In this lesson, you will be introduced to the Linux Command Line Interface (CLI), an essential tool for interacting with Unix/Linux-based operating systems. You will learn what the CLI is, its advantages, and how to get help using the command line.

What is the Command Line Interface (CLI)?

The Command Line Interface, often referred to as the CLI or terminal, is a text-based interface for interacting with a computer's operating system. It allows users to issue commands to the computer by typing text-based instructions rather than using a graphical user interface (GUI). The CLI is a powerful and efficient way to control and manage a Unix/Linux system.

Advantages of Using the CLI

Why would you want to use the CLI when you have a graphical desktop environment available? Here are some advantages:

1. Efficiency: The CLI is often faster for experienced users to perform tasks.
2. Scripting and Automation: You can create scripts to automate repetitive tasks.
3. Resource Efficiency: The CLI consumes fewer system resources than a GUI.
4. Remote Access: You can access and manage remote servers over a network.

Commandline

When you first enter the shell session you will see output like the following:

paulh@ubuntu-server:~$

Let's break it down:

• paulh: This is the username of the current user who is logged into the system.
• @: This symbol separates the username from the hostname.
• ubuntu-server: This is the hostname of the computer or server. In this example, the system is named "ubuntu-server."
• ~: The tilde character represents the current user's home directory. In Unix/Linux systems, the tilde (~) is a shorthand notation for the home directory of the currently logged-in user. In this case, it indicates that the user "paulh" is in their home directory.
• $: The dollar sign ($) is the command prompt symbol. It signifies that the command line is ready to accept input from the user. You can enter commands after the prompt to interact with the system.

If I use the cd (change directory) command to /home, we can see the updated prompt below:

paulh@ubuntu-server:~$ cd /home
paulh@ubuntu-server:/home$

Now you will notice between the (:) and ($) characters, we see our current path, which is now /home. To go back to our home directory, we can type the (~) character:

paulh@ubuntu-server:/home$ cd ~
paulh@ubuntu-server:~$

Getting Help

One of the first things you should know when working with the CLI is how to get help. Here are two common methods:

1. Using the man Command

The man command (short for "manual") provides detailed documentation for most commands and topics on a Unix/Linux system. To use it, simply type man followed by the name of the command you want to learn more about. For example:

man ls

This command will display the manual page for the ls command, which is used for listing files and directories.

2. Using --help or -h

Many commands support a --help or -h option that provides a brief overview of the command's usage and available options. For example:

ls --help

This will display a list of options and a short description of the ls command's functionality.

3. Using the info Command

The info command is another tool for accessing documentation on Unix/Linux systems. It provides more extensive and structured documentation for various topics, including commands. To use it, simply type info followed by the topic or command you want to learn more about. For example:

info ls

This will open the documentation for the ls command in the info viewer.

4. Using the ls Command

You can also use the ls command to explore directories and get a quick overview of what's inside. For instance, to list the contents of the /bin directory, you can run:

ls /bin

This command will display a list of executable files and programs located in the /bin directory. Try running the info or man command against some of the executable files (designated with an asterisk *) in the /bin directory.

Conclusion

The Linux Command Line Interface is a powerful and versatile tool for interacting with your Unix/Linux-based system. In the following lessons, we will explore various aspects of the CLI, including file system navigation, creating and manipulating files, and using text editors like Nano and Vi. As you progress, you'll unlock the full potential of the command line and gain valuable skills for managing and administering Unix/Linux systems.

Now that you have a basic understanding of what the CLI is and its advantages, you also know how to seek help when you encounter unfamiliar commands or need guidance on their usage. This ability to access documentation and assistance is a valuable skill in the world of Linux and Unix systems.