what is shell in linux

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Shell is a UNIX term for the interactive user interface with an operating system. The shell is the layer of programming that understands and executes the commands a user enters. In some systems, the shell is called a command interpreter. A shell usually implies an interface with a command syntax (think of the DOS operating system and its "C:>" prompts and user commands such as "dir" and "edit").

•          The shell is a user program or it is an environment provided for user interaction.
•          It is a command language interpreter that executes commands read from the standard input device such as keyboard or from a file.
•          The shell gets started when you log in or open a console (terminal).
•          Quick and dirty way to execute utilities.
•          The shell is not part of system kernel, but uses the system kernel to execute programs, create files etc.
•          Several shells are available for Linux including:
•          BASH ( Bourne-Again SHell ) - Most common shell in Linux. It's Open Source.
•          CSH (C SHell) - The C shell's syntax and usage are very similar to the C programming language.
•          KSH (Korn SHell) - Created by David Korn at AT & T Bell Labs. The Korn Shell also was the base for the POSIX Shell standard specifications.
•          TCSH - It is an enhanced but completely compatible version of the Berkeley UNIX C shell (CSH).
Please note that each shell does the same job, but each understands different command syntax and provides different built-in functions. Under MS-DOS, the shell name is COMMAND.COM which is also used for the same purpose, but it is by far not as powerful as our Linux Shells are!
Shell Prompt
There are various ways to get shell access:
•          Terminal - Linux desktop provide a GUI based login system. Once logged in you can gain access to a shell by running X Terminal (XTerm), Gnome Terminal (GTerm), or KDE Terminal (KTerm) application.
•          Connect via secure shell (SSH) - You will get a shell prompt as soon as you log in into remote server or workstation.
•          Use the console - A few Linux system also provides a text-based login system. Generally you get a shell prompt as soon as you log in to the system.



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