Joshua Vega, WB2JSV

Computer Science, NJIT 2019



Sinatra in 500 Words

04 November, 2016

Sinatra is a Domain-Specific Language (DSL) framework for writing web servers in Ruby. While not as complete and full as the popular Ruby on Rails framework, Sinatra still has enough built-in functionality to be extremely useful for anyone looking to develop a basic or even semi-complex web backend. In addition, the DSL-centered syntax makes Sinatra easy to read, write, and learn.

So without further ado, let’s learn some Sinatra.

NB: This tutorial assumes that you (the reader) have an basic understanding of an existing backend frameworks (such as Flask or ExpressJS). In addition, a basic knowledge of Ruby is useful.

But wait, before we move on, we need to install Sinatra. And in order to install Sinatra, we first need to install Ruby (if it isn’t installed already). To install Ruby, go to https://www.ruby-lang.org/ and follow the instructions to install Ruby for your operating system. Once installed, open a command-line window and run the following command (you may need to prefix the command with “sudo” if you are on a *nix operating system):

gem install sinatra

This will automatically download and install the latest version of Sinatra into the appropriate location(s) on your computer. If you don’t encounter any errors, you’re now free to continue.

The First Page

Let’s start by making a super-basic single page Sinatra server. Start by creating a folder that will hold all our Sinatra code for this tutorial. Once created, make a file named server.rb inside of it and open it up in a text editor. Put the following code in and save it:

require 'sinatra'

get '/' do
  erb :index
end

You can probably tell what this code snippet is doing, but just in case let’s do a quick rundown. The first line imports the Sinatra library, the third creates a route handler for the index route, and the fourth tells Sinatra to render the views/index.erb template. We were able to do all this with just four lines of code (and one empty line for readability) thanks to Sinatra’s amazing DSL.

Great, we’re just about halfway done with this tutorial. Next up we need to create that views/index.erb template Sinatra is expect. In order to do this, first create a directory in our project folder called views. Inside that newly created folder, create a file called index.erb and open it in a text editor. Put the following code in and save it:

<!DOCTYPE html>
<html>
<head>
  <title>Hello World</title>
</head>
<body>
  <h1>Hello World</h1>
</body>
</html>

And now comes the moment of truth. Open up a command-line window in the project folder and run the following command:

ruby server.rb

If all goes well, after a few seconds you should be able to navigate to http://localhost:4567/ in your web browser and see the simple “hello world” page from above.

Congratulations, you’ve officially written your first Sinatra server!

Conclusion

While the above sample isn’t all that impressive, we were able to write a fully-functioning web server in just 4 lines of Ruby code. This isn’t the extent of Sinatra’s abilities either, this is just the very tip of the iceberg. For its simplicity, Sinatra still has a surprising number of built-in features, making it ideal for both “quick and dirty” projects as well as more defined and planned projects.

So next time you’re thinking of writing a web server, consider Sinatra to get you up and running in no time.