🐚 What is Shell Scripting?

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💬 Definition

Shell scripting is the practice of writing a series of commands for the shell (command-line interpreter) to execute automatically. These commands are written in a plain text file, which is referred to as a shell script.

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📦 What is a Shell?

A shell is a program that provides a text-based interface for users to interact with the operating system.

Popular shells include:

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📜 What is a Shell Script?

A shell script is a file that contains a sequence of shell commands that are executed in order.

Example:

bash

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#!/bin/bash

echo "Starting backup..."

tar -czf backup.tar.gz /home/user

echo "Backup complete."

🔍 What’s Happening Here?

●  #!/bin/bash: Tells the system to use the Bash shell.

● echo: Prints messages to the screen.

● tar: Compresses the /home/user directory into a .tar.gz file.

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🎯 Why Use Shell Scripting?

Shell scripting is used to:

● ✅ Automate repetitive tasks (backups, updates, deployments)

● ✅ Configure system settings

● ✅ Run multiple commands as a single program

● ✅ Schedule jobs with tools like cron

● ✅ Quickly test logic or prototypes

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🛠️ Real-Life Examples

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🧠 Key Characteristics of Shell Scripts

● Plain text files (.sh)

● Run using bash scriptname.sh or ./scriptname.sh

● Start with a shebang (#!/bin/bash) to specify the interpreter

● Can use:

○ **Variables

○ Conditions* (if, else)*

○ Loops (for, while)

○ **Functions

○ Command substitution* ($(command))*

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🧪 Example: Simple Script

bash

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#!/bin/bash

echo "Welcome to Shell Scripting"

date

uptime

This script:

1. Greets the user

2. Shows the current date

3. Displays how long the system has been running

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💡 Summary

🧠 Introduction to Bash Syntax

(For Shell Scripting Beginners)

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🧾 1. Variables in Bash

Variables are used to store data for reuse. In Bash, you don’t need to declare a type (everything is treated as a string unless used in arithmetic).

🔧 Syntax

bash

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variable_name=value

⚠️ No spaces before or after the equal sign.

🧪 Example

bash

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name="DevOps Student"

echo "Welcome, $name!"

🔍 Output

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Welcome, DevOps Student!

📥 2. User Input

Use the read command to take input from the user.

🧪 Example

bash

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#!/bin/bash

read -p "Enter your name: " username

echo "Hello, $username!"

🔍 What’s Happening?

●  read -p: Prompts the user and stores input in a variable.

●  $username: Prints what the user entered.

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📤 3. Output (echo)

The echo command displays text or variables.

🧪 Example

bash

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echo "Welcome to Bash scripting"

You can also format text:

bash

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echo -e "Line 1\nLine 2"

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❓ 4. Conditional Statements

Bash uses if, then, else, and fi to control decision-making.

🧪 Example

bash

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#!/bin/bash

read -p "Enter username: " user

if [ "$user" == "admin" ]; then

  echo "Access granted"

else

echo "Access denied"

fi

🔍 Breakdown:

● [ "$user" == "admin" ]: Checks if user is "admin"

●  then: Executes block if true

● else: Executes if false

● fi: Ends the if statement

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🔁 5. Loops

Loops help automate repetitive tasks.

🔁 For Loop

bash

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for i in {1..5}

do

  echo "Iteration $i"

done

🔁 While Loop

bash

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count=1

while [ $count -le 3 ]

do

  echo "Count is $count"

  ((count++))

done

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🧩 6. Functions

Functions allow you to reuse blocks of code.

🧪 Example

bash

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greet() {

  echo "Hello, $1"

}

 greet "DevOps Engineer"

● $1 is the first argument to the function.

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⚙️ 7. Command Substitution

You can run a command and use its output in a variable.

🧪 Example

bash

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current_date=$(date)

echo "Today is $current_date"

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🛡️ 8. Exit Status ($?)

Every command returns a status code: 0 = success, non-zero = failure.

🧪 Example

bash

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ls /some/folder

echo "Exit status was $?"

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✅ Summary Table

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🧠 Your First Task

Write a script that:

1. Asks for the user’s name

2. Greets them

3. Shows the current date and uptime

Example structure:

bash

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#!/bin/bash

read -p "Enter your name: " name

echo "Hi, $name!"

echo "Today is: $(date)"

echo "System uptime:"

uptime

See the outcome result below