What is a Shell

The user who uses a UNIX OS may know English. However the kernel, the heart of the OS, which processes the user request could not understand the normal English, and will know only machine language. So there should a mediator between the user and kernel to translate the language between them. In UNIX related Operating systems, shell is the utility which will do this task. That is, when the user enters the commands to shell prompt, the shell will accept the same and will interpret to kernel, the meaning of the same. The kernel will understand the same and will process the data and will revert to shell with the results. The same results will be conveyed to user by the shell in human readable form. In other words, Shell the interpreter between User and Kernel (The Usual definition).


Below are the common shells available in UNIX.

1. Bourne Shell – sh

2. Bourne again shell – bash

3. Korn Shell – ksh

4. C Shell – csh

1. How to know your current shell?

You can issue the below command to find out the current working shell.

#echo $SHELL

Here, SHELL is an environment variable.

2. How to change your current shell?

You can change the current shell by executing the below command.

#chsh

You can change the login shell in /etc/passwd also.