A shell script is a script written for the shell, or command line interpreter, of an operating system. The shell is often considered a simple domain-specific programming language. Typical operations performed by shell scripts include file manipulation, program execution, and printing text.

Normally shells are interactive. It means shell accept command from you (via keyboard) and execute them. But if you use command one by one (sequence of 'n' number of commands) , the you can store this sequence of command to text file and tell the shell to execute this text file instead of entering the commands. This is know as shell script.

Shell script defined as:
"Shell Script is series of command written in plain text file. Shell script is just like batch file is MS-DOS but have more power than the MS-DOS batch file."

Advantages

• Shell script can take input from user, file and output them on screen.
• Useful to create our own commands.
• Save lots of time.
• To automate some task of day today life.
• System Administration part can be also automated.

It includes the following topics -

• Shell types and BASH shell
• BASH shell variables, commands and scripting
• Editors