Many different Unix shells are available on Mac OS X Tiger. This book describes the bash shell. The Bourne-Again shell (bash), which is based on the Bourne shell (sh). bash is the most commonly used shell for many other Unix variants, including most Linux distributions and FreeBSD.
Most Unix systems have more than one shell, and it's not uncommon to use one shell for writing scripts and another for interactive use. Other popular shells included with Mac OS X Tiger can be found in the /bin directory and are available to all users on the system.
You can change to another shell by typing the program name at the command line. For example, to change from bash to tcsh, type:
To switch back to bash, just exit tcsh
exit # or ^D