Getting Started

Command line

Up until now, you may have thought of the Finder (on macOS), or the File Explorer (on Windows), as the only way to access your files. The command line is an older, but still common, way to interact with the files on your computer. With the command line, you can browse, read, copy, move, edit, and do anything with your files just like with the Finder or File Explorer. The difference is, instead of having a graphical representation of your files and clicking around with your mouse, the command line is entirely text-based; meaning you only get to see and type words.

On macOS, the command line interpreter is the Terminal app. On Windows, it is the Command Prompt. “Command line”, “terminal”, and “command prompt” can be pretty much used interchangeably.

There are a few commands and tricks you will need to learn for navigating with the terminal. All commands are run by typing something then pressing return.

The ls command

In the terminal, you are always operating in a specific directory, or folder, that exists on your computer. To see a list of the files in the current directory, type ls then press return. For a more detailed list, try ls -alh.

The cd command

To change directories, type cd followed by the name of the directory you want to enter then press return. For example, cd Desktop. Note that the directory typed this way must be a subdirectory of the current directory (i.e., one of the directories that is listed by ls). If you want to go up a level, use cd ... You can go to a directory that is not a subdirectory of your current path, but you need to type the entire path; e.g., cd /Users/Tim/Desktop/Media.

I typically use the ls command every time after changing directories as a way of orienting myself.

Tab completion

Like all programming-related things, precision is important. If you mistype any part of a command, it won’t do what you want it to. Fortunately, the terminal has a feature that reduces mistypes. When you are typing some part of a command, you can try pressing tab and the terminal will try to expand it for you. This is most useful when used with cd. For example, if you type cd Des then press tab, the terminal will expand it to cd Desktop. Note that this may not work if there is more than one option for expanding (e.g., cd D can expand to cd Desktop or cd Documents because both begin with “D”), but you can always type a bit more and try tab again.

Command history

It can be tedious to type a new command every time, especially when it’s a command you used moments ago. The terminal keeps a history of the commands you’ve used and you can access it with the up and down arrow keys.

Example session on a Mac

Tims-Computer:~ tim$ ls
Applications Documents Library Music Public
Desktop Downloads Movies Pictures
Tims-Computer:~ tim$ cd Desktop
Tims-Computer:Desktop tim$ ls
Media
Tims-Computer:Desktop tim$ cd Media
Tims-Computer:Media tim$ ls
yt-video-01.mp4
Tims-Computer:Media tim$ cd ..
Tims-Computer:Desktop tim$ ls
Media
Tims-Computer:Desktop tim$ cd ..
Tims-Computer:~ tim$ ls
Applications Documents Library Music Public
Desktop Downloads Movies Pictures
Tims-Computer:~ tim$ cd /Users/tim/Desktop/Media
Tims-Computer:Media tim$ ls
yt-video-01.mp4
Tims-Computer:Media tim$ 

Editor

Using a featureful text editor is important for an enjoyable programming experience. My recommendation is Visual Studio Code (VS Code). Don’t worry, it’s completely free! VS Code is great because it’s more than just a text editor; it’s an integrated development environment (IDE), meaning its features go beyond editing text. It even has a built-in terminal, so you can do all your work solely within VS Code.

Other text editors popular among programmers include Emacs, Vim, Sublime Text, Atom, and Notepad++.

Node.js

Node.js is the industry standard JavaScript interpreter. You will need to download and install it to start programming with JavaScript in your terminal. After it is installed, open a new terminal window and run the command node -v. It should say the version of Node.js that you installed. If it doesn’t, make sure you open a new terminal window before running the command.

REPL

Node.js comes with a useful feature called a read-eval-print-loop (REPL). If you simply run the node command in your terminal, you will enter the REPL. This is an environment where every command you type will be interpreted as JavaScript. You cannot type regular command line commands in this mode.

Try entering the command 2 + 2 or console.log('Hello, world!'). To exit the REPL, press control+c twice.

C:\Users\Tim>node
Welcome to Node.js v12.16.1.
Type ".help" for more information.
> 2 + 2
4
> console.log('Hello, world!')
Hello, world!
undefined
>
(To exit, press ^C again or ^D or type .exit)
>

C:\Users\Tim>

Running a file

Much more useful than the REPL is the ability to have Node.js interpret an entire text file full of JavaScript code. To do this, you can type node followed by the name of the file you want to run. For example, node first.js will run a file called “first.js” that exists in the current directory.

As a brief walkthrough, go ahead and save a new text file with VS Code named “first.js” and write the following text in it.

console.log('Hello, world!');

In the terminal, navigate to the directory that contains “first.js” (using cd), then run the command node first.js. You should see Hello, world! appear in your terminal.

Tims-Computer:~ tim$ ls
Applications Documents Library Music Public
Desktop Downloads Movies Pictures
Tims-Computer:~ tim$ cd Documents
Tims-Computer:Documents tim$ ls
first.js
Tims-Computer:Documents tim$ node first.js
Hello, world!
Tims-Computer:Documents tim$