Learning Red Hat Linux, Third Edition

Working with the Linux Command Prompt

Linux commands share a simple, common structure. This section describes their common structure and explains how you can obtain helpful information about the commands available to you.

Commands and Arguments

The general form of a shell command line is this:

               command [options] [arguments]

The command determines what operation the shell will perform and the options and arguments customize, or fine-tune, the operation. The options and arguments may or may not appear, as indicated by the square brackets. Sometimes the command specifies a program file that will be launched and run; such a command is called an external command . Linux generally stores these files in /bin, /usr/bin, or /usr/local/bin. System administration commands are generally stored in /sbin or /usr/sbin, which are included by default in the path of the root user. When a command specifies a program file, the shell passes any specified arguments to the program, which scans and interprets them, adjusting its operation accordingly.

Some commands are not external program files; instead they are built-in commands interpreted by the shell itself. One important way in which shells differ is in the built-in commands that they support. Later in this section, you’ll learn about some of bash’s built-in commands.

The name of a Linux command almost always consists of lowercase letters and digits. Most commands let you specify options or arguments. However, in any given case, you may not need ...