Running Linux, 5th Edition - Matthias Kalle Dalheimer [75]
Some of the shells available on Linux are as follows:
bash
Bourne Again shell. The most commonly used (and most powerful) shell on Linux. POSIX-compliant, compatible with the Bourne shell, created and distributed by the GNU project (Free Software Foundation). Offers command-line editing, history substitution, and Bourne shell compatibility.
csh
C shell. Developed at Berkeley. Mostly compatible with the Bourne shell for interactive use, but has a very different interface for programming. Does not offer command-line editing, although it does have a sophisticated alternative called history substitution. On Linux, csh is just another name for the newer tcsh.
ksh
Korn shell. Perhaps the most popular on Unix systems generally, and the first to introduce modern shell techniques (including some borrowed from the C shell) into the Bourne shell. Compatible with the Bourne shell. Offers command-line editing.
sh
Bourne shell. The original shell. Does not offer command-line editing.
tcsh
Enhanced C shell. Offers command-line editing.
zsh
Z shell. The newest of the shells. Compatible with the Bourne shell. Offers command-line editing. Has very powerful completion features. If you do not know any shell yet, and your Linux distribution carries zsh, go with that choice from the start.
Try the following command to find out what your shell is. It prints out the full pathname where the shell is located. Don't forget to type the dollar sign:
$ echo
$SHELL
You are probably running bash, the Bourne Again shell, because that is the most popular one on Linux. If you're running something else, this might be a good time to change to bash or zsh. They are both powerful, POSIX compliant, well supported, and very popular on Linux. Use the chsh command to change your shell:
$ chsh
Enter password: Type your password here — this is for security's sake
Changing the login shell for mdw
Enter the new value, or press return for the default
Login Shell [/bin/sh]:/bin/bash
(Use /usr/bin/zsh or /bin/zsh, depending on your distribution, for zsh.)
Before a user can choose a particular shell as a login shell, that shell must be installed and the system administrator must make it available by entering it in /etc/shells.
There are a couple of ways to conceptualize the differences between shells. One is to distinguish Bourne-compatible shells from csh-compatible shells. This will be of interest to you when you start to program with the shell, also known as writing shell scripts. The Bourne shell and C shell have different programming constructs. Most people now agree that Bourne-compatible shells are better, and there are many Unix utilities that recognize only the Bourne shell.
Another way to categorize shells is to identify those that offer command-line editing (all the newer ones) versus those that do not. sh and csh lack this useful feature.
When you combine the two criteria—being compatible with the Bourne shell and offering command-line editing—your best choice comes down to bash, ksh, or zsh. Try out several shells before you make your choice; it helps to know more than one, in case someday you find yourself on a system that limits your choice of shells.
Useful Keys and How to Get Them to Work
When you type a command, pressing the Backspace key should remove the last character. Ctrl-U should delete the line from the cursor to the beginning of the line; thus, this key combination will delete the whole line if the cursor is at the end of the line. When you have finished entering a command, and it is executing, Ctrl-C should abort it, and Ctrl-Z should suspend