Starting on the `vagrant gem` command.

lib/vagrant.rb

@@ -136,6 +136,7 @@ I18n.load_path << File.expand_path("templates/locales/en.yml", Vagrant.source_ro
 # Register the built-in commands
 Vagrant.commands.register(:box)          { Vagrant::Command::Box }
 Vagrant.commands.register(:destroy)      { Vagrant::Command::Destroy }
+Vagrant.commands.register(:gem)          { Vagrant::Command::Gem }
 Vagrant.commands.register(:halt)         { Vagrant::Command::Halt }
 Vagrant.commands.register(:init)         { Vagrant::Command::Init }
 Vagrant.commands.register(:package)      { Vagrant::Command::Package }

lib/vagrant/command.rb

@@ -8,6 +8,7 @@ module Vagrant
     autoload :BoxRepackage, 'vagrant/command/box_repackage'
     autoload :BoxList,      'vagrant/command/box_list'
     autoload :Destroy,      'vagrant/command/destroy'
+    autoload :Gem,          'vagrant/command/gem'
     autoload :Halt,         'vagrant/command/halt'
     autoload :Init,         'vagrant/command/init'
     autoload :Package,      'vagrant/command/package'

lib/vagrant/command/gem.rb

@@ -0,0 +1,17 @@
+require "rubygems"
+require "rubygems/gem_runner"
+
+module Vagrant
+  module Command
+    class Gem < Base
+      def execute
+        # We just proxy the arguments onto a real RubyGems command
+        # but change `GEM_HOME` so that the gems are installed into
+        # our own private gem folder.
+        ENV["GEM_HOME"] = @env.gems_path.to_s
+        ::Gem.clear_paths
+        ::Gem::GemRunner.new.run(@argv.dup)
+      end
+    end
+  end
+end

lib/vagrant/environment.rb

@@ -11,7 +11,7 @@ module Vagrant
   # defined as basically a folder with a "Vagrantfile." This class allows
   # access to the VMs, CLI, etc. all in the scope of this environment.
   class Environment
-    HOME_SUBDIRS = ["tmp", "boxes"]
+    HOME_SUBDIRS = ["tmp", "boxes", "gems"]
     DEFAULT_VM = :default
     DEFAULT_HOME = "~/.vagrant.d"
 
@@ -34,6 +34,9 @@ module Vagrant
     # The directory where boxes are stored.
     attr_reader :boxes_path
 
+    # The path where the plugins are stored (gems)
+    attr_reader :gems_path
+
     # The path to the default private key
     attr_reader :default_private_key_path
 
@@ -80,6 +83,7 @@ module Vagrant
       setup_home_path
       @tmp_path = @home_path.join("tmp")
       @boxes_path = @home_path.join("boxes")
+      @gems_path  = @home_path.join("gems")
 
       # Setup the default private key
       @default_private_key_path = @home_path.join("insecure_private_key")