# Linux Series: Bash Programming & Operating Systems (Part-2) # Overview * Welcome to part 2 of our Linux Fundamentals series! In this section, we will be exploring Ubuntu, one of the most popular Linux distributions. * Throughout this part, we will be diving into the command line interface, a powerful tool that allows you to interact with the system using text commands. * We'll be covering some of the most useful and commonly used commands in Linux, helping you to build your knowledge and confidence. # Starting the Terminal 1. What Is A Terminal? * A terminal, also known as a command-line interface (CLI) or console, is a text-based interface used to interact with a computer's operating system. * It provides a way for users to issue commands and receive output directly from the system. * Many experienced users prefer the terminal because it allows for more precise control and can automate repetitive tasks using scripts. * Additionally, some tasks can only be performed through the terminal, making it an essential tool for system administration and software development. 2. What Is A Shell? * A shell is a program that provides an interface between the user and the operating system, enabling users to interact with the system through the command line interface (CLI) or terminal. * When a user enters a command in the terminal, the shell interprets that command and executes it on behalf of the user. * The shell is responsible for managing the input and output of commands, as well as handling things like environment variables, user permissions, and command history. * Most of the shells by default use bash as their programming language. 3. Bash Programming * Bash (Bourne-Again Shell) is a popular shell in Linux and Unix-based operating systems. It's not only a powerful tool for interacting with the system but also a versatile programming language. * Overall, Bash programming is a useful skill for anyone who wants to work with Linux systems, automate tasks, or perform system administration tasks. With its simple syntax and powerful capabilities, Bash is a versatile tool that can help you achieve your goals efficiently and effectively. 4. Shell Format * Most of the shells that are out there they have the following format ```bash username@hostname:~ $ ``` ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1677698525707/60edc5fa-ded6-4f88-b836-1f83fef7ac07.png align="center") # Structure and Tree Hierarchy of Directory [📁](https://emojipedia.org/file-folder/) * Let's understand this with images, ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1677698570351/60decbdc-3606-46fe-8266-90eb4ca62b59.png align="center") ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1677698589474/0a47e61e-48db-441d-a7d7-48638b2e6910.png align="center") ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1677698599204/9253f42e-b154-4514-bef0-ddfee29f249c.png align="center") * Now, visually you are familiar with the Structure and Tree Hierarchy of Directory. # Exploring Commands [💻](https://emojipedia.org/laptop/) * First, let's print "Hello World" into the console using Bash. > echo Hello World! * `Relative Path and Absolute Path`\- Relative path specifies the location of a file or directory relative to the current working directory, whereas an absolute path specifies the exact location of a file or directory from the root directory. * This is a very important topic, let me explain it to you with an amazing story, * Let's understand it, In Linux, each directory or folder is like a room and every room is a path. * The path guides you in reaching the directory, whether from the "home" directory or the current directory you're currently in. So here comes two paths, absolute and relative. * An **absolute** path is like giving the exact address of a room, starting from the front door of the building. * It includes the entire path from the root directory all the way to the destination directory. * For example, the absolute path to the "Bootcamp" folder in the "home" directory might be: ```bash /home/username/Bootcamp ``` * A relative path, on the other hand, is like giving directions to a room from your current location. * It only includes the path from the current directory to the destination directory. * For example, if you're already in the "home" directory, the relative path to the "Bootcamp" folder might be: ```bash Bootcamp ``` * This is because the "Bootcamp" folder is located in the "home" directory, which is your current directory. * Let's start exploring. 1. `pwd` - It stands for "print working directory" which is the directory or folder that the user is currently in within the file system hierarchy. 2. `ls` - This command lists the files and directories in the current directory. 3. `cd` - This command changes the current working directory to the specified directory. 4. `mkdir` - This command creates a new directory. 5. `mkdir -p` - This command creates a new directory and any necessary parent directories. 6. `touch` - This command creates a new empty file. 7. `gedit a.txt` - This command opens the file "a.txt" in the Gedit text editor. 8. `file` - This command provides information about the type of a file. 9. `cat` - This command displays the contents of a file. 10. `history` - This command displays a list of previously executed commands. 11. Navigating History (up and down-button) - These keys are used to navigate through the command history. 12. `Ctrl + C` - This key combination interrupts the currently running process. 13. `Ctrl + r` - This key combination searches the command history for a previously executed command. 14. Autocomplete (tab) - This key is used to autocomplete commands and file/directory names. 15. `cp` - This command copies files or directories from one location to another. 16. `mv` - This command moves files or directories from one location to another. 17. `rm` and `rmdir` - These commands delete files and directories, respectively. 18. `rm -r` - This command recursively deletes all files and directories in the specified directory. 19. `rm -rv` - This command recursively deletes all files and directories in the specified directory and provides verbose output. 20. `find` - This command searches for files and directories that match specified criteria. 21. `man` - This command displays the manual page for a specified command. 22. `whatis COMMAND` \- The `whatis` command is useful when you're not sure what a particular command does or want to quickly find out what a new command you've discovered does. * example: `whatis ls` ```bash ls(1) - list directory contents ``` # Flags 🏴 * In Bash, flags are also referred to as options or switches. They are additional parameters that can be passed to a command to modify its behavior. Let's see some Flags:: 1. `.` : This flag represents the current directory. * For example, `ls .` would list the contents of the current directory. 2. `..` : This flag represents the parent directory of the current directory. It is often used to move up one level in the directory hierarchy. For example, `cd ..` would move the user up one level in the directory hierarchy. 3. `~` : This flag represents the user's home directory. It is often used to refer to the home directory of the current user. * For example, `cd ~/Desktop` would change the current directory to the Desktop folder in the user's home directory. 4. `-` : This flag represents the previous directory. It is often used to quickly switch between two directories. * For example, `cd -` would switch the user to the previous directory they were in. 5. `/` : This flag represents the root directory of the file system. It is often used to refer to the top-level directory in the file system hierarchy. * For example, `ls /` would list the contents of the root directory. # **You can find me on these platforms** [**🤝**](https://emojipedia.org/handshake/) **:** > ***After reading this blog, give your reviews and feedbacks for more improvements.*** * [**Twitter**](https://twitter.com/MuhammadN_twts) * [**Linkedi**](https://www.linkedin.com/in/muhammadnoorani)n * [**GitHub**](https://github.com/MuhammadNoorani) * [**Blog**](https://blog.muhammadnoorani.com/)