Hi DevOps Learners, we are back with #Day4 of the #90daysofdevops series and today we will be taking a look at the basics of Shell scripting that is needed if you are going to start your career as a DevOps engineer.

• Before deep diving into shell commands and scripting let's take a look at what is a Shell and some terms that we need to know to understand these concepts:

What is Kernel?

🌱 A kernel is like the core 🧠 of an operating system. It is the essential component that manages the system's resources and acts as a bridge 🌉 between software and hardware.

The kernel is responsible for handling tasks such as memory management 🧮, process management 🔄, device drivers 🖥️, and file system access 📂. It provides an interface for software applications to interact with the underlying hardware and ensures that different components of the system can work together harmoniously.

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What is a Shell? 🐚

• 🐚 A shell in Linux is like a friendly 🤝 intermediary between you (the user) and the operating system. It provides a command-line interface (CLI) 📜 where you can type commands and perform various tasks. It's like a virtual 🚪 doorway to the system's resources.

• There are different types of shells available, like the 🐚 Bourne Shell (sh), the widely-used 🌟 Bash (Bourne Again Shell), and the 🐚 C Shell (csh). Each has its own set of features and syntax.

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What is Linux Shell Scripting? 🐧

• 🐧 Linux shell scripting is a combination of text-based commands, special symbols, and scripting constructs to create powerful scripts that can automate tasks and unleash the potential of the command-line interface (CLI).

Please see below architectural diagram to understand the Linux architecture on how the shell, the kernel, the hardware and utilities coordinate with each other :

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

• The #!/bin/bash is called a shebang or a hashbang. It is a special construct used at the beginning of a script file to specify the interpreter or shell that should be used to execute the script. In this case, #!/bin/bash indicates that the script should be executed using the Bash shell.

• By specifying #!/bin/bash, you ensure that the script is interpreted using the Bash shell.

• While #!/bin/bash is commonly used, it is also possible to use #!/bin/sh as the shebang in your script. This indicates that the script should be executed using the default system shell, which may be a different shell than Bash.

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Write a Shell Script which prints

I will complete #90DaysOofDevOps challenge

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

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Write a Shell Script to take user input, input from arguments and print the variables :

#!/bin/bash
echo "$@"
echo "Enter the challenge day number :"
read cnumber
echo "Good, lets get started with $cnumber"

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Write an Example of If else in Shell Scripting by comparing 2 numbers:

#!/bin/bash

echo "Enter first number:"
read num1
echo "Enter second number:"
read num2

if [ $num1 -eq $num2 ]; then
        echo "Numbers are equal"
elif [ $num1 -lt $num2 ]; then
        echo " $num1 is smaller than $num2"
else
        echo " $num1 is greater than $num2"
fi

Output in Terminal :

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That's it for #day4. In the upcoming days we will be learning about topics like user management, file permissions, access control lists and many more. Till then, happy learning !!! Ciao!