gem executable that starts sinatra server not working

So I wrote a simple "Hello World" site using sinatra:

#!/usr/bin/env ruby

# sinatra_demo/bin/sinatra_demo

require 'rubygems'
require 'sinatra'

get "/hello" do
  "Hello World!"
end

And when I run it, it works, I can send my browser to http://localhost:4567/hello and get "Hello World":

% sinatra_demo/bin/sinatra_demo
== Sinatra/1.2.6 has taken the stage on 4567 for development with backup from WEBrick
[2011-06-30 09:29:58] INFO  WEBrick 1.3.1
[2011-06-30 09:29:58] INFO  ruby 1.9.2 (2011-02-18) [x86_64-darwin10.7.4]
[2011-06-30 09:29:58] INFO  WEBrick::HTTPServer#start: pid=73620 port=4567
127.0.0.1 - - [30/Jun/2011 09:30:10] "GET /hello HTTP/1.1" 200 12 0.0027
localhost - - [30/Jun/2011:09:30:10 EDT] "GET /hello HTTP/1.1" 200 12
- -> /hello
127.0.0.1 - - [30/Jun/2011 09:30:10] "GET /favicon.ico HTTP/1.1" 404 447 0.0004
localhost - - [30/Jun/2011:09:30:10 EDT] "GET /favicon.ico HTTP/1.1" 404 447
- -> /favicon.ico
127.0.0.1 - - [30/Jun/2011 09:30:10] "GET /favicon.ico HTTP/1.1" 404 447 0.0003
localhost - - [30/Jun/2011:09:30:10 EDT] "GET /favicon.ico HTTP/1.1" 404 447
- -> /favicon.ico
^C
== Sinatra has ended his set (crowd applauds)
[2011-06-30 09:30:12] INFO  going to shutdown ...
[2011-06-30 09:30:12] INFO  WEBrick::HTTPServer#start done.

However, when I try to package it as a gem:

#!/usr/bin/env gem build

# sinatra_demo/sinatra_demo.gemspec

require 'rubyg开发者_C百科ems'

Gem::Specification.new do |spec|
  spec.name = 'sinatra_demo'
  spec.summary = "A hello world webserver"
  spec.author = "rampion"
  spec.files = Dir['bin/*']
  spec.executables = ['sinatra_demo']
  spec.version = "1.0.0"
  spec.add_dependency('sinatra')
  spec.has_rdoc = false
end

I can install the gem fine:

% sinatra_demo/sinatra_demo.gemspec
WARNING:  no description specified
WARNING:  no email specified
WARNING:  no homepage specified
  Successfully built RubyGem
  Name: sinatra_demo
  Version: 1.0.0
  File: sinatra_demo-1.0.0.gem
% gem install sinatra_demo-1.0.0.gem
Successfully installed sinatra_demo-1.0.0
1 gem installed
Installing ri documentation for sinatra_demo-1.0.0...
Installing RDoc documentation for sinatra_demo-1.0.0...

But running the installed executable fails to start the webserver

% which sinatra_demo
~/.rvm/gems/ruby-1.9.2-p180/bin/sinatra_demo
% sinatra_demo
%

The gem's executable is getting run (from what I can tell via puts statements), but the webserver doesn't start.

What am I doing wrong? (gist for the files if you want to play with them)

---

You need to add

enable :run

to your application file, so that the built in web server will start.

From the Sinatra configuration settings:

By default, this setting is enabled only when the :app_file matches $0. i.e., when running a Sinatra app file directly with ruby myapp.rb.

When running the file directly this condition is true so the web server starts. When packaged as a gem however, the executable file that is actually run is really a wrapper script around your application file created by rubygems, so the condition is false and the web server doesn't start.

---

Just in case anyone else ends up here, there is also the possibility that app.rb is not in the folder you think it is.