Any program is only as good as it is useful. - Linus Torvalds (Founder of Linux)

Introduction

👉 Welcome to the world of Linux, where the command line is your entryway to unlock the true power and flexibility of your computer. Whether you're an experienced sysadmin, a beginner developer, or just someone curious about the inner workings of your operating system, this comprehensive guide is your roadmap to becoming a command-line guru.

👉 Linux is a powerful and versatile operating system that offers a command-line interface for interacting with the system. These basic commands will help you navigate the file system, manage files and directories, view and edit files, gather system information, manage processes, and interact with networks.

👉 Shell scripting, on the other hand, is the art of automating tasks, simplifying complex operations, and making your computer work for you. It allows you to create powerful, repeatable processes using just a text editor and a few lines of code. Whether you want to automate system maintenance, manage files, or build custom tools, shell scripting is an invaluable skill.

Architecture of Linux

The Linux operating system's architecture mainly contains some of the components: the Kernel, System Library, Hardware layer, System, and Shell utility.

💡 Hardware Layer :

At the lowest level, Linux interacts directly with the computer's hardware which includes components such as the CPU, memory (RAM), storage devices (hard drives, SSDs), input/output (I/O) devices (keyboard, mouse, display, network cards), and more. It needs to communicate with these hardware components to manage resources effectively.

💡 Kernel:

The kernel is the core of the Linux OS and serves as an intermediary between the hardware and software layers. It is responsible for managing hardware resources, providing essential services, and providing security and access control.

💡 Shell:

The shell is like a UI to the Linux OS. It interprets user commands and executes them. There are several shells available for Linux, including Bash (Bourne Again Shell), Zsh, and others. The shell also provides features like scripting, command history, and job control.

💡User Applications:

On top of the Linux OS, users can run a wide range of applications, including web browsers, text editors, media players, development tools, and many more. These applications are designed to be compatible with the Linux environment and utilize system libraries and utilities.

Prerequisites

👉 Before using these commands, ensure you have one of the following environments set up:

• 📌 Ubuntu Desktop: Install Ubuntu on your local machine by following the official installation guide at ubuntu.com.

• 📌 Windows Subsystem for Linux (WSL): If you're using Windows, set up WSL by following the instructions in Microsoft Docs.

• 📌 Amazon EC2 Instance: If you prefer a cloud environment, create an Amazon EC2 instance running a Linux distribution. Follow the steps outlined in the AWS documentation.

Basic Linux Commands

👉 Navigating the File System

• pwd: Print the current working directory.

• ls: List files and directories in the current directory.

• cd: Change the current directory.

• cd..: Move to the previous directory.

• mkdir: Create a new directory.

• rmdir: Remove an empty directory.

• man: Manual for the Package

👉 File and Directory Operations

• cp: Copy files or directories.

• mv: Move (rename) files or directories.

• rm: Remove files or directories.

• touch: Create an empty file.

• chmod: Change file permissions.

• chown: Change file ownership.

• clear: Clear the Terminal.

👉 Viewing and Editing Files

• cat: Display the contents of a file.

• more/less: Display file contents one screen at a time.

• nano/vim: Text editors for viewing and editing files.

👉 System Information

• uname: Display system information.

• whoami: Display the name of the user.

• df: Show disk space usage.

• free: Display system memory usage.

• top: Monitor system processes in real time.

• history: Show all the used commands.

• sudo: Grant SuperUser permissions.

👉 Process Management

• ps: Display information about running processes.

• kill: Terminate processes using their process ID (PID).

👉 Network Commands

• ping: Test network connectivity to a host.

• sudo apt-get update: Update Packages of the OS.

• sudo apt-get install <Package Name>: Install Packages on the OS.

• scp: Send a file to the server.

• echo: Print the content written after the command.

• ifconfig/ip: Display network interface information.

• netstat: Show network statistics.

• ssh: Securely access remote systems. :)

Shell Scripting

💡 Shell scripting is the practice of creating and executing scripts written in a shell language, which is a command-line interface provided by an operating system. The shell is a text-based interface that allows users to interact with an operating system's services and functionalities using text-based commands. An example of a Shell Script is:

#!/bin/bash
# A simple shell script to greet the user

echo "Hello! Please enter your name:"
read name

echo "Hello, $name! Nice to meet you."

Shell Commands

The echo command prints text to the terminal.

echo "Hello, world!"

The ls command lists directory contents.

ls
ls -l   # Detailed list
ls -a   # Show hidden files

The grep command searches for text patterns within files.

grep "pattern" file.txt

The chmod command changes file permissions.

chmod +x script.sh   # Add execute permission
chmod 644 file.txt  # Change permissions numerically

The sleep command allows to sleep the program for some time.

sleep 2 # This will sleep the program for 2 seconds.

The wget command downloads files from the internet.

wget https://example.com/file.txt

Bash allows you to work with variables to store and manipulate data:

name="John"
echo "Hello, $name!"

Conditional statements help make decisions in scripts:

if [ "$num" -gt 10 ]; then
    echo "Greater than 10"
else
    echo "Less than or equal to 10"
fi

Bash can read and manipulate files:

file="example.txt"

if [ -e "$file" ]; then
    echo "$file exists."
else
    echo "$file does not exist."
fi

Loops allow you to repeat commands:

for i in {1..5}; do
    echo "Number: $i"
done # Remeber to add done at the end to exit from the loop

While Loops are the same as for loops with a different syntax and usage:

while [ condition ]; do
    # commands
done

Adding a User in Shell:

#!/bin/bash

read -p "Enter the username: " username

# Check if the user already exists
if id "$username" &>/dev/null; then
    echo "User '$username' already exists."
else
    # Prompt for user details
    read -p "Enter the full name: " fullname
    read -p "Enter the password: " password

    # Create the user with the provided details
    useradd -c "$fullname" -m "$username"
    echo "$username:$password" | chpasswd

    echo "User '$username' created successfully."
fi

Functions allow you to group commands:

greet() {
    echo "Hello from function!"
}

greet

System Commands

free

Display information about the system's memory usage

free -h

top

Interactively monitor system processes and memory usage.

top

disk free

Display information about the system's disk size and usage

df -H

AWK

Awk is a versatile text processing tool.

df -H | awk '{print $1, $3}' filename

Use awk to print specific columns from a file (e.g., column 1 and 3) from the df -H command.

Vim

Using the Vim Editor Vim is a powerful text editor for the command line.

Opening a File Open a file using Vim.

vim filename

Command Mode Basics:

• i: Enter insert mode

• Esc: Exit insert mode

• :w: Save changes

• :q: Quit Vim

• :wq: Save and quit

Conclusion

👉 In this comprehensive guide to Linux and Shell for Software Engineers, we've covered a wide range of topics essential for mastering Linux command-line usage and shell scripting. From understanding the Linux file system hierarchy and navigating directories to configuring networks, writing shell scripts, and exploring Linux Man pages, you now have a solid foundation to dive deeper into the world of Linux.

👉 Remember that practice makes perfect. The more you work with Linux commands, the more comfortable and proficient you'll become. Experiment with various commands, create shell scripts for automation and explore the vast capabilities Linux offers.

👉 For a more in-depth discussion about shell scripting, stay tuned for my upcoming blog where I'll delve into a variety of DevOps tools.

👉 With the knowledge gained from this guide and continuous exploration, you'll be well-equipped to excel as a Software Engineer working in Linux environments. Happy coding and exploring the world of Linux!