Shell Scripting Basics: Uses, Benefits, and Examples

INTRODUCTION

Normally, shells are interactive—meaning the shell accepts commands from you via the keyboard and executes them immediately. However, if you store a sequence of commands in a text file and instruct the shell to execute that file, it becomes a shell program or shell script. A shell script is essentially “a series of command(s) stored in a plain text file.” It’s similar to a batch file in MS-DOS but far more powerful. Shell scripts are a core part of the UNIX and Linux programming environments.

They are essential for automating tasks, managing systems efficiently, and building simple utilities.

Why shell scripting ?

You can use shell scripts to easily do tasks that you repeat each time you open the prompt.

You can supply input to a shell script through either a user or a file and the script will show the results on the screen
When you find yourself doing something multiple times, it’s time to use shell scripting which improves repetitive task automation.
Creating your own power tools/utilities.
Automating command input or entry.
Customizing administrative tasks.
Creating simple applications.
Because scripts are thoroughly tested, you are less likely to make mistakes during system administration tasks or configuring services.

Practical examples where shell scripting actively used

Monitoring your Linux system.
Data backup and creating snapshots.
Doing a backup of your Oracle or MySQL database.
Creating email based alert system
See which goblin-like processes are taking up your system resources
Find out available and free memory.
See the users on the system and find out what they are up to.
Determine if every required network service is operating or not. As an example, if the web server fails, automatically let the system admin know by sending an email or a pager.
If many unsuccessful login attempts are made from the same IP address, block that IP from using your network/service by using firewall.
Watch over user administration as you choose for your security policies.
Check what local and remote servers are available in your network.
Set up a server called BIND (DNS server) to add zone entries.

There is a lot of fun in shell scripting. Making things in shell scripting that look good (or even bad sometimes) can help you improve your skills. Below are some scripts that I use commonly everyday:

Find out today’s weather (useful when you are busy in a chat room)
Find out what that site is running (just like net craft).
Download RSS feeds and display them as you login or in your email.
Find out the name of the MP3 file you are listening to.
Monitor your domain expiry date every day.

Advantages

Easy to use.
Quick start, and interactive debugging.
Time Saving.
Sys Admin task automation
Almost any modern UNIX / Linux / BSD / Mac OS X operating system can run shell scripts because they are written in an interpreted language.

Disadvantages

Compatibility problems between different platforms.
Slow execution speed.

Each shell command usually causes a new process to start.

Conclusion:

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