Learn the Command Line Interface (CLI)

Introduction

There are two major interfaces that we use to interact with our computers. The most common interface is the graphical user interface, or GUI. This interface largely emphasizes non-textual interaction, such as the mouse, fingers (touch screens), remote controls (e.g., smart TVs), and most recently, wearable tech such as VR headsets and like. All of the above mechanisms for interacting with our computer systems are worthwhile, but more importantly, they are all suited to specific ranges of engagement with our computers. That is, they afford certain kinds of actions (Dourish, 2001).

The other major way of interfacing with our computers is via the command line interface, or CLI. The CLI is also suited to specific ranges of engagement, and its the kind of engagement that often allows us greater control over our systems.

One reason the CLI provides greater control over our systems is because the interaction is all text-based. Text-based interaction requires more specificity than graphical-based interaction. By that I mean, it requires us to provide written instructions to a computer and to know what instructions to give it when we want the computer to perform some specific action. This means that we have to memorize some common instructions in order to use our systems. This is not necessarily difficult because many of the most common instructions, or commands, are mnemonic, but it does take some getting used to.

A second reason the CLI provides greater control over the system is that because it's text-based, it can be automated. We will not cover programming in this work or course, but know that all the commands that we will learn can be put in a text file, made into an executable file, and run like a program. This makes text-based interaction rather powerful.

Basic Commands

In light of that, I have developed two programs that will help you remember these basic commands. The commands that I'll ask you to learn encompass less than 0.3% of the commands that are available on a Linux system, but they are the most commonly used commands. Many of the other commands that are available are for very specific purposes. I'd estimate that despite having used the Linux command line for over 20 years, I've barely used 20% of them, and I might be stretching my estimate.

The first set of commands that I'll ask you to learn and practice include the following:

list files and directories.................. ls
print name of current/working directory..... pwd
create a new directory...................... mkdir
remove or delete an empty directory......... rmdir
change directory............................ cd
create an empty file........................ touch
print characters to output.................. echo
display contents of a text file............. cat
copy a file or directory.................... cp
move or rename a file or directory.......... mv
remove or delete a file or directory........ rm

You will practice these commands using the program that I wrote called learn-the-cli (I will show you how to install this and the other programs shortly).

I also developed a flashcards program that will help you learn an additional fifteen commands. This program is based on one created by someone else for a different purpose (see source code link above for credit). I'll explain these additional commands as we proceed through the semester. In the meantime, I'll ask that you periodically run the flashcards program to familiarize yourself with these commands, which includes the ones in the list above but also a few additional ones.

The Filesystem

In addition to the various commands that I'll ask you to learn, you will also have to learn the structure of the Linux filesystem. A filesystem has several meanings, but in this context, I refer to where the directories on the Linux system are placed. I find this to be the most difficult thing that new Linux users have to learn for a couple of reasons. First, modern operating systems tend to hide the filesystem from their users. So even though, for example, macOS is Unix, many macOS users that I have taught are completely unfamiliar with the layout of directories on their system. This is because, per my observations, macOS Finder does not show the filesytem by default these days. Instead it shows its users some common locations for folders. This might make macOS more usable to most users, but it makes learning the system more difficult.

What's common for both macOS and Linux operating systems is a filesytem based on a tree-like structure. These filesystems begin at what's called a root location. The root location is referenced by a forward slash: /. All directories branch off from root. The location to any directory is called a PATH. For example, our home directories on Linux will be located at the following PATH:

/home

That PATH begins at root / and ends at home.

It is a little different for Windows users. Since Windows is not Unix-like, it uses a different filesystem hierarchy. Many Windows users might be familiar with the basics, such as the C: drive for the main storage device or the D: drive for an added USB stick. As such, the Windows operating system uses multiple root directories (C:, D:, E:, etc.) I encourage you to read the following article on A quick introduction to the Linux filesystem for Windows users. The article is published by Red Hat, which makes its own Linux distribution.

In short, learning the Linux filesystem requires adopting a new mental model about how the operating system organizes its directories and files. Like learning the basic commands, it's not too hard, but it may take time and practice before it sticks. To help learn it, I wrote an additional program that will let you practice navigating around the Linux filesystem and making some changes to it. The program is called learn-the-filesystem. Before you use this program, I would like to encourage you to read another Red Hat article on Navigating your filesystem in the Linux terminal. It includes sections that my program will cover that include:

  • viewing file lists
  • opening a folder (aka, a directory)
  • closing a folder
  • navigating directories
  • absolute paths

Bash: The Bourne Again Shell

I should point out that the command line interface that we are using on our Linux servers is provided by a shell. A shell is "both an interactive command language and a scripting language" (see link above). We will use the shell strictly as a command language, but if you're interested someday, I'd encourage you to explore Bash as a scripting language (I personally script in Bash quite a lot). There are a variety of shells available for Linux and other Unix-like operating systems, but the most popular one and the one we will be using is called Bash.

Bash is an acronym for the Bourne Again Shell because it's based on the original Unix shell called the Bourne shell, written by Stephen Bourne. Bash itself was written by Brian Fox.

I think it's important to know the history of the technologies that we use, and Bash has a super interesting history that pre-exists Linux. Therefore, I highly encourage you listen to the Command Line Heroes episode titled Heroes in a Bash Shell, narrated by Saron Yitbarek. The episode recounts Brian Fox's history with the Bash shell while he worked for the Free Software Foundation in the 1980s.

Conclusion

We will spend the next few weeks practicing these commands and learning the filesystem. We'll do this because knowing these things is integral to accomplishing everything else in this work, including installing and setting up our content management systems and the integrated library system.

In the video for this week, I'll show you how to install the three programs that I wrote or modified. We will use git to download them. The we will move the programs to a specific directory in our executable PATH. This will allow us to run them simply by typing their names.

Installation

To install my practice programs, login to your Linux virtual instances, and run the following commands. You will learn more about these commands shortly.

First, let's take a look at the contents of your home directory (the default directory you're in when you connect to your virtual machine):

ls

Most likely, nothing will be listed.

Now let's retrieve the programs using the git command:

git clone https://github.com/cseanburns/learn-the-commandline.git

Run the ls command again, and you'll see a new directory called learn-the-commandline:

ls

Next, copy the programs to an executable path:

sudo cp learn-the-commandline/* /usr/local/bin

Run the first program and work through it in order to learn some of the basic commands:

learn-the-cli

When ready, run the second program in order to learn about the Linux filesystem:

learn-the-filesystem

Finally, periodically run the flashcards program to refresh your memory of the basic commands, plus some other commands that you'll learn about soon:

flashcards

References

Dourish, P. (2001). Where the Action Is: The Foundations of Embodied Interaction. MIT Press. https://doi.org/10.7551/mitpress/7221.001.0001