Jag hittade min lösning och här är den:
Steg 1:Rensa upp din tidigare installerade rvm och Xcode
=> rm -rf ~/.rvm
=> sudo rm -rf /Developer
Steg 2:Installera Xcode från App Store eller så kan installationsprogrammet sparas i din Launchpad.
Steg 3:Installera HomeBrew:
=> mkdir -p /usr/local/Cellar
=> /usr/bin/ruby -e "$(curl -fsSL https://raw.github.com/gist/323731)"
Steg 4:Installera RVM
=> bash < <(curl -s https://rvm.beginrescueend.com/install/rvm)
=> echo '[[ -s "$HOME/.rvm/scripts/rvm" ]] && . "$HOME/.rvm/scripts/rvm" # Load RVM function' >> ~/.bash_profile
Steg 5:Installera Ruby 1.9.2
=> rvm install 1.9.2
=> rvm use ruby-1.9.2 --default
=> gem install rails thin bundler
=> rvm install 1.9.2-head
=> brew install git ack wget curl redis memcached libmemcached colordiff imagemagick
Steg 6:Installera MySql
=> brew install mysql
=> mysql_install_db --verbose --user=`whoami` --basedir="$(brew --prefix mysql)" --datadir=/usr/local/var/mysql --tmpdir=/tmp
=> mkdir -p ~/Library/LaunchAgents
=> cp /usr/local/Cellar/mysql/5.5.15/com.mysql.mysqld.plist ~/Library/LaunchAgents/
=> launchctl load -w ~/Library/LaunchAgents/com.mysql.mysqld.plist
=> mysql -u root
=> UPDATE mysql.user SET Password=PASSWORD('password') WHERE User='root';
=> FLUSH PRIVILEGES;