The Shell

What is a shell? Basically, it is the command line interface that power users (from this point forward, that includes you) control their computer's operating system with. Windows has a shell, Macs have a shell, and the Linux operating system has a shell.

Linux is the name of the operating system that you will be learning about for the rest of the course. For now, the only thing I want you to know is that one of the primary shells for it, named Bash, was written by Brian Fox, who is just a generally badass guy. His Wikipedia page is worth a read).

So to go back over what we just said, the shell runs in the operating system which runs on the computer. In this course we will be teaching you a ton about the terminal on the Linux operating system, and then a little bit about the underlying computer hardware.

Command Layout

So let's get into how the real hacker uses the command line, starting with a scene from The Matrix, an all-time great hacker movie.

That scene is actually pretty realistic, and a lot of the commands she runs are real things you will use throughout this course.

Let's get into the format of commands. First, there is either going to be a $ or a #. Going forward, I will use a $ to indicate the beginning of a command.

$

This indicates that you are in a shell of some format where you will be able to type a command.

$ command

When you run a command from the terminal, the shell is what will execute a program. These commands can do anything, from running a built-in program to the operating system, executing a script you wrote, the limit is what the command was programmed to do. We'll do a little programming in this course too!

$ command <argument>

We can also modify the program's behavior by adding what are called arguments. These arguments do things like configure settings, or tell programs to operate in a certain way to do something, and specify where to put output. To indicate an argument, we sometimes use something called a "flag" which says to the shell, hey, I am trying to modify the program that is running with the argument directly behind me. It looks something like this:

$ command -f <argument>

This command tells the shell to run the program "command" with the flag "-f" and the argument "argument". There can be dozens of flags and arguments to modify a command or how a program runs, so it gets complicated real quick. Luckily, there is a command named "man" we can use to find out what exactly those flags and arguments do to modify the command. We'll be best friends with "man" eventually, but for now, let's run our first commands!

Usually we would run a shell on a computer (like the Windows 'cmd line'), or maybe in something known as a virtual machine which you will set up later in this course, but we have an even cooler option these days due to what can basically be described as dark magic: Shell In the Browser! The Shell in the Browser I will have you use for this section is a small Linux operating system with most of the same functionality as a fully featured shell.

1. There is a shell embedded in this page right above this which should have finished loading by now. The same shell also lives here: https://www.hoppersroppers.org/shell/src/

Sometimes it takes a bit to load (~10 seconds), if it takes longer than 30 seconds, just press refresh. How it works and understanding what we are doing doesn't matter right now but by the end of the course, I guarantee you'll get it.

2. Once your in-browser Linux operating system has loaded, click into the terminal and enter your first command, 'whoami' and press enter.

It should return "root", which is the name on the Linux operating system for the most powerful user on the system! On your journey through hackerdom, you will learn to love "root" and all the power it gives you, but for now, let's run a few more commands to see what is going on.

3. Run the command 'echo "hello world" '. It will use the command 'echo' with the argument "hello world" to print to the screen. Hello world is the classic programming introduction demo, so congrats on officially making it!

3. Next, type the command 'ls' (like LS, but lowercase, then hit the Enter key) to list all the files in the directory.

4. Let's take that one step further now and add a flag to that 'ls' command with 'ls -l'. (the -l is a lowercase L, not an i!) The '-l' flag allows you to see the long information printout for the files listed.

5. Now let's make a file of our own! Run 'echo "hello world" > newfile.txt'. This command will use the echo command to output the words and then use the '>' to redirect the words into a file we named. You'll learn all about redirection and what we can do with that in this course, but for now, create the new file and run 'ls -l' again.

You should be able to see the new file and the updated time! (That time is off because the Linux operating system these commands are running in has their clock set to Coordinated Universal Time (UTC) but that is a completely different subject we'll ignore for right now)

6. There's a command named 'cat' on Linux which we can use to read files from the terminal. Use 'cat newfile.txt' to read the file you just created!

7. Run the command 'ls -al'. The "-a" flag makes it so you can see all files, and the "-l" flag allows you to see the long information printout for the files listed. Combined, they create this view.

Whoah! Now we can see a hidden file named ".ash_history". Linux hides files with a . in front of them from the normal "ls", but you can find them with "ls -a".

5. Let's use 'cat' to read the hidden file with 'cat .ash_history'.

Now we can see all the commands that we ran so far!!!

Congratulations! In this brief series of commands, we have figured out who we were, said hello to ourselves in a few ways, and found a hidden file. That's pretty awesome!

Honestly, you weren't supposed to understand everything (or anything) you did there, but I promise, by the end of this course all of those things will make sense.