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All right.
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So in this lesson I want to introduce you to directory creation,
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file creation and directory manipulation. And we're going to be doing all of this inside the command line,
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just with our keyboards.
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So again right now I'm starting in my root directory over here and I am going to create a new folder
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right here.
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So obviously I can go through the right click, New Folder, all of that, but we are pro developers now,
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so we're going to get used to using the command line. So the command is mkdir or make directory, and
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then we're going to give our directory a name,
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so let's just call it Angela, right?
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You can see, there you go, pops up a new folder called Angela.
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Now let's cd into this new directory, and you can see that if I click on here, or if I use ls,
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that there's absolutely nothing in there.
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It's a empty folder.
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So what if I wanted to create a file?
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So in our graphical user interface I could, say, open up an application, like TextEdit, and I could make
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a file and write something in it and then save it inside my new directory.
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So I would have to do a little bit of navigating in order to get there,
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and then I have to give my file a name, let's call it Text and hit save.
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So now we have to exit the application and after all of that work I've got a text file and if we do
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ls
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now, you can see that text.rtf exists. But if you want to do the same thing using the command line
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then it's as simple as simply typing touch to create a new file.
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Then we're going to specify the name of the file, let's call it Text2, and then we give it an extension,
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.txt. And you can open it either by double clicking on it, which is what we're used to, or you can
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simply write open Text2, and it will open it using the default application, which is TextEdit in a
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Mac. Now you can specify which application you want to open this file in, and all you have to do is say
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the open, and you're going to use a -a flag, then you're going to specify the application that you
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want to use.
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So let's say that we want to open it inside Atom. So I can write Atom, and then I can specify that the
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file that I want to open, so Text2.txt, and hit enter, and it will open up the Atom application
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that I've got and then open up my file for me to be able to edit.
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So what if you wanted to delete files inside the command line? So currently I'm inside the Angela folder
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and there are two files, and I want to delete my Text.rtf.
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So then all you need to do is just use the rm command, which removes files
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if you type the command as is, so just rm, and then we're going to specify Text.rtf to remove,
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and once I hit enter you'll see it disappear
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also in the Finder as well.
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Now what if I want to remove all the files inside a folder?
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So let's create some more text files. So let's call it Text.txt, and then let's create
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Text3.txt.
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So now I've got Text, Text2, Text3.
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Little bit of a tongue twister there.
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And I want to remove all of them.
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So to do that you have to be inside the directory that you want to remove all the files from, and if
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you want to know which directory you're currently in,
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you can either look at the part that's before your user name and prompt,
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so in this case I'm inside a folder called Angela on Angela's MacBook Pro, but you can also use the 
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pwd, or print working directory command, and then when you hit enter it tells you your entire path and
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your current folder location. And now I want to remove all of them in one go without having to type remove
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Text.txt, etc..
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So again we're using the remove command and then we're simply going to use the * as a wildcard
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which matches everything that has every single name.
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And now if I hit enter you can see that all my three files inside my current directory are removed.
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So do you remember in the beginning of this module we mentioned that using the command line gives you
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more power, more control?
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And, as we all know, with great power comes great responsibility, and that means that you have to be careful
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when using certain commands because the graphical user interface isn't there to protect you.
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So for example if you were not inside the directory that you wanted to delete, say if you were inside
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your root directory and you, you know, tried to remove all the files inside your root directory, then it's
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probably not such a great idea.
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So always check which location you're in before you're doing some of these destructive commands.
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Now if you're inside your root directory and you tried to do remove *,
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nothing bad is actually going to happen, because there aren't any files that are inside this directory.
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There's only folders and to remove folders or remove directories there's a different command.
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So now I want to remove this Angela folder that I've created and I'm inside the right place to do it.
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I'm inside my root directory which is at this level.
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And again always check where you are by using the ls command.
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You can see that I am at this level.
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So now I want to remove this Angela directory and if I just simply write remove Angela and I hit enter,
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you can see it says that Angela is a directory.
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So this remove command by itself is not going to work.
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So to do it we actually have to add a flag which is the -r flag.
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So this allows you to remove a directory.
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So now let's try that again remove -r, and then we're going to use the Angela directory, and if
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we watch over here and I hit enter you can see that that directory is now gone, including all the files
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that it held, all the folders that are inside the Angela folder, and it removes all of its child components.
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So again these are destructive commands.
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Be really careful when you're using them.
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And in fact there's a pretty hilarious bit of Internet history which is where somebody submitted a question
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to Stack Exchange Server Fault, which is similar to Stack Overflow,
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but it's more for sysadmin and network admins.
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So what he said was Monday morning mistake.
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He used the sudo command, which stands for super user do, which uses your admin privileges to basically
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allow you to do things are probably a little bit dangerous, and he used the remove command, and then the 
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-rf flag.
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So we've already seen the -r, which allows you to remove entire directories and all the folders
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and all the child folders it contains.
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He also used the f flag which stands for force,
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so this doesn't ask you for a confirmation.
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And then the very last thing which is something that you should probably never ever write and there's
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very few cases where this is actually useful which is the no-preserve-root.
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And what that means is that, along with everything else inside this command, it basically wipes your hard
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disk to the point where you cannot recover it.
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This guy said Monday morning mistake,
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I basically just wiped my entire server, which obviously contains data from other people who are using
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his server.
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And what do I do?
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So as it turns out this is actually a hoax where this guy is trying to advertise his server company.
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And I mean it's clever or is it not clever.
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I'm not sure that it's positive PR but it got a lot of attention on the internets.
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So if you're interested you can have a read of this, and I’ll link to it in this lesson,
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but basically if you have a look at the answers, you can see that this is something really bad to never
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do.
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So with great power comes great responsibility.
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And in this module I've introduced you to some of the most common commands that you're going to be finding
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yourself using and also some of the most common shortcuts.
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And if you want to learn more about the command line then this is a web site that I highly recommend.
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I have nothing to do with them, it’s just something that I found to be written quite well.
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So it's completely free,
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and it's called the Command Line Tutorial, Learn Enough Command Line to Be Dangerous.
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Again the title is repeating what we just said before, but it goes into more depth like grepping, curl,
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all of those things that you might have come across and you will certainly come across more of it in
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your journey as a developer.