mkmf.rb can't find header files for ruby on OS X 10.8.2

[flaccid]

It appears as though there are dependencies required contrary to the readme for OS X?

Using sudo gem install redcar:

Building native extensions.  This could take a while...
ERROR:  Error installing redcar:
    ERROR: Failed to build gem native extension.

/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/ruby.h


Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/ffi-1.8.1 for inspection.
Results logged to /Library/Ruby/Gems/1.8/gems/ffi-1.8.1/ext/ffi_c/gem_make.out

Perhaps it needs XCode and its Command Line Tools?
http://kevinpotgieter.wordpress.com/2012/12/06/ruby-gem-install-mkmf-rb-cant-find-header-files-for-ruby-problem/

[kattrali]

Yep, good catch! I suppose it was assumed to be installed, since you generally need Xcode and command line tools anyway to be working with Ruby on OS X. I'll update the readme.