Sinatra

Sinatra is a DSL for quickly creating web applications in Ruby with minimal effort:

# myapp.rb
require 'sinatra'

get '/' do
  'Hello world!'
end

Install the gems needed:

gem install sinatra rackup puma

And run with:

ruby myapp.rb

View at: http://localhost:4567

The code you changed will not take effect until you restart the server. Please restart the server every time you change or use a code reloader like rerun or rack-unreloader.

Sinatra

Routes

In Sinatra, a route is an HTTP method paired with a URL-matching pattern. Each route is associated with a block:

get '/' do
  .. show something ..
end

post '/' do
  .. create something ..
end

put '/' do
  .. replace something ..
end

patch '/' do
  .. modify something ..
end

delete '/' do
  .. annihilate something ..
end

options '/' do
  .. appease something ..
end

link '/' do
  .. affiliate something ..
end

unlink '/' do
  .. separate something ..
end

Routes are matched in the order they are defined. The first route that matches the request is invoked.

Routes with trailing slashes are different from the ones without:

get '/foo' do
  # Does not match "GET /foo/"
end

Route patterns may include named parameters, accessible via the params hash:

get '/hello/:name' do
  # matches "GET /hello/foo" and "GET /hello/bar"
  # params['name'] is 'foo' or 'bar'
  "Hello #{params['name']}!"
end

You can also access named parameters via block parameters:

get '/hello/:name' do |n|
  # matches "GET /hello/foo" and "GET /hello/bar"
  # params['name'] is 'foo' or 'bar'
  # n stores params['name']
  "Hello #{n}!"
end

Route patterns may also include splat (or wildcard) parameters, accessible via the params['splat'] array:

get '/say/*/to/*' do
  # matches /say/hello/to/world
  params['splat'] # => ["hello", "world"]
end

get '/download/*.*' do
  # matches /download/path/to/file.xml
  params['splat'] # => ["path/to/file", "xml"]
end

Or with block parameters:

get '/download/*.*' do |path, ext|
  [path, ext] # => ["path/to/file", "xml"]
end

Route matching with Regular Expressions:

get /\/hello\/([\w]+)/ do
  "Hello, #{params['captures'].first}!"
end

Or with a block parameter:

get %r{/hello/([\w]+)} do |c|
  # Matches "GET /meta/hello/world", "GET /hello/world/1234" etc.
  "Hello, #{c}!"
end

Route patterns may have optional parameters:

get '/posts/:format?' do
  # matches "GET /posts/" and any extension "GET /posts/json", "GET /posts/xml" etc
end

Routes may also utilize query parameters:

get '/posts' do
  # matches "GET /posts?title=foo&author=bar"
  title = params['title']
  author = params['author']
  # uses title and author variables; query is optional to the /posts route
end

By the way, unless you disable the path traversal attack protection (see below), the request path might be modified before matching against your routes.

You may customize the Mustermann options used for a given route by passing in a :mustermann_opts hash:

get '\A/posts\z', :mustermann_opts => { :type => :regexp, :check_anchors => false } do
  # matches /posts exactly, with explicit anchoring
  "If you match an anchored pattern clap your hands!"
end

It looks like a condition, but it isn't one! These options will be merged into the global :mustermann_opts hash described below.

Conditions

Routes may include a variety of matching conditions, such as the user agent:

get '/foo', :agent => /Songbird (\d\.\d)[\d\/]*?/ do
  "You're using Songbird version #{params['agent'][0]}"
end

get '/foo' do
  # Matches non-songbird browsers
end

Other available conditions are host_name and provides:

get '/', :host_name => /^admin\./ do
  "Admin Area, Access denied!"
end

get '/', :provides => 'html' do
  haml :index
end

get '/', :provides => ['rss', 'atom', 'xml'] do
  builder :feed
end

provides searches the request's Accept header.

You can easily define your own conditions:

set(:probability) { |value| condition { rand <= value } }

get '/win_a_car', :probability => 0.1 do
  "You won!"
end

get '/win_a_car' do
  "Sorry, you lost."
end

For a condition that takes multiple values use a splat:

set(:auth) do |*roles|   # <- notice the splat here
  condition do
    unless logged_in? && roles.any? {|role| current_user.in_role? role }
      redirect "/login/", 303
    end
  end
end

get "/my/account/", :auth => [:user, :admin] do
  "Your Account Details"
end

get "/only/admin/", :auth => :admin do
  "Only admins are allowed here!"
end

Return Values

The return value of a route block determines at least the response body passed on to the HTTP client or at least the next middleware in the Rack stack. Most commonly, this is a string, as in the above examples. But other values are also accepted.

You can return an object that would either be a valid Rack response, Rack body object or HTTP status code:

An Array with three elements: [status (Integer), headers (Hash), response body (responds to #each)]
An Array with two elements: [status (Integer), response body (responds to #each)]
An object that responds to #each and passes nothing but strings to the given block
A Integer representing the status code

That way we can, for instance, easily implement a streaming example:

class Stream
  def each
    100.times { |i| yield "#{i}\n" }
  end
end

get('/') { Stream.new }

You can also use the stream hel

Sinatra

Install / Use

README

Sinatra

Table of Contents

Routes

Conditions

Return Values