Ellane learns the command line

File paths

You stumbled in to a meme! What are the odds.

We'll come back to vim, which it turns out you can also launch by typing view (I had no idea!), much later.

But for now, yes, that's a valuable lesson. There are many situations where guessing a thing is a good idea. The CLI is not one of them.

(I might ask you to guess things, like cd Documents, where I'm pretty sure you're not going to accidentally wipe your hard drive.)

cd'ing to a nested folder #

File paths are core to this whole experience: many things you do involve a file, or being in a specific folder before you take an action. So let's go a bit deeper.

We'll need a subfolder, which it sounds like you have. But to keep this example simple I'm going to get you to create one on your Desktop; then people following along at home can use the same commands.

So, using the Mac Finder, create a folder called TestFolder on your Desktop. Note the lack of a space between the words.

The / forward slash #

This is the long way around:

cd `# takes you home if you're not already there`
cd Desktop
cd TestFolder

That # takes you home... bit in grey is a comment. Don't type that bit, including the first backtick. I'll use these to add comments to specific lines, or to show you what output to expect.

Or you can do it in a single step by using the / forward-slash, which separates subfolders.

cd
cd Desktop/TestFolder

Your prompt should update, and pwd will show you where you are.

Specify 'my home folder' #

We know that Desktop is in our home folder. But we might not be there already, so we have that annoying first cd to take us there.

We can skip this by using the shortcut for my home folder which is ~.

cd ~/Desktop/TestFolder

This is a common shortcut that you'll see in online instructions. It's handy because the person writing doesn't need to know where your home folder is: ~ is universal. Keep an eye out for it.

. and .. also have special meaning #

A single . in a file path means the folder that I'm currently in.

So this works. It's not useful here, but later we'll see where we do use this.

cd ~/Desktop
cd ./TestFolder
pwd `# /Users/ellane/Desktop/TestFolder`

Two periods .. means the parent folder. You use this one all the time.

cd ~/Desktop/TestFolder
cd ..
pwd `# /Users/ellane/Desktop`

This works everywhere #

You can use all of these wherever you'd type a file path; it's not just a cd thing.

So you can ls ~/Downloads/some/other/folder.

You can combine all of this #

This crazy thing works. You'd never do it, but it works.

ls ~/../john/Desktop/TestFolder/../../././Downloads
`# lists the chaos of my Downloads folder`

Note that my username is john. Substitute for yours: if you're not sure what it is, whoami 🟢 will show it. In these lessons I assume it's ellane.

Make sure you understand why this works. Make some of your own crazy file paths just for practice.

Relative vs. absolute paths #

File paths can be relative or they can be absolute.

If they're relative, they're relative to where you are. This is what we've seen so far.

cd
cd Desktop `# relative to your current location`

These are usually shorter and more convenient. But they can go wrong: someone might assume you're in folder A, and tell you to issue some instruction that includes a relative file path.

But if you're actually in folder B, the results are unpredictable.

So we can specify absolute file paths that work regardless of where you are. We've already seen one.

cd ~/Desktop
pwd `# /Users/ellane/Desktop`

pwd always reports an absolute file path.

/Users/ellane/Desktop #

Let's look at this in detail.

The first thing to note is that it starts with a forward-slash. This is another special character: at the beginning of a file path, it means the top of my file system.

Try this.

ls /

Seem familiar? Before you move on, see if you can find this same location in a Finder window.

You're looking at a listing of what we call the root of your file system.

In Finder, it's what you see if you open the Macintosh HD view.[1] Or from your home folder, you can Command-up arrow twice.

In Finder, Command-up arrow takes you up to the parent folder. So if you compare this view to /Users/ellane -- the absolute path to your home folder -- it should make sense.

  1. The first Command-up arrow is like typing cd .., and takes you to /Users.
  2. The second does the same again, and takes you to /. The root of your file system.

Absolute paths basically always start with a /. I'm sure there's an exception, but if you have that in mind, you won't go far wrong.

That slash says, regardless of where you are, go back to the top. It's very powerful.

Keep playing #

Of course all of this is interlinked.

cd /Users/./ellane/../ellane/Desktop/TestFolder/..

Again, absurd, but you get the idea.

The shared user #

Note that there's another user on your Mac whose home folder is at /Users/Shared if you want to play around with more paths.

This is an exact science #

Pay attention to how you see file paths written online. You will never, ever see someone specify Users/Shared. Because that's a relative path.

If your current directory just happens to be / then that's valid. But it probably isn't. So it'll always be specified as /Users/Shared.

Get super comfortable with this #

Simple enough concepts but you need to know these backwards. Just have a good play around and let me know if you find anything interesting.

  1. Assuming you haven't renamed your drive. ↩︎