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In most Linux systems, your default shell is the bash shell. To find out what is your default login shell, enter the following commands:

 $ who am i chris pts/0 2019-10-21 22:45 (:0.0) $ grep chris /etc/passwd chris:x:13597:13597:Chris Negus:/home/chris:/bin/bash

Notice that the command-line examples shown here and throughout the book show the command followed by output from that command. When the command completes, you are presented with the command prompt again.

The who am i command shows your username, and the grep command (replacing chris with your username) shows the definition of your user account in the /etc/passwd file. The last field in that entry shows that the bash shell (/bin/bash) is your default shell (the one that starts up when you log in or open a Terminal window).

It's possible, although not likely, that you might have a different default shell set. To try a different shell, simply type the name of that shell (examples include ksh, tcsh, csh, sh, dash, and others, assuming that they are installed). You can try a few commands in that shell and type exit when you are finished to return to the bash shell.

You might choose to use different shells for the following reasons:

 You are used to using UNIX System V systems (often ksh by default) or Sun Microsystems and other Berkeley UNIX-based distributions (frequently csh by default), and you are more comfortable using default shells from those environments.

 You want to run shell scripts that were created for a particular shell environment, and you need to run the shell for which they were made so that you can test or use those scripts from your current shell.

 You simply prefer features in one shell over those in another. For example, a member of my Linux Users Group prefers ksh over bash because he doesn't like the way aliases are used with bash.

Although most Linux users have a preference for one shell or another, when you know how to use one shell, you can quickly learn any of the others by occasionally referring to the shell's man page (for example, type man bash). The man pages (described later in the section “Getting Information about Commands”) provide documentation for commands, file formats, and other components in Linux. Most people use bash just because they don't have a particular reason for using a different shell. The rest of this chapter describes the bash shell.

Bash includes features originally developed for sh and ksh shells in early UNIX systems, as well as some csh features. Expect bash to be the default login shell in most Linux systems that you are using, with the exception of some specialized Linux systems (such as some that run on embedded devices) that may require a smaller shell that needs less memory and requires fewer features. Most of the examples in this chapter are based on the bash shell.