installing cocoapods

gem update --system
gem install cocoapods

Gave this error.

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

http://docs.cocoapods.org/guides/installing_cocoapods.html says

"If you used an pre release version of Xcode you might need to update the command line tools."

I did not have commandline tools installed. So installed it  - and tried installing cocoapods - success :)

xcode command line tools