Recording-2025-09-18T00:45:49.525Z

Overview of the Linux Shell

The Linux shell is a command line interface (CLI) that enables text-based interaction between the user and the operating system.
It is a program that runs commands you type and returns the output, acting as the intermediary between you and the OS.
The shell is especially powerful for system administration and scripting; while a GUI may be more approachable for beginners, the shell offers deeper functionality and automation.
This material focuses on the Bash shell, but also mentions other shells in general.

When you log in, the first directory you land in is your home directory.
Home directories live under /home and are named after the user; e.g., Michael and Alan.
- Michael's home directory: \text{/home/Michael}
- Alan's home directory: \text{/home/Alan}
The home directory is private by default; other users cannot access your files or folders without permission.
A home directory stores personal data in files and directories; think of it as a dedicated locker for each user.
The home directory is represented by the tilde symbol (~) in the command line prompt and in path abbreviations.
The prompt shown can be configured to display different information (host name, date, time, etc.); in the example, it shows the current working directory.
The tilde (~) expands to the home directory in many shell environments; you can use it in commands, e.g., \text{cd ~} goes to the home directory.
The concept of the home directory can be summarized as: the home directory path is \text{/home/username} and the symbol \sim represents it.
Why the home directory matters: it provides a private space for each user to store personal data and configurations.

Interaction with the shell happens by typing commands; the shell executes a program and returns its output.
The echo command prints a line of text to the screen.
If you run echo with no arguments, it prints nothing because there is no input to echo.
An argument is input to a command; for example, using echo hello prints the word "hello" on a new line.
Many commands require arguments to function, but some work without any arguments (e.g., uptime).
Commands can have options (also called switches or flags) that modify their behavior. Options are typically a single letter preceded by a single hyphen; e.g., the -n option for echo prevents printing a trailing newline.
Because there are many options, it is common to consult help or the manual pages for unfamiliar commands.
Help sources include inline help (often via -h or --help) and the manual pages (man pages).
The document introduces the idea that you will learn more about help options and man pages later in the course.

Linux commands fall into two broad categories: internal (built-in) commands and external commands.
Internal commands are part of the shell itself and come bundled with it.
There are approximately 30 built-in commands.
Examples of built-in commands mentioned in the transcript include: cd (change directory), export, and pwd (print working directory). The transcript also lists mkdir (make directory) as a built-in in that context, and it mentions uptime as an example that does not require arguments.
External commands are binary executables or scripts located in standard filesystem locations (e.g., /bin, /usr/bin). They are usually installed by the distribution's package manager or can be created/installed by the user.
To determine whether a command is internal or external, use the type command.
Example from the transcript: echo is a shell built-in, while mv is an external command.

When working with unfamiliar commands, refer to built-in help or online documentation:
- Inline help: use command -h or