Understanding the Terminal Window

When you first get access to a new computer or smartphone, you likely want to turn it on and get a feel for how to use it by checking which apps are available, and to learn where things are so that you can customize the device to suit your needs. You can become familiar with a computer through a terminal in a similar way.

The interactive terminal you launched in this browser window, by clicking the Launch an Interactive Terminal! button above, displays a white rectangle on the bottom of your browser window:

In many of these Unix (or *nix-based) operating systems, the symbols at the end of the prompt may be a $ symbol or a # symbol, which mean the following:

The user that is noted in the # environment is also known as a root user, which is considered to be a super user, or administrator, by default.

For our purposes within the browser terminal below, you are logged in as a regular user, but you also have administrator privileges via the sudo command. As this is a temporary terminal, you do not need to worry about what you type into the terminal, as we will destroy everything once we are done. Similarly, with a cloud server, it is possible to destroy a server and start fresh if something goes awry.

At this point, with your terminal launched in the browser, you can begin to type into it using your local computer. Your text will appear at the blinking cursor. We’ll learn about what we can type here in the next sections

Becoming Familiar with Directories

We’ll begin working with the terminal by typing a command. A command is an instruction that is given by a user, communicating what it is that the user wants the computer to do. You will be typing your commands into the terminal and then pressing ENTER or RETURN when you are ready for the computer to execute on a given command

Let’s type the following command followed by ENTER. You can also copy the command, or ask it to run in a launched interactive terminal by clicking on the relevant links in the code block below when you hover over it with a mouse.

Once you run this command, you’ll receive the following output:

The pwd command stands for “present working directory,” and it lets you know where you are within the current filesystem.

In this example, you are in the directory (or folder) called /home/sammy, which stands for the user called sammy. If you are logged in as root, a user with elevated privileges, then the directory would be called /root. On a personal computer, this directory may be called the name of the user who owns the computer. Sammy Shark’s computer may have /sammy or /sammy-shark or /home/sammy as their primary user directory.

Right now, this directory is empty. Let’s create a directory to store the files we’ll be creating as we go through this tutorial, which we can call files, for example.

To do this, we’ll use the mkdir command, which stands for “make directory.” After we type the command, we’ll need to write the name of the folder, which will pass the value to the command so that the command can execute on creating this directory. This value (the name of the folder) is known as an argument, which is an input being given to the command. If you are familiar with natural language grammar, you can think of the argument as an object that is being acted upon by the verb of the command.

In order to create a new directory called files we’ll write the following, with mkdir being the command and files being the argument:

After you run this command, you won’t receive any output other than a new line with a blinking cursor. With this fresh line on your terminal, you are ready for your next command.

Listing Contents and Understanding Permissions

As we have not received any concrete feedback about our new directory yet, we’ll use a command to learn more about what is in our present working directory. You can confirm that the new directory is indeed there by listing out the files in the directory, with the ls command (signifying “list”):

You’ll receive output that confirms the files directory is there:

This gives us general information about what is in our present working directory. If we want to have more details, we can run the ls command with what is called a flag. In Linux commands, a flag is written with a hyphen - and letters, passing additional options (and more arguments) to the command. In our example, we’ll add the -l flag, which — when paired with ls — denotes that we would like to use the option to use a long listing format with our command.

Let’s type this command and flag, like so:

Upon pressing ENTER, we’ll receive the following output in our terminal:

Here, there are two lines of output. The first line refers to computer memory blocks being allocated to this directory, the second line mostly refers to user permissions on the file.

To get a somewhat more human readable output, we can also pass the -h or --human-readable flag, which will print memory sizes in a human readable format, as below. Generally, one hyphen - refers to single-letter options, and two hyphens -- refer to options that are written out in words. Note that some options can use both formats. We can build multiple options into a command by chaining flags together, as in -lh.

For example, the two commands below deliver the same results even though they are written differently:

Both of these commands will return the following output, similar to the output above but with greater context of the memory blocks:

The first line of output lets us know that 4K of computer memory is dedicated to the folder. The second line of output has many more details, which we’ll go over in more detail. A general high-level reference of all the information that we’ll cover is indicated in the table below.

You’ll note that the name of our directory, files, is at the end of the second line of output. This name indicates which specific item in the /home/sammy user directory is being described by the line of output. If we had another file in the directory, we would have another line of output with details on that file.

At the front of the line, there is a list of characters and dashes. Let’s break down the meaning of each of the characters:

Navigating the Filesystem

So far, we have learned how to determine where we are in a filesystem, how to make a new directory, how to list out files, and how to determine permissions.

Let’s next learn how to move around the file system. We have made a new directory, but we are still in the main /home/sammy user directory. In order to move into the /home/sammy/files directory that we have created, we’ll use the cd command and pass the name of the directory we want to move into as the argument. The command cd stands for “change directory,” and we’ll construct it like so:

Again, you won’t receive output other than a new line with a blinking cursor, but we can check that we are in the /home/sammy/files directory with the pwd command we used earlier:

You’ll get the following output, confirming where you are:

Let’s move to the primary directory of the server. Regardless of where we are in a filesystem, we can always use the command cd / to move to the primary directory:

To confirm that we have moved and learn what is in this directory, let’s run our list command:

We’ll receive the following output:

Creating and Modifying Text Files

Let’s first be sure that we’re in the files/ directory of the /home/sammy user folder, which we can do by either verifying with pwd, or by changing directories on the absolute path:

We’ll begin by using the touch command, which can create a new file or modify an existing file. To use it, you can use the command touch and pass the name of the text file you want to create as the argument, as demonstrated below.

Once you press ENTER, you’ll receive a new line of the command prompt, and you can list the current contents of files/ to ensure it was created.

We can use echo directly on the command line to have the interface repeat after us. The traditional first program, "Hello, World!", can be written with echo like so:

Named for Echo of Ovid’s Metamorphosis, the echo command returns back what we request. In this case, it echoed, “Hello, World!” On its own, however, the echo command does not allow us to store the value of our text into a text file. In order to do that, we will need to type the following:

We can check that our new file exists, again with ls.

We now have two text files in our /home/sammy/files user folder. Next, we can confirm that the file sammy.txt does have the text we asked the terminal to echo into it. We can do that with the cat command. Short for concatenate, the cat command is very useful for working with files. Among its functions is showing the contents of a file.

Once we run the command, we’ll receive the following output:

If we were to run cat on the empty file ocean.txt, we would receive nothing in return as there is no text in that file. We can add text to this existing file with echo as well. Let’s add a quote from Zora Neale Hurston to the file.

Now, if we run cat on the file, we’ll receive output of the text we just entered.