How to write shell script

Following steps are required to write shell script:
(1) Use any editor like vi or mcedit to write shell script.
(2) After writing shell script set execute permission for your script as follows
syntax: 
chmod permission your-script-name
Examples:
$ chmod +x your-script-name
$ chmod 755 your-script-name
Note: This will set read write execute(7) permission for owner, for group and other permission is read and execute only(5).
(3) Execute your script as
syntax: 
bash your-script-name
sh your-script-name
./your-script-name
Examples:
$ bash bar
$ sh bar
$ ./bar
NOTE In the last syntax ./ means current directory, But only . (dot) means execute given command file in current shell without starting the new copy of shell, The syntax for . (dot) command is as follows
Syntax:
. command-name
Example:
$ . foo



Now you are ready to write first shell script that will print "Knowledge is Power" on screen. See the common vi command list , if you are new to vi.

$ vi first # # My first shell script # clear echo "Knowledge is Power"

After saving the above script, you can run the script as follows:
$ ./first

This will not run script since we have not set execute permission for our script first; to do this type command
$ chmod 755 first
$ ./first