Most of the time, we interact with computers using a graphical user interface, or GUI. We click on icons, drag windows, and use menus. But there's another way to control a computer: the shell. The shell is a command-line interface (CLI) that lets you type commands directly to the operating system.

This direct control is incredibly powerful. While a GUI is great for everyday tasks, the shell excels at automation and performing complex operations with just a few lines of text. To start scripting, you first need to get comfortable in this environment.

Linux offers several different shells, each with slightly different features. Some popular ones include the Z Shell (Zsh), the Korn Shell (Ksh), and the Bourne Again Shell (Bash).

Bash is the most common and is the default shell on most Linux distributions. Because it's so widespread, we'll be focusing on Bash. The commands and concepts we cover are fundamental and will work in most other shells as well.

When you open a terminal, you're placed in a specific location within the computer's file system, called a directory. Let's learn the basic commands for finding your way around.

First, how do you know where you are? The pwd command, short for "print working directory," tells you your current location.

To see what files and directories are in your current location, use the ls command, which stands for "list."

Now, let's move somewhere else. The cd command, for "change directory," allows you to navigate. To move into the Documents directory, you would type:

If you run pwd again, you'll see your location has changed. To go back up one level, you can use two dots (..) as the destination.

You can also create and remove directories. The mkdir command makes a new directory, and rm removes files or directories. Be careful with rm! Once something is deleted with this command, it's usually gone for good.

The Linux file system is organized like a tree, starting from a single root directory, represented by a forward slash (/). Every file and folder on the system is located somewhere under this root.

Here are a few important directories:

• /: The root directory. Everything starts here.
• /bin: Contains essential command-line programs.
• /etc: Holds system configuration files.
• /home: Where user directories are located. Your personal files are typically stored in /home/your_username.
• /usr: Contains user-installed software and libraries.

Linux is a multi-user system, which means it needs rules about who can access what. These rules are called permissions. Every file and directory has permissions set for three types of users:

1. Owner: The user who created the file.
2. Group: A collection of users who share permissions.
3. Others: Everyone else.

There are three basic permissions: read (r), write (w), and execute (x). You can view permissions using the -l option with the ls command.

The string of characters at the beginning, like -rw-r--r--, represents the permissions. The first character indicates the type (- for a file, d for a directory). The next nine characters are three sets of rwx permissions for the owner, group, and others, respectively.

Understanding these basics of the shell, navigation, and permissions is the first step toward becoming proficient with the Linux command line and writing powerful scripts.