Bundler::DSL extension to provide OS-depended gems in Gemfile

dsl.rb

# lib/bundler/dsl.rb

# Bundler::DSL extension to provide OS-depended gems in Gemfile
# https://github.com/bundler/bundler/wiki/Platform-as-a-parameter
# 
# Allows to group os-dependent gems in blocks with one or more symbols, strings or regexps as parameters.
# OS name is obtained from `RbConfig::CONFIG['host_os']` or `RUBY_PLATFORM` if the first one is not available.
# 
# Place this file in the project's lib folder and require it in your Gemfile:
#   require File.expand_path('../lib/bundler/dsl', __FILE__)
module Bundler
  class Dsl
    # ==== Usage:
    #   os :linux do
    #     gem 'rb-inotify'
    #     gem 'libnotify'
    #   end
    # 
    #   # matching with multiple parameters
    #   os :linux, :darwin, :mac do
    #     gem 'unicorn'     
    #   end
    #   
    #   # Regexp
    #   os /mingw|mswin/ do
    #     gem 'wdm', "~> 0.1.0"
    #   end
    def os(*names)
      yield if os?(*names)
    end
    
    # You can also use if/unless:
    # ==== Usage:
    #   # single line, negative matching:
    #   gem 'unicorn' unless os? :mingw, :mswin
    def os_name_match?(*names)
      names.map! {|name| name.is_a?(Regexp) ? name : name.to_s }
      !!host_os[Regexp.union(*names)]
    end
    alias_method :os?, :os_name_match?
    
    def host_os
      @host_os ||= host_os_or_platform.downcase
    end
    
    private  
    def host_os_or_platform
      RbConfig::CONFIG['host_os'] 
    rescue => e
      return RUBY_PLATFORM
    end
  end
end

Example Gemfile:

require File.expand_path('../lib/bundler/dsl', __FILE__)
source 'https://rubygems.org'

gem 'rails', '3.2.14'
gem 'sqlite3'

# ... 

os :linux do
  gem 'rb-inotify'
  gem 'libnotify'
end

# matching with multiple parameters
os :linux, :darwin, :mac do
  gem 'unicorn'     
end

# Regexp
os /mingw|mswin/ do
  gem 'wdm', "~> 0.1.0"
end

# single line in group, negative matching:
group :production do
  gem 'unicorn' unless os? :mingw, :mswin
end