Example for simple usage of Grape

app.rb

module POC
  class Example1 < Grape::API
    version 'v1'
    format :json

    desc 'root location'
    get '/' do
      error!({status: 400, message: 'Bad Request.'}, 400)
    end

    desc 'namespace for authentication purpose'
    namespace '/' do
      http_basic do |name, pass|
        {'admin' => 'admin'}[name] == pass
      end

      desc 'list all files located under current directory'
      get 'ls' do
        files = {}
        files[:files] = Dir[File.dirname(__FILE__) + '/**']
        files
      end
    end
  end
end

config.ru

#!/usr/bin/env ruby

require 'rubygems'
require 'bundler/setup'

Bundler.setup(:default)

require 'grape'
require 'json'
require File.dirname(__FILE__) + '/app.rb'

# you can execute it using: $ rackup config.ru
run POC::Example1

Gemfile

source "https://rubygems.org"

gem 'grape'
gem 'rack'