Ellane learns the command line

The structure of a command

Feedback on homework #

Regarding closing the window vs. typing logout, not only does it feel like getting out before putting the car in 'park', it feels like opening the door and jumping out while the car is moving!

Now, this isn't what actually happens. When you close the Terminal window, it sends a signal to the CLI, and if something important is happening you'll be warned about it. It's like how modern cars lock the doors when you start moving: it makes it difficult (but not impossible) to jump out as you're hurtling down the motorway.

I think Gordon hit the spirit of it. When you're in the CLI, that's where your control is; that's where you should be issuing commands.

This is a Windows (as in Microsoft) vs. Unix mindset. Windows people think in the GUI. Unix people think in the CLI. When you're doing this stuff, put your CLI hat on.

We'll come back to this passing-around-of-signals in the future.

Tech support question #

For those of you following along at home, Ellane's Terminal window is responsive again. I tooted her a video of 'normal behaviour', which is exactly what you'd expect: after each command, you can type the next command.

We're not sure what was going on there, so we'll keep an eye on it.

The structure of a command #

Let's get to the good stuff.

Commands are all structured in the same way. They all follow one of a few patterns. When you learn those patterns, you learn the syntax of all commands.

We know that pie lunch cook isn't a valid sentence, even if we're not a chef.

And soon you'll immediately recognise that --food pie &meal lunch cook couldn't ever be a valid command: it just doesn't look right.

cook --meal lunch pie, however: while that isn't a valid command, it could be.

The first thing is always the command #

The command is the thing that decides what happens. Are you moving, copying, deleting, listing, installing, or printing a thing? It doesn't matter: but it comes first.

And sometimes that's all there is. We've already seen this: printenv. That was it. That was the command.

Let's introduce a few that we'll actually use.

Command traffic lights 🚦 #

When I introduce a new command, I'll always give it a traffic light:

Reference page #

I'll also create a short entry for each command on the new reference page.

These will be brief, as every command has its own documentation. We'll see that later.

New command: cd 🟢 #

Many -- most? -- commands are abbreviations of the thing that they do.

The shorter the command, the older it likely is. cd stands for change directory and it's older than me.

You can use it with no arguments. I'll introduce and define these soon. But for now, just type it.

cd

You should be underwhelmed! Nothing happened? But actually something did.

For one, you didn't get an error. Try garbage -- lksjdfl -- and see what happens.

Always pay attention to the output of a command. Never just assume that it worked. If it didn't work, it'll always tell you.

New command: ls 🟢 #

Try this one.

ls

This is short for list directory contents. And look at the results: seem familiar?

Pause here until you know exactly what you're looking at.

Guess this next bit #

So we're looking at the contents of your home folder. That's where a Terminal window opens to, by default.

Let's change directory. Try to guess how to move in to your Documents folder. Type it in.

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cd Documents

Again, it doesn't look like much happened. But notice two things: first, your prompt has changed. It now has the word Documents before the %.

Second, if you try ls again, you'll see the contents of your Documents folder.

Change directory. List the contents. Change directory. List the contents.

This is something you do all the time.

Arguments #

You just saw your first argument: Documents was an argument to the cd command.

We'll go in to this in detail later, I just wanted to briefly note it here.

New command: pwd 🟢 #

This one stands for print working directory. Try it and see what you get.

You cd'd to your Documents folder, so it should say something like

/Users/ellane/Documents

So you know where you are because your prompt gives you a clue, and if you want to be totally certain, you pwd.

This syntax, with the forward slashes, is very specific. I'll explain it soon.

How to get home #

changing directory to your home folder is such a common task, there's a shortcut for it.

We've already seen it. Care to guess?

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cd

cd with no arguments takes you home.

Take yourself on a trip 🚗 #

Use these commands a bunch until you're really comfortable with them. See where you can go. And see where you can't go.

You might have some questions about how you move around. Let me know. If not, we'll keep going.