Typically shells are interactive. It means shell accept command from you (through keyboard) and execute them. Anyhow, on the off chance that you use command one by one (arrangement of “n” number of commands), you can store this succession of command to content file and advise the shell to execute this text document as opposed to entering the commands. This is know as shell script.
Shell script defined as:
“Shell Script is arrangement of command written in plain text document. Shell script is much the same as bacth file is MS-DOS yet have more power than the MS-DOS Batch document.”
A shell script is a succession of commands for which you have a repeated use. This succession is regularly executed by entering the name of the script on the command line. On the other hand, you can utilize scripts to computerize assignments using the cron facility. Another use for scripts is in the UNIX boot and shutdown system, where operation of daemons and services are defined in init scripts.
Anything you can keep running on the command line you may put into a script and they will carry on exactly the same. The other way around, anything you can put into a script, you may keep running on the command line and again it will perform exactly the same.
At whatever point you discover yourself doing likewise undertaking again and again you ought to utilize shell scripting, i.e. repetitive task automation.
Making your own particular force tools/utilities.
Automating command input or entry.
Customizing administrative tasks.
Creating simple applications.
Since scripts are well tested, the chances of error are decreased while arranging services or system administration task, for example, including new user.
Why to write Shell Script ?
Shell script can take info from user, record and output them on screen.
Valuable to make our own commands.
Save lots of time.
To computerize some task of day today life.
System Administration part can be likewise computerized.
Easy to use.
Give your script a sensible name that gives an indication about what the script does. Verify that your script name does not clash with existing command. With a specific end goal to ensure that no confusion can rise, script names frequently end in .sh; even thus, there may be different scripts on your system with the same name as the one you picked.
Step by step instructions to compose shell script
Taking after steps are obliged to compose shell script:
(1) Use any editor like vi or mcedit to write shell script.
(2)In the wake of composing shell script set execute authorization for your script as takes after:
# chmod permission your-script-name
# chmod +x your-script-name
# chmod 755 your-script-name
(3) Execute your script as
# bash your-script-name
# sh your-script-name
# bash bar
# sh bar
NOTE: In the last structure ./ implies current directory, But just . (dot) means execute given command line in current shell without beginning the new duplicate of shell, The structure for . (dot) command is as per the following