title: rvm install rails on Mac OSX 10.7.3
body: <p>was hoping someone could point me in the right direction as I am unable to find a previously posted answer to my question of trying to install rails on my mac mini running Lion OSX 10.7.3. I have ruby version 1.8.7 and rvm 1.12.5 but when I come to install rails using sudo gem install rails I get the following:</p>
  
  <pre><code>Building native extensions.  This could take a while...
  ERROR:  Error installing rails:
      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/json-1.7.0 for inspection.
  Results logged to /Library/Ruby/Gems/1.8/gems/json-1.7.0/ext/json/ext/parser/gem_make.out
  </code></pre>
  
  <p>The content of gem_make.out are:</p>
  
  <pre><code>/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
  </code></pre>
  
  <p>which did not really help me so not sure what it is I am missing? Any help or directions to help me solve this problem would be appreciated. Many thanks.</p>