Introduction to the command-line interface

Huh, it's exciting, right?! You'll write your first line of code in just a few minutes :)

Let us introduce you to your first new friend: the command line!

The following steps will show you how to use the black window all hackers use. It might look a bit scary at first but really it's just a prompt waiting for commands from you.

Please note that throughout this book we use the terms 'directory' and 'folder' interchangably but they are one and the same thing.

What is the command line?

The window, which is usually called the command line or command-line interface, is a text-based application for viewing, handling, and manipulating files on your computer. Much like Windows Explorer or Finder on Mac, but without the graphical interface. Other names for the command line are: cmd, CLI, prompt, console or terminal.

Open the command-line interface

To start some experiments we need to open our command-line interface first.

Windows

Go to Start menu → All Programs → Accessories → Command Prompt.

Mac OS X

Applications → Utilities → Terminal.

Linux

It's probably under Applications → Accessories → Terminal, but that may depend on your system. If it's not there, just Google it :)

Prompt

You now should see a white or black window that is waiting for your commands.

If you're on Mac or Linux, you probably see $, just like this:

$

On Windows, it's a > sign, like this:

>

Each command will be prepended by this sign and one space, but you don't have to type it. Your computer will do it for you :)

Just a small note: in your case there may be something like C:\Users\ola> or Olas-MacBook-Air:~ ola$ before the prompt sign and that's 100% correct.

The part up to and including the $ or the > is called the command line prompt, or prompt for short. It prompts you to input something there.

In the tutorial, when we want you to type in a command, we will include the $ or >, and occasionally more to the left. You can ignore the left part and just type in the command which starts after the prompt.

Your first command (YAY!)

Let's start with something simple. Type this command:

$ whoami

or

> whoami

And then hit enter. This is our result:

$ whoami
olasitarska

As you can see, the computer has just printed your username. Neat, huh?:)

Try to type each command, do not copy-paste. You'll remember more this way!

Basics

Each operating system has a slightly different set of commands for the command line, so make sure to follow instructions for your operating system. Let's try this, shall we?

Current directory

It'd be nice to know where are we now, right? Let's see. Type this command and hit enter:

$ pwd
/Users/olasitarska

If you're on Windows:

> cd
C:\Users\olasitarska

You'll probably see something similar on your machine. Once you open the command line you usually start at your user's home directory.

Note: 'pwd' stands for 'print working directory'.

List files and directories

So what's in it? It'd be cool to find out. Let's see:

$ ls
Applications
Desktop
Downloads
Music
...

Windows:

> dir
 Directory of C:\Users\olasitarska
05/08/2014 07:28 PM <DIR>      Applications
05/08/2014 07:28 PM <DIR>      Desktop
05/08/2014 07:28 PM <DIR>      Downloads
05/08/2014 07:28 PM <DIR>      Music
...

Change current directory

Now, let's go to our Desktop directory:

$ cd Desktop

Windows:

> cd Desktop

Check if it's really changed:

$ pwd
/Users/olasitarska/Desktop

Windows:

> cd
C:\Users\olasitarska\Desktop

Here it is!

PRO tip: if you type cd D and then hit tab on your keyboard, the command line will automatically autofill the rest of the name so you can navigate faster. If there is more than one folder starting with "D", hit the tab button twice to get a list of options.

Create directory

How about creating a practice directory on your desktop? You can do it this way:

$ mkdir practice

Windows:

> mkdir practice

This little command will create a folder with the name practice on your desktop. You can check if it's there just by looking on your Desktop or by running a ls or dir command! Try it :)

PRO tip: If you don't want to type the same commands over and over, try pressing the up arrow and down arrow on your keyboard to cycle through recently used commands.

Exercise!

Small challenge for you: in your newly created practice directory create a directory called test. Use cd and mkdir commands.

Solution:

$ cd practice
$ mkdir test
$ ls
test

Windows:

> cd practice
> mkdir test
> dir
05/08/2014 07:28 PM <DIR>      test

Congrats! :)

Clean up

We don't want to leave a mess, so let's remove everything we did until that point.

First, we need to get back to Desktop:

$ cd ..

Windows:

> cd ..

Using .. with the cd command will change your current directory to the parent directory (this is the directory that contains your current directory).

Check where you are:

$ pwd
/Users/olasitarska/Desktop

Windows:

> cd
C:\Users\olasitarska\Desktop

Now time to delete the practice directory:

Attention: Deleting files using del, rmdir or rm is irrecoverable, meaning deleted files will be gone forever! So, be very careful with this command.

$ rm -r practice

Windows:

> rmdir /S practice
practice, Are you sure <Y/N>? Y

Done! To be sure it's actually deleted, let's check it:

$ ls

Windows:

> dir

Exit

That's it for now! You can safely close the command line now. Let's do it the hacker way, alright?:)

$ exit

Windows:

> exit

Cool, huh?:)

Summary

Here is a summary of some useful commands:

These are just a very few of the commands you can run in your command line, but you're not going to use anything more than that today.

If you're curious, ss64.com contains a complete reference of commands for all operating systems.

Ready?

Let's dive into Python!