.gems version of rake gems:install.rb

namespace :gems do
  desc "Install missing gem dependencies"
  task :install do
    File.read("#{File.dirname(__FILE__)}/.gems").each do |gem_decl|
      gem_name, version, source = gem_decl[/^([^\s]+)/,1], gem_decl[/--version ([^\s]+)/,1], gem_decl[/--source ([^\s]+)/,1]
      begin
        version ? gem(gem_name, version) : gem(gem_name)
      rescue Gem::LoadError
        puts "Installing #{gem_name} #{version}..."
        cmd = "gem install #{gem_name}"
        cmd += " --version #{version}" if version
        cmd += " --source #{source}" if source
        puts `#{cmd}`
      end
    end
  end
end