A Beginner's Sinatra Tutorial

Posted by Joe Yates Wed, 07 Apr 2010 17:54:00 GMT

Using Sinatra reminds me of my first programming experiences - you write a tiny bit of code, with no overhead and get to see a result.

In the olden days your first program was probably in BASIC and was run from the command line, nowadays the equivalent is Web programming.

What follows owes a lot to the Sinatra README.

Installation

On Linux, you'll need Ruby and Rubygems installed (if not you should find installation instructions easily enough via a Web search).

Apart from Ruby, you'll need to use a text editor (e.g. GEdit) a Web browser and the Terminal (normally found in the Applications menu under Accessories).

Next install Sinatra:

$ gem install sinatra

1. Hello World!

Create a text file 'minimal.rb' and put the following in it:

require 'rubygems' if RUBY_VERSION < '1.9'
require 'sinatra';

get '/' do
  'Minimal Sinatra Hello World!'
end

Now, open a Terminal window and type:

ruby minimal.rb

Finally, go to this address: http://127.0.0.1:4567/

To stop the program, go to the Terminal window and press Ctrl+C

2. Structure: Sinatra::Base

It's useful to structure the program as a class.

Create a text file 'sinatra_base.rb' with:

require 'rubygems' if RUBY_VERSION < "1.9"
require 'sinatra/base'

class MyApp < Sinatra::Base
  get '/' do
    'Hello World!'
  end
end

MyApp.run!

Run it:

ruby sinatra_base.rb

3. Structure: A Separate App File

Create two files:

1. my_app.rb

require 'rubygems' if RUBY_VERSION < "1.9"
require 'sinatra/base'

class MyApp < Sinatra::Base
  get '/' do
    'Hello World from MyApp in separate file!'
  end
end

2. run_my_app.rb

require 'my_app'

MyApp.run!

Run it:

ruby run_my_app.rb

4. Rackup

Instead of writing a script to start the app, we can use Rackup to launch the same script:

Create a file 'config.ru':

require 'my_app'

run MyApp.new

Run it:

rackup config.ru

This time the application is visible at http://127.0.0.1:9292

If we want it to have the same address as before, we can run it like this:

rackup config.ru --port=4567

5. Static Files

A Web application will often have dynamic content (what we've created so far) and static content (e.g. images).

Create a directory 'static', and create a file called index.html in containing:

This is a static file.

my_app.rb:

require 'rubygems' if RUBY_VERSION < "1.9"
require 'sinatra/base'

class MyApp < Sinatra::Base
  set :static, true
  set :public, File.dirname(__FILE__) + '/static'
end

Now, if you run rackup, and go to http://127.0.0.1:4567/index.html you will see the content.

6. Routes

In the 'static' directory, create 'routes.html':

<ul>
  <li><a href="named_via_params/foo">Named parameters via params Hash</a></li>
  <li><a href="named_via_block_parameter/foo">Named parameters via block parameters</a></li>
  <li><a href="splat/foo/bar/baz">Multiple parameters via params[:splat]</a></li>
  <li><a href="splat_extension/myfile.txt">Filename via params[:splat]</a></li>
  <li><a href="regexp_params_captures/foobar">Using regular expression via params[:captures]</a></li>
  <li><a href="regexp_captures_via_block_parameter/foobar">Using regular expression via block parameters</a></li>
</ul>

And my_app.rb:

require 'rubygems' if RUBY_VERSION < "1.9"
require 'sinatra/base'

class MyApp < Sinatra::Base
  set :static, true
  set :public, File.dirname(__FILE__) + '/public'

  get '/named_via_params/:argument' do
    "
Using: '/named_via_params/:argument'<br/>
params[:argument] -> #{params[:argument]} (Try changing it)
"
  end

  get '/named_via_block_parameter/:argument' do |argument|
    "
Using: '/named_via_block_parameter/:argument'<br/>
argument -> #{argument}
"
  end

  get '/splat/*/bar/*' do
    "
Using: '/splat/*/bar/*'<br/>
params[:splat] -> #{params[:splat].join(', ')}
"
  end

  get '/splat_extension/*.*' do
    "
Using: '/splat_extension/*.*'<br/>
filename -> #{params[:splat][0]}<br/>
extension -> #{params[:splat][1]}
"
  end

  get %r{/regexp_params_captures/([\w]+)} do
    "params[:captures].first -> '#{params[:captures].first}'"
  end

  get %r{/regexp_captures_via_block_parameter/([\w]+)} do |c|
    "c -> '#{c}'"
  end

end

Go to http://127.0.0.1:4567/routes.html

You will see a list of links which exemplify different types of route matching.

7. Templates

Create a 'views' directory, and put a 'index.erb' file in it:

This is <%= @foo %>
Next, put the following in my_app.rb: 
require 'rubygems' if RUBY_VERSION < "1.9"
require 'sinatra/base'
require 'erb'

class MyApp < Sinatra::Base
  get '/template' do
    @foo = 'erb'
    erb :index
  end
end

You should get the following on http://localhost:4567/template:

Sinatra ERB Template