## 6.2. Shell Flavors

Many different Linux shells are available. This book describes the three most popular shells:

- The Bourne-Again shell (bash), which is based on the Bourne shell (sh) and is standard for Linux

- The C shell (csh), which uses C syntax and has many conveniences

- tcsh, an extension of csh that appears instead of csh in many Linux distributions

Most systems have more than one shell, and people will often use one shell for writing shell scripts and another for interactive use.

When you log in, the system determines which shell to run by consulting your entry in /etc/passwd. The last field of each entry calls a program to run as the default shell. For example:

Program Name | Shell
/bin/sh | Bourne-Again shell
/bin/bash | Bourne-Again shell
/bin/csh | C shell (or tcsh)
/bin/tcsh | tcsh

You can change to another shell by typing the program name at the command line. For example, to change from bash to tcsh, type:

>     $ exec tcsh

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