qichunren@zhaobak:~> gem install hpricot
ERROR: While executing gem ... (Gem::FilePermissionError)
You don't have write permissions into the /opt/ruby-enterprise-1.8.7/lib/ruby/gems/1.8 directory.
For a systemwide Ruby install, become root. For example:
$ sudo gem install hpricot
However, the modern approach in many circumstances, including in development, is to use a tool that lets you easily install and use Ruby as a normal user. This lets you avoid having to become root. There are a few such tools, and the one I use is RVM.
# install rvm into your ~ $ \curl -sSL https://get.rvm.io | bash -s stable # install latest version of ruby into your ~ $ rvm install ruby # installs a gem into your ~ $ gem install $SOME_GEM_NAME