I would like to know about alternative ways to build a development machine for Ruby 1.9.3 on OS X 10.8 Mountain Lion, that does not require Xcode.
Mountain Lion is now Golden Master as I'm writing this question, so it could be considered as final version. That cannot be said about Xcode, that is a preview release yet.
RVM recommends to install osx-gcc-installer over Xcode, but I would like not to mess my system.
What is the cleanest way to install Ruby 1.9.3 on Mountain Lion without Xcode?
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:
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:
brew install automake
Optional step: You may need XQuartz for some components, for example for Imagemagick, so download & install XQuartz: http://xquartz.macosforge.org/trac/wiki