Add --gemfile option to bundle install

lib/bundler/cli.rb

@@ -46,11 +46,14 @@ def check
     method_option "without", :type => :array,   :banner => "Exclude gems that are part of the specified named group."
     method_option "relock",  :type => :boolean, :banner => "Unlock, install the gems, and relock."
     method_option "disable-shared-gems", :type => :boolean, :banner => "Do not use any shared gems, such as the system gem repository."
+    method_option "gemfile", :type => :string, :banner => "Use the specified gemfile instead of Gemfile"
     def install(path = nil)
       opts = options.dup
       opts[:without] ||= []
       opts[:without].map! { |g| g.to_sym }
 
+      # Can't use Bundler.settings for this because settings needs gemfile.dirname
+      ENV['BUNDLE_GEMFILE'] = opts[:gemfile] if opts[:gemfile]
       Bundler.settings[:path] = path if path
       Bundler.settings[:disable_shared_gems] = '1' if options["disable-shared-gems"]
       Bundler.settings.without = opts[:without]

spec/install/gems_spec.rb

@@ -276,6 +276,21 @@
     end
   end
 
+
+  describe "when passing in a Gemfile via --gemfile" do
+    it "finds the gemfile" do
+      gemfile bundled_app("NotGemfile"), <<-G
+        source "file://#{gem_repo1}"
+        gem 'rack'
+      G
+
+      bundle :install, :gemfile => bundled_app("NotGemfile")
+
+      ENV['BUNDLE_GEMFILE'] = "NotGemfile"
+      should_be_installed "rack 1.0.0"
+    end
+  end
+
   describe "disabling system gems" do
     before :each do
       build_gem "rack", "1.0.0", :to_system => true do |s|