Motivation

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A shell is a program that sits between you and the raw Linux operating system. There are three shells that are commonly used by Linux usersthe Bourne Again shell (bash), the Korn shell (ksh), and the C shell (tcsh). All of these shells share a common core set of operations that make life in the Linux system a little easier. For example, all shells allow the output of a process to be stored in a file or "piped" to another process. They also allow the use of wildcards in filenames, so it's easy to say things like "list all of the files whose name ends with the suffix '.c'." This chapter describes all of the common core shell facilities, and subsequent chapters describe the special features of each individual shell.