Gem with dependencies

bin-foo

#!/usr/bin/env ruby
#this should be in bin/ dir - gist doesn't allow directories anymore

require 'haml'
puts Haml::VERSION

foo.gemspec

Gem::Specification.new do |s|
  s.name        = 'foo'
  s.version     = '0.1.0'
  s.summary     = "This is an example!"
  s.description = "Much longer explanation of the example!"
  s.authors     = ["Ruby Coder"]
  s.email       = 'rubycoder@example.com'
  s.files       = ["bin/foo"]
  s.homepage    = 'http://rubygems.org/gems/example'
  s.executables << 'foo'
  s.add_dependency('haml', '< 4.0')
end

output

gem-deps  (master %)$ gem list

*** LOCAL GEMS ***

bundler (1.2.3)
rake (10.0.3)
rvm (1.11.3.6)
gem-deps  (master %)$ gem install haml
Fetching: tilt-1.3.3.gem (100%)
Fetching: haml-4.0.0.gem (100%)

HEADS UP! Haml 4.0 has many improvements, but also has changes that may break
your application:

* Support for Ruby 1.8.6 dropped
* Support for Rails 2 dropped
* Sass filter now always outputs <style> tags
* Data attributes are now hyphenated, not underscored
* html2haml utility moved to the html2haml gem
* Textile and Maruku filters moved to the haml-contrib gem

For more info see:

http://rubydoc.info/github/haml/haml/file/CHANGELOG.md

Successfully installed tilt-1.3.3
Successfully installed haml-4.0.0
2 gems installed
gem-deps  (master %)$ gem build foo.gemspec 
  Successfully built RubyGem
  Name: foo
  Version: 0.1.0
  File: foo-0.1.0.gem
gem-deps  (master %)$ ./bin/foo 
4.0.0
gem-deps  (master %)$ gem install foo-0.1.0.gem 
Fetching: haml-3.1.8.gem (100%)
Successfully installed haml-3.1.8
Successfully installed foo-0.1.0
2 gems installed
gem-deps  (master %)$ foo
3.1.8 (Separated Sally)