancy graphical monitor powered by a multi-megabyte graphics card would be ...