🚀 Basic Linux Shell Scripting for DevOps Engineers

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🖥️ What is a Shell Script?

Imagine you own a pizza shop 🍕, and every day you have to:

1️⃣ Open the shop 🏪
2️⃣ Turn on the oven 🔥
3️⃣ Prepare the dough 🍞
4️⃣ Make pizza 🍕
5️⃣ Serve customers 🛎️
6️⃣ Clean the shop 🧹

Now, instead of doing this manually every single day, what if you could create a robot assistant 🤖 that follows a list of instructions and does it for you?

That’s exactly what a shell script does for computers!

✅ A shell script is like a to-do list 📋 for your computer.
✅ It tells the computer what to do step by step.
✅ It automates boring, repetitive tasks so you can relax. 😎

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🔹 What is #!/bin/bash?

The first line of a shell script starts with shebang (#!), which tells the computer which language to use for the script.

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

✔️ /bin/bash → Uses the Bash shell (most common).
✔️ /bin/sh → Uses a more general shell (might behave differently on some systems).

Think of it like telling your robot assistant which language to speak before giving instructions! 🤖

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✍️ Shell Script to Print a Message

Let's create a simple script that prints a motivational message.

#!/bin/bash
echo "I will complete #90DaysOfDevOps challenge."

📌 Save the file as challenge.sh and run:

chmod +x challenge.sh  # Give execute permission
./challenge.sh         # Run the script

Output:

I will complete #90DaysOfDevOps challenge.

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🔢 Script to Take User Input & Arguments

#!/bin/bash
echo "Enter your name:"
read name
echo "Hello, $name!"

echo "Script Name: $0"
echo "First Argument: $1"
echo "Second Argument: $2"

📌 How to run the script with arguments:

./script.sh DevOps Enthusiast

Output:

Enter your name:
Ana
Hello, Ana!
Script Name: script.sh
First Argument: DevOps
Second Argument: Enthusiast

Explanation:

• $name → Stores user input.

• $0 → The script name.

• $1, $2, etc. → Arguments passed when running the script.

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🔄 If-Else Statement in Shell Scripting

#!/bin/bash
num1=10
num2=20

if [ $num1 -gt $num2 ]
then
    echo "$num1 is greater than $num2"
else
    echo "$num1 is less than or equal to $num2"
fi

📌 Comparison Operators:

• -eq → Equal to

• -ne → Not equal to

• -gt → Greater than

• -lt → Less than

• -ge → Greater than or equal to

• -le → Less than or equal to

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🔁 Loops in Shell Scripting

Loops help us repeat tasks automatically instead of writing the same commands multiple times.

1️⃣ For Loop 🌀

A for loop is used when we know how many times we want to repeat something.

#!/bin/bash
for i in 1 2 3 4 5
do
  echo "Iteration number: $i"
done

📌 Run this script, and it will print:

Iteration number: 1
Iteration number: 2
Iteration number: 3
Iteration number: 4
Iteration number: 5

🔹 Real-life example:
Imagine you want to print 100 invoice copies. Instead of clicking print 100 times, a loop does it for you!

2️⃣ While Loop 🔄

A while loop runs until a condition is met.

#!/bin/bash
count=1

while [ $count -le 5 ]
do
  echo "Count: $count"
  count=$((count+1))  # Increase count by 1
done

📌 Output:

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

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🌍 Real-Life Use Cases for Shell Scripting

✔️ 📦 Automate software deployment → No more clicking buttons manually!
✔️ 📊 Log Analysis → Scan logs for errors and send alerts automatically.
✔️ ☁️ Cloud Automation → Start/stop cloud servers when needed.
✔️ 💾 Database Backups → Save important data without forgetting.

Just like a robot assistant makes your life easier in the pizza shop, a shell script makes life easier for DevOps engineers!