Linux Shell Scripting and Basic commands

Title: Day 3 Task: Basic Linux Commands and Introduction to Shell Scripting for DevOps

Introduction: In the world of DevOps, having a solid understanding of Linux commands and shell scripting is essential. Linux commands enable efficient file management, system control, and automation, while shell scripting allows for the execution of multiple commands in a systematic and automated manner. In this blog post, we will explore basic Linux commands and delve into the fundamentals of shell scripting, along with examples to help you grasp the concepts.

Basic Linux Commands:

To view what's written in a file: The cat command is used to display the contents of a file. For instance: cat example.txt will show the contents of the file example.txt.
To change the access permissions of files: The chmod command is used to modify file permissions. For example, to give the owner read, write, and execute permissions, you can use: chmod u=rwx file.txt.
To check which commands you have run till now: The history command displays a list of previously executed commands, showing the command history.
To remove a directory/folder: The rmdir command is used to remove an empty directory. For example: rmdir directory_name will delete the specified directory.
To create a fruits.txt file and view the content: The touch command is used to create a file. To create fruits.txt, you can use: touch fruits.txt. To view its contents, use the cat command.
To add content in devops.txt (One in each line): You can use the echo command to add content to a file. For example:
```
 echo "Apple" >> devops.txt
 echo "Mango" >> devops.txt
 echo "Banana" >> devops.txt
```
To show only the top three fruits from the file: The head command can be used to display the first few lines of a file. For example: head -n 3 fruits.txt will display the top three lines.
To show only the bottom three fruits from the file: The tail command is used to display the last few lines of a file. For instance: tail -n 3 fruits.txt will show the bottom three lines.
To create another file Colors.txt and view the content: Use the touch command to create the Colors.txt file: touch Colors.txt. Then use the cat command to view its contents.
To find the difference between fruits.txt and Colors.txt files: The diff command is used to compare and find differences between two files. For example: diff fruits.txt Colors.txt will display the differences, if any.

Introduction to Shell Scripting for DevOps: Shell scripting involves writing computer programs to automate tasks and perform operations within a Linux shell. It allows for the execution of a series of commands in a sequential manner. Shell scripts can handle file manipulation, program execution, and printing of text. They provide flexibility, efficiency, and repeatability in automating tasks.

#!/bin/bash vs. #!/bin/sh: The #!/bin/bash is called a shebang or hashbang and specifies the interpreter (in this case, Bash) that should be used to execute the script. Bash is the default shell on most Linux distributions and provides extended functionality.

Alternatively, #!/bin/sh specifies the generic Bourne shell. While it is compatible with Bash, it may lack some advanced features. Choosing between the two depends on the specific requirements of the script and the desired compatibility.

Shell Script Examples:

Shell Script to print "I will complete #90DaysOfDevOps challenge":

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

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

 #!/bin/bash
 read -p "Enter your name: " name
 echo "Hello, $name!"
 echo "Argument 1: $1"
 echo "Argument 2: $2"

Example of if-else in Shell Scripting by comparing two numbers:

 #!/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

Conclusion: Mastering basic Linux commands and understanding shell scripting is crucial for DevOps professionals. With a solid foundation in Linux commands, you can efficiently manage files, directories, and permissions. Shell scripting empowers you to automate tasks, execute commands sequentially, and enhance your productivity. Embrace these skills, explore advanced features, and embark on your DevOps journey with confidence. Happy scripting!

Linux Shell Scripting and Basic commands

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