Shell Scripting Basics | Automation

Introduction

Shell scripting is a powerful tool in the Linux environment that allows users to automate tasks, manage system operations, and streamline workflows. This tutorial will guide you through the basics of shell scripting, from simple commands to writing full scripts.

What is a Shell?

A shell is a command-line interpreter that provides a user interface for the Unix operating system. The most common shell is Bash (Bourne Again SHell).

Creating Your First Script

To create a shell script, you simply create a text file with the commands you want to execute. Let's start with a simple example:

#!/bin/bash
echo "Hello, World!"

Save this file as hello.sh and make it executable by running the following command:

chmod +x hello.sh

Now you can run your script:

./hello.sh

Hello, World!

Variables

Variables in bash are used to store information that can be referenced later in the script.

#!/bin/bash
NAME="John"
echo "Hello, $NAME"

Hello, John

Conditional Statements

Bash supports conditional statements like if-else to perform different actions based on conditions.

#!/bin/bash
if [ "$1" -gt 100 ]
then
echo "The number is greater than 100"
else
echo "The number is less than or equal to 100"
fi

Loops

Loops allow you to iterate over a series of commands. The two most common types are for and while loops.

For Loop

#!/bin/bash
for i in 1 2 3 4 5
do
echo "Welcome $i times"
done

Welcome 1 times
Welcome 2 times
Welcome 3 times
Welcome 4 times
Welcome 5 times

While Loop

#!/bin/bash
COUNTER=0
while [ $COUNTER -lt 5 ]
do
echo "Count: $COUNTER"
COUNTER=$((COUNTER + 1))
done

Count: 0
Count: 1
Count: 2
Count: 3
Count: 4

Functions

Functions are used to group commands into a single, reusable unit. They make scripts easier to read and maintain.

#!/bin/bash
function greet {
echo "Hello, $1"
}
greet "Alice"
greet "Bob"

Hello, Alice
Hello, Bob

Conclusion

This tutorial covered the basics of shell scripting, including creating scripts, using variables, conditional statements, loops, and functions. With these fundamentals, you can start automating tasks and improving your productivity in the Linux environment.