ruby on rails - Rubygems do not install on OS X Lion

Question

I used to have no problems at all with ruby, gems and all related stuff. But after installing X Code Developer Tools and upgrading to Lion the gems do not install.

I get the following error for every gem. This is the message for sqlite as an example:

Building native extensions.  This could take a while...
ERROR:  Error installing sqlite3:
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/sqlite3-1.3.4 for inspection.
Results logged to /Library/Ruby/Gems/1.8/gems/sqlite3-1.3.4/ext/sqlite3/gem_make.out

What went wrong? How to fix it?

Answer 1

I had to install the Command Line Tools in the latest Xcode-Version (4.3.1) and

sudo gem install rails

worked like a charm.

To install Command Line Tools, go to Xcode Preferences > Downloads or use the following command in terminal (thx @Purell):

xcode-select --install