DevOps Day#4:-Basic Linux Shell Scripting for DevOps Engineers

If you've ever felt overwhelmed doing the same tasks over and over again on your computer, Linux shell scripting might be your new best friend. It's a superpower for automating tasks, especially in the world of DevOps! Let’s dive into the basics of Linux shell scripting, understand its role in DevOps, and create some beginner-friendly scripts.

What is a Kernel?

The kernel is the heart of an operating system. Think of it as the bridge between your computer's hardware and the software you run. It handles tasks like:

• Managing memory.

• Running programs.

• Communicating with hardware (like your CPU and disk).

Without the kernel, your computer wouldn’t know how to execute even the simplest command.

What is a Shell?

A shell is like a translator between you (the user) and the kernel. It lets you give instructions (commands) to your computer in a way it understands. There are different types of shells, like:

• Bash (Bourne Again Shell) – The most popular shell in Linux.

• Sh (Bourne Shell) – A simpler, older version of Bash.

When you type commands like ls or pwd, the shell processes them and sends them to the kernel to execute.

What is Shell Scripting?

Shell scripting is writing a series of shell commands in a file, called a script, to automate tasks. Instead of typing commands one by one, you write them once, and the computer runs them for you.

Benefits of Shell Scripting

1. Automation: Saves time by handling repetitive tasks.

2. Efficiency: Performs complex tasks quickly and consistently.

3. Flexibility: Combines commands to create powerful workflows.

4. Crucial for DevOps: Automates deployments, manages servers, and handles CI/CD pipelines.

Shell Scripting in DevOps

In DevOps, shell scripting is indispensable. It helps:

• Automate server provisioning and deployments.

• Set up and manage CI/CD pipelines.

• Monitor logs and system performance.

Example: Imagine you need to deploy an application to 10 servers. Instead of doing it manually, a shell script can deploy it to all servers with a single command.

Task 1: Explain in your own words and with examples what Shell Scripting means for DevOps.

Shell Scripting is writing a series of commands in a script file to automate tasks in the Unix/Linux shell. For DevOps, shell scripting is crucial for automating repetitive tasks, managing system configurations, deploying applications, and integrating various tools and processes in a CI/CD pipeline. It enhances efficiency, reduces errors, and saves time.

Example: Automating server setup for installing apache2 software

• Create a file “automation.sh” in your Linux machine.

• Open your file and write script given below image.

  

• Give permission for make it executable.

•   chmod +x automation.sh
  

• Run this file ./file name .

    ./automation.sh
  

• Then final output you will get Apache server installation done. Check bellow image:

Task 2: What is #!/bin/bash? Can we write #!/bin/sh as well?

• #!/bin/bash is called a "shebang" line. It indicates that the script should be run using the Bash shell.

  • #!/bin/bash: Uses Bash as the interpreter. It supports advanced features like arrays, associative arrays, and functions.

  • #!/bin/sh: Uses the Bourne shell. It’s more POSIX-compliant and is generally compatible with different Unix shells.

Task 3: Write a Shell Script that prints I will complete #90DaysOfDevOps challenge.

Steps:

1. Save the script as devops.sh.

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

2. Make it executable: chmod +x devops.sh

3. Run the script : ./devops.sh

   

   Output:

I will complete #90DaysOfDevOps challenge.

Task 4: Write a Shell Script that takes user input, input from arguments, and prints the variables.

Steps:

1. Save the script as input.sh.

2. Make it executable: chmod +x devops.sh

3. Run the script with argument:

    ./input.sh siba  Anand
   

   4 . Final output:

Task 5: Provide an example of an If-Else statement in Shell Scripting by comparing two numbers.

Let’s compare two numbers using an if-else statement.

Script:

Steps:

1. Save the above script as ifelse.sh.

2. Make it executable:

    chmod +x ifelse.sh
   

3. Run the script:

    ./ifelse.sh
   

4. Output:

Step-by-Step Explanation of the If-Else Script

1. Define Variables: num1 and num2 are assigned values.

2. If Condition: [ $num1 -gt $num2 ] checks if num1 is greater than num2.

3. Else Statement: Executes when the condition is false.

“With practice, you'll unlock its full potential and confidently tackle even complex tasks.”