Linux comes with quite a few shells such as Bourne Shell, Bourne Again Shell, C Shell, Korn Shell, etc. The default shell for Red hat Linux is ‘ bash ‘ which is very popular since being the default, most users start by learning bash. I shall talk about the bash shell only in this article.
Typing the following at the shell
$ echo $SHELL
would give you the name of the current shell you are using. It would most probably be the bash shell in case you are a new user and have been assigned the default shell.
The bash shell is actually a program that is located at /bin/bash and is executed by Linux the moment a user successfully logs in after entering his user-pass. Once this shell starts, it takes over control and accepts all further user commands. The bash shell presents a $ prompt by default (for normal user accounts). You can change this prompt to whatever you like but leaving it at the default is best.
All the programs that run under Linux are called as processes. Processes run continuously in Linux and you can kill or suspend different processes using various commands. When you start a program a new process is created. This process runs within what is called an environment. This particular environment would be having some characteristics which the program/process may interact with. Every program runs in its own environment. You can set parameters in this environment so that the running program can find desired values when it runs.
Setting a particular parameter is as simple as typing VARIABLE=value . This would set a parameter by the name VARIABLE with the value that you provide.
To see a list of the environment variables that are already set on your machine, type the following
This would produce a long list. Just go through the list before reading the next part of the article. Linux by default sets many environment variables for you. You can modify the values of most of these variables. A few of the variables that are set are