What is a UNIX / Linux Shell ?

A UNIX or Linux shell is a command-line interpreter or shell that provides a traditional UNIX-like command line interface ( CLI ). 
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Logging in and starting a Unix session
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Use putty or other utility to connect to the UNIX / Linux host
•At login prompt enter the login id and then the password
•Upon entering the id/password you will get a prompt ( which is the shell prompt )
•echo $SHELL

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The commonly used Shells and the default prompts are
•sh ( Bourne Shell ) $
•ksh ( Korn Shell ) $
•csh ( C Shell ) %
•bash ( Bourne again Shell ) bash$

NOTE :

Most of the commands like grep, find, ls, cp, mv etc... are not the Shell commands. These are the utilities ( executable files ) which are installed with UNIX / Linux. Also, note that in a stricter sense, Linux is only the Kernel and GNU/Linux is the Operating System. Similarly UNIX is a registered trademark of The Open Group. The names of the operating systems are IBM AIX, HP-UX and Sun Solaris ( now called as Oracle Solaris ).

Fundamentals of UNIX / Linux ==> by Chintamani Thakur --- email : chintamani.thakur@gmail.com