VAGRANT_VAGRANTFILE env var to specify alternate filename for Vfile

CHANGELOG.md

@@ -38,6 +38,8 @@ FEATURES:
     VirtualBox provider config. [GH-1126]
   - `vagrant ssh` will execute an `ssh` binary on Windows if it is on
     your PATH. [GH-933]
+  - The environmental variable `VAGRANT_VAGRANTFILE` can be used to
+    specify an alternate Vagrantfile filename.
 
 IMPROVEMENTS / BUG FIXES:
 

lib/vagrant/environment.rb

@@ -81,11 +81,11 @@ module Vagrant
 
       # Set the Vagrantfile name up. We append "Vagrantfile" and "vagrantfile" so that
       # those continue to work as well, but anything custom will take precedence.
-      opts[:vagrantfile_name] ||= []
+      opts[:vagrantfile_name] ||= ENV["VAGRANT_VAGRANTFILE"] if \
+        ENV.has_key?("VAGRANT_VAGRANTFILE")
+      opts[:vagrantfile_name] ||= ["Vagrantfile", "vagrantfile"]
       opts[:vagrantfile_name] = [opts[:vagrantfile_name]] if \
         !opts[:vagrantfile_name].is_a?(Array)
-      opts[:vagrantfile_name] = ["Vagrantfile", "vagrantfile"] if \
-        opts[:vagrantfile_name].empty?
 
       # Set instance variables for all the configuration parameters.
       @cwd              = opts[:cwd]

test/unit/vagrant/environment_test.rb

@@ -284,6 +284,21 @@ VF
       env.config_global.ssh.port.should == 200
     end
 
+    it "should load from a custom Vagrantfile specified by env var" do
+      environment = isolated_environment do |env|
+        env.file("some_other_name", <<-VF)
+Vagrant.configure("2") do |config|
+  config.ssh.port = 400
+end
+VF
+      end
+
+      env = with_temp_env("VAGRANT_VAGRANTFILE" => "some_other_name") do
+        environment.create_vagrant_env
+      end
+
+      env.config_global.ssh.port.should == 400
+    end
   end
 
   describe "ui" do