正则表达式30分钟入门教程(一篇不错的学习教程)

Which introduced this error:

/usr/bin/gem:23: uninitialized constant Gem::GemRunner(NameError)

Simply add the line to the file /usr/bin/gem (may be different on a mac)

require 'rubygems/gem_runner'

after

require 'rubygems'

This fixed the issue in both Ubuntu and OS 10.4.