diff --git a/rake/lib/git.rb b/rake/lib/git.rb
index 39b857e3..8ba57e75 100644
--- a/rake/lib/git.rb
+++ b/rake/lib/git.rb
@@ -1,7 +1,7 @@
 include Rake::DSL
 
 def git(url,dest)
-    sh "git clone #{url} #{dest}" unless File.exists?(dest)
+    sh "git clone #{url} #{dest}" unless Dir.exists?(dest)
 end
 
 def github(repo,dest)
diff --git a/rake/lib/homebrew.rb b/rake/lib/homebrew.rb
index 8122c3e8..79901697 100644
--- a/rake/lib/homebrew.rb
+++ b/rake/lib/homebrew.rb
@@ -38,26 +38,34 @@ module Homebrew
     end
 
     def self.has_keg?(keg)
-        system("#{BIN} search #{keg}")
+        `#{BIN} search #{keg}`
     end
 
     def self.is_keg_installed?(keg)
-        system("#{BIN} list | grep -w '#{keg}'")
+        `#{BIN} list | grep -w '#{keg}'`
     end
 
     def self.is_cask_installed?(cask)
-        system("#{BIN} cask list | grep -w '#{cask}'")
+        `#{BIN} cask list | grep -w '#{cask}'`
     end
 
     def self.is_tapped?(tap)
-        system("#{BIN} tap | grep -w '#{tap}'")
+        `#{BIN} tap | grep -w '#{tap}'`
     end
 
     def self.is_installed?
-        File.exists?("usr/local/bin/brew")
+        File.exists?("/usr/local/bin/brew")
     end
-    
-    def self.update()
-        sh "#{BIN} update && #{BIN} upgrade"
+
+    def self.prefix(keg)
+        `#{BIN} --prefix #{keg}`.strip
+    end
+
+    def self.update(*args)
+        if args.length > 0
+            sh "#{BIN} upgrade #{args.join(' ')}"
+        else
+            sh "#{BIN} update && #{BIN} upgrade"
+        end
     end
 end
diff --git a/rake/lib/output.rb b/rake/lib/output.rb
index f042f060..898c7e6e 100644
--- a/rake/lib/output.rb
+++ b/rake/lib/output.rb
@@ -3,3 +3,7 @@ require 'colorize'
 def echo(msg)
     puts "=> #{msg}".bold.green
 end
+
+def echoerr(msg)
+    puts "=> #{msg}".bold.red
+end