在Mac狮子中安装ruby1.9.3

osx-gcc-installer turns out to be a very good option to replace Xcode in order to install Ruby 1.9.3

These are the steps I have followed:

Download & install the latest version of osx-gcc-installer here (GCC-10.7-v2 is fine):https://github.com/kennethreitz/osx-gcc-installer/downloads

Install RVM as usual and select 1.9.3-head as the default ruby installation: https://rvm.io/rvm/install/
Install Homebrew: https://github.com/mxcl/homebrew/wiki/installation
Install libksba to resolve some dependencies with Ruby 1.9.3: brew install libksba

That's it! You should now have Ruby 1.9.3 installed on Mountain Lion working perfectly.

If you need some other packages, install them now through Homebrew, such as Imagemagick for example: brew install imagemagick

It's possible that you need XQuartz for Homebrew to work properly, as Apple is not shipping X11 since Mountain Lion. You can download it here: http://xquartz.macosforge.org/trac/wiki
EDIT:

Now (since 29th July) Command line tools for Xcode 4.4 are available.

So, the new steps are these:

Download & install Command line tools for Xcode 4.4 (you don't need to download Xcode):https://developer.apple.com/downloads/index.action

Install Homebrew: https://github.com/mxcl/homebrew/wiki/installation
Install automake: brew install automake

Install RVM as usual and select 1.9.3-head as the default ruby installation: https://rvm.io/rvm/install/
Optional step: You may need XQuartz for some components, for example for Imagemagick, so download & install XQuartz: http://xquartz.macosforge.org/trac/wiki