wwtd chruby support

chruby.diff

diff --git a/lib/wwtd/ruby.rb b/lib/wwtd/ruby.rb
index ead4876..fb41fb3 100644
--- a/lib/wwtd/ruby.rb
+++ b/lib/wwtd/ruby.rb
@@ -6,6 +6,7 @@ module WWTD
       end
 
       # - rvm: "rvm xxx do"
+      # - chruby: "chruby-exec xxx --"
       # - others: env hash
       # - unknown: nil
       def switch_statement(version, options={})
@@ -22,6 +23,9 @@ module WWTD
             # don't print giant path hack :/
             "USE-RUBY-#{version}"
           end
+        elsif chruby_executable
+          command = "chruby-exec #{version} -- "
+          command if cache_command("#{command} ruby -v")
         else
           if ruby_root = ENV["RUBY_ROOT"] # chruby or RUBY_ROOT set
             switch_via_env(File.dirname(ruby_root), version)
@@ -54,6 +58,10 @@ module WWTD
         cache_command("which rbenv")
       end
 
+      def chruby_executable
+        cache_command("which chruby-exec")
+      end
+
       def cache_command(command)
         cache(command) do
           if result = capture(command)