What is Shell Script
A shell script is a list of commands in a computer program that is run by the Unix shell which is a command-line interpreter. A shell script usually has comments that describe the steps. 

Allow you to run if-else statements and loops.
A file that contains a series of commands.
A plain text file.
It executes the command on each line, one line at a time.
The terminal usually allows just one command at a time.
Shell script allows you to combine and run multiple commands together


When do we need a shell script?
You need to enter multiple shell commands and you will need to do it again in the future.
If you know how a piece of work need to perform.. you can put that knowledge in a shell script
ShellScript eliminates repetitive tasks through automation.
Using a good script can reduce the change of error.
A shell script can perform a task faster than a human can.
You have to do a task more than once, but it's something that you rarely do.