undefined method `run' for main:Object (NoMethodError) Sinatra - sinatra

Question

require 'sinatra/base'
class Foo < Sinatra::Base
get('/foo') { 'foo' }
end
class Bar < Sinatra::Base
get('/bar') { 'bar' }
end
run Rack::Cascade, [Foo, Bar]
I just can't guess what is wrong with this code.
When I ran: ruby server.rb, it throws an error

Answer 1

First of all, the last line should read
run Rack::Cascade.new [Foo, Bar]
But you can only use this in a Rackup File. So second, you need to create a File called config.ru (Rackup File) with the following contents:
require './app'
run Rack::Cascade.new [Foo, Bar]
and a file called app.rb with your actual app:
require 'sinatra/base'
class Foo < Sinatra::Base
get('/foo') { 'foo' }
end
class Bar < Sinatra::Base
get('/bar') { 'bar' }
end
then you can start the server by typing in the command line
$ rackup
>> Thin web server (v1.3.1 codename Triple Espresso)
>> Maximum connections set to 1024
>> Listening on 0.0.0.0:9292, CTRL+C to stop
after that, open a second command line window and test your app:
$ curl 0.0.0.0:9292/foo
foo%
$ curl 0.0.0.0:9292/bar
bar%