Separate bundle install foo and bundle install --disable-shared-gems.

lib/bundler.rb

@@ -114,8 +114,8 @@ def default_gemfile
     end
 
     def configure_gem_home_and_path
-      if path = settings[:path]
-        ENV['GEM_HOME'] = File.expand_path(path, root)
+      if settings[:disable_shared_gems]
+        ENV['GEM_HOME'] = File.expand_path(bundle_path, root)
         ENV['GEM_PATH'] = ''
       else
         gem_home, gem_path = Gem.dir, Gem.path

lib/bundler/cli.rb

@@ -44,16 +44,18 @@ def check
     end
 
     desc "install", "Install the current environment to the system"
-    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 "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."
     def install(path = nil)
-      remove_lockfiles if options[:relock]
-
       opts = options.dup
       opts[:without] ||= []
       opts[:without].map! { |g| g.to_sym }
 
       Bundler.settings[:path] = path if path
+      Bundler.settings[:disable_shared_gems] = '1' if options["disable-shared-gems"]
+
+      remove_lockfiles if options[:relock]
 
       Installer.install(Bundler.root, Bundler.definition, opts)
 

spec/install/gems_spec.rb

@@ -231,6 +231,46 @@
       bundled_app('vendor/gems/rack-1.0.0').should be_directory
       should_be_installed "rack 1.0.0"
     end
+
+    it "does not disable system gems when specifying a path to install to" do
+      build_gem "rack", "1.1.0", :to_system => true
+      bundle "install ./vendor"
+
+      bundled_app('vendor/gems/rack-1.1.0').should_not be_directory
+      should_be_installed "rack 1.1.0"
+    end
+  end
+
+  describe "disabling system gems" do
+    before :each do
+      build_gem "rack", "1.0.0", :to_system => true do |s|
+        s.write "lib/rack.rb", "puts 'FAIL'"
+      end
+    end
+
+    it "does not use available system gems" do
+      gemfile <<-G
+        source "file://#{gem_repo1}"
+        gem "rack"
+      G
+
+      bundle "install --disable-shared-gems"
+      should_be_installed "rack 1.0.0"
+    end
+
+    it "remembers to disable system gems after the first time" do
+      gemfile <<-G
+        source "file://#{gem_repo1}"
+        gem "rack"
+      G
+
+      bundle "install vendor/gems --disable-shared-gems"
+      FileUtils.rm_rf bundled_app('vendor/gems')
+      bundle "install"
+
+      bundled_app('vendor/gems/gems/rack-1.0.0').should be_directory
+      should_be_installed "rack 1.0.0"
+    end
   end
 
   describe "when packed and locked" do