Getting started with Sinatra

Sep 16, 2015

Table of contents:

1. Installing Sinatra
2. Creating your first Sinatra application
3. Accepting URL parameters
4. Using Views
5. Conclusion

In the world of Ruby there are a number of web frameworks to choose from. Sinatra is a very popular “micro-framework” for building web applications.

This is perfect for building simple websites, applications or APIs that don’t require the weight or functionality of a framework like Ruby on Rails.

In today’s tutorial we will be looking at getting started with Sinatra to build a simple website.

Installing Sinatra

As we’ve seen over the last couple of weeks with Rake and Rack, like all good things Ruby, you can install Sinatra as a gem:

$ gem install sinatra

If you already have your Ruby environment set up correctly, this should just work and you will have Sinatra installed in just a few minutes.

Creating your first Sinatra application

Now that we have Sinatra installed we can go ahead and create our first Sinatra application.

Create a new file called app.rb with the following contents:

require 'sinatra'

get '/' do
  'Hello World!'
end

First we need to require sinatra into this application.

Next we define the "/" route, which will be the root of the application. This route will accept a GET request and return a body of "Hello World!".

Now if you run the following command in Terminal and then go to https://localhost:4567 in your browser you should see the correct response:

$ ruby app.rb

To define routes for other HTTP methods you can simply use the following syntax:

post 'posts' do
  # Create a new Post
end

put 'users/:id' do
  # Update the user
end

delete 'tags/:id' do
  # Delete the tag
end

Accepting URL parameters

An important part of any web application is accepting URL parameters. For example, you might want to have vanity URLs for your user’s profiles.

Sinatra makes it really easy to accept URL parameters and use them in your application:

require 'sinatra'

get '/:name' do
  "Hello #{params['name']}!"
end

Now if you go to https://localhost:4567/you_name you should be greeted by the application.

Using Views

If you are building an API with Sinatra, you might be able to get away with having everything in one file. However, if you are building a website, you will want to have view files for each page.

To use view files, create a new directory called views and then create a new file called index.erb:

<h1>Hello <%= @name %></h1>

Next, update your route definition to look like this:

get '/:name' do
  @name = params[:name]
  erb :index
end

In this example I’m simply grabbing the name from the params hash and then calling the index template.

Now if you restart the application and refresh your browser you should see the HTML from the index.erb view file.

Conclusion

This was only a brief introduction to Sinatra, but hopefully you can see how easy it makes building simple websites, applications or APIs.

It’s often the case that you need to provide a server backend for an application or service, but you don’t need the overhead of a fully blown web framework.

This is the perfect opportunity to use a micro-framework like Sinatra!