Continuing the exploration of the Linux Shell we look the various shell options you have.

1. The Shell Game 2
Kevin O'Brien
Washtenaw Linux Users Group
http://www.lugwash.org

2. Varieties of Shell
● In Linux, you always have choices, whether
you like it or not ☺
● With shells you have choices
● The Bourne-Again Shell (bash) is most likely
the default you have on your system now
● But you can use others as well

3. Why use different shells?
● Like any other choice, you would select
different shells because they have special
capabilities you want to make use of
● They may have special commands, or use
less resources, or maybe you just feel more
comfortable with one shell rather than another

4. Bourne shell (sh)
● The original Unix shell
● Written by Stephen Bourne at Bell Labs in
1974
● A simple shell, with small size and few
features
● Every Unix-like system either has sh, or has a
shell that incorporates everything in sh

5. Bourne-Again Shell (bash)
● The default for all Linux systems
● Also runs on virtually all Unix-like systems,
and there is even a version available for
Windows
● Bash is a superset of sh, that is, it
incorporates everything that is in sh, but then
adds to it
● It is very flexible, and a good choice for
beginners. The rest of this series will use bash
to illustrate using a shell.

6. Almquist Shell (ash)
● Basically a clone of sh
● Very small memory requirements
● Thus it is useful for small embedded systems

7. C Shell (csh)
● Created by Bill Joy while he was at UC
Berkeley
● Syntax very similar to the C programming
language

8. Korn shell (ksh)
● Developed by David Korn at Bell Labs in 1983
● Superset of SH, with many features of the C
Shell as well
● Advanced scripting capabilities similar to what
is in awk, sed, and perl

9. TENEX C Shell (tcsh)
● Based on C Shell
● Adds features not found in C Shell
● Now the default shell on some BSD systems
(FreeBSD and Darwin)

10. Z Shell
● Written by Paul Falstad around 1990
● Simlar to ksh, but has features from csh as
well
● Attempt to use the programmability of the ksh
with csh features

11. You can choose
● You can make a temporary switch of your
shell
● Or you can change the default if you find one
you like better

12. Temporary switch
● A shell is an executable file (everything in
Linux is a file)
● So you just run it
● For example, to change to the original Bourne
shell, just type “sh” at the prompt
● To go back to the Bourne-Again shell, just
type “bash” at the prompt
● When you change, notice that the prompt itself
looks different

13. Changing the default 1
● Suppose you find a shell you like better, and
you want that to be the shell you always want
to see when you boot up your computer
● First, find out the full path of the shell, i.e.,
what is the full path, starting from the root, to
the executable file that contains the shell
● To get clues, open up /etc/shells and
etc/passwd
● For example, bash is usually /bin/bash

14. Changing the Default 2
● Once you know the full path to the shell you
now want to be the default, use the change
shell command (chsh)
● This will open a brief dialog to make the
change, and will ask you for your password to
authorize it

15. Whose shell is this, anyway?
● One thing you need to remember is that the
choice of shell is only being made for the
person logged in
● You could have multiple users on a system,
and have each one make their own shell
choice
● Tip: always try out a shell temporarily before
making a permanent change