How to write a 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 "Hello World" on screen (As we do it all programming languages; I always wonder why?? :P)  See the common vi command list , if you are new to vi

$ vi first # # My first shell script # clear echo "Hello World"  <br>


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

First screen will be cleared, then Hello World is printed on screen.

Let me know if you need more details or explanation on any particular topics in Shell scritping.