Linux Shell Scripting: Automate Like a Pro! 🚀

Now that you’ve mastered the core Linux concepts, it’s time to take the next big leap—Shell Scripting! 🖥️💡

🔹 Why Learn Shell Scripting?
Shell scripting is a must-have skill for DevOps, automation, system administration, and cloud computing. It helps you:
✅ Automate repetitive tasks
✅ Manage system configurations efficiently
✅ Perform bulk operations in a single command
✅ Improve productivity & minimize human errors

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1️⃣ What is Shell Scripting?

A shell script is a file containing a series of commands that the Linux shell executes sequentially. Instead of running commands one by one, you can put them in a script and run them automatically!

📌 Basic Structure of a Shell Script:

#!/bin/bash
echo "Hello, DevOps World!"   # Prints a message

• #!/bin/bash → Shebang, tells Linux to use the Bash shell
• echo → Prints text to the screen

🔹 Running a Shell Script:
1️⃣ Create a script file: nano myscript.sh
2️⃣ Make it executable: chmod +x myscript.sh
3️⃣ Run the script: ./myscript.sh

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2️⃣ Variables & User Input in Shell Scripts

🔹 Defining Variables:

name="DevOps Engineer"
echo "Hello, $name!"

🔹 User Input:

echo "Enter your name:"
read user_name
echo "Welcome, $user_name!"

🔹 Environment Variables:

echo "Your home directory is: $HOME"

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3️⃣ Conditional Statements: Decision Making in Shell

🔹 If-Else Condition:

#!/bin/bash
echo "Enter your age:"
read age

if [ $age -ge 18 ]; then
    echo "You are eligible to vote!"
else
    echo "Sorry, you are not eligible."
fi

🔹 Case Statements:

echo "Enter a number between 1-3:"
read num
case $num in
    1) echo "You chose One!";;
    2) echo "You chose Two!";;
    3) echo "You chose Three!";;
    *) echo "Invalid choice!";;
esac

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4️⃣ Loops: Automating Repetitive Tasks

🔹 For Loop:

for i in 1 2 3 4 5
do
   echo "Number: $i"
done

🔹 While Loop:

count=1
while [ $count -le 5 ]
do
   echo "Iteration: $count"
   ((count++))
done

🔹 Until Loop:

x=1
until [ $x -gt 5 ]
do
   echo "Number: $x"
   ((x++))
done

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5️⃣ Functions in Shell Scripting

Functions allow code reuse and better script structure.

#!/bin/bash

function greet() {
    echo "Hello, $1! Welcome to Linux Scripting!"
}

greet "DevOps Engineer"

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6️⃣ File Handling in Shell Scripts

🔹 Checking if a file exists:

if [ -f /etc/passwd ]; then
    echo "File exists!"
else
    echo "File does not exist!"
fi

🔹 Reading a file line by line:

while read line; do
    echo "$line"
done < myfile.txt

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7️⃣ Process Management in Shell Scripts

🔹 Killing a process:

#!/bin/bash
echo "Enter process name to kill:"
read pname
pkill $pname

🔹 Monitoring CPU & Memory Usage:

echo "Top 5 CPU-consuming processes:"
ps -eo pid,comm,%cpu --sort=-%cpu | head -6

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8️⃣ Scheduling Jobs with Crontab

Want to run scripts automatically at a scheduled time? Use Crontab!
🔹 Opening Crontab Editor:

crontab -e

🔹 Scheduling a script to run every day at midnight:

0 0 * * * /path/to/script.sh

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9️⃣ Real-World Shell Scripting Examples

🔹 Automating Backup Process:

#!/bin/bash
tar -czf backup_$(date +%F).tar.gz /home/user/documents
echo "Backup completed!"

🔹 Checking Server Uptime & Health:

#!/bin/bash
echo "System Uptime:"
uptime
echo "Disk Usage:"
df -h
echo "Memory Usage:"
free -m