title: Can't sudo gem uninstall (you don't have write permissions)
body: <p>I'm having trouble removing a gem from my system. When i ask gem where RedCloth is installed it says this:</p>
  
  <pre><code>    pteng01:trunk mike$ gem list -d RedCloth
  
      *** LOCAL GEMS ***
  
      RedCloth (3.0.4)
          Author: why the lucky stiff
          Rubyforge: http://rubyforge.org/projects/redcloth
          Homepage: http://www.whytheluckystiff.net/ruby/redcloth/
          Installed at: /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8
  
          RedCloth is a module for using Textile and Markdown in Ruby. Textile
          and Markdown are text formats.  A very simple text format. Another
          stab at making readable text that can be converted to HTML.
      pteng01:trunk mike$ 
  </code></pre>
  
  <p>I tried  </p>
  
  <pre><code>sudo gem uninstall --install-dir /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8
  </code></pre>
  
  <p>and i get this error</p>
  
  <pre><code>ERROR:  While executing gem ... (Gem::FilePermissionError)
  You don't have write permissions into the /usr/lib/ruby/gems/1.8/bin directory.
  </code></pre>