title: Ruby is unable to find a gem or "require" file
body: <p>A simple Ruby code</p>
  
  <pre><code>require 'rest-client'
  server = "http://localhost:3000"
  response = RestClient.get(server + "/posts.json")
  </code></pre>
  
  <p>It throws an exception </p>
  
  <pre><code>/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- rest-client (LoadError)
      from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
      from /home/alex/app1.rb:41:in `&lt;main&gt;'
  [Finished in 0.1s with exit code 1]
  </code></pre>
  
  <p><code>rest-client gem</code> is installed. And I'm using Ruby <code>1.9.3</code> and not <code>1.9.1.</code> Even more, there is no ruby <code>1.9.1</code> installed on my machine.</p>
  
  <pre><code>rvm rubies
  
     ruby-1.9.2-p290 [ x86_64 ]
     ruby-1.9.2-p320 [ x86_64 ]
  =* ruby-1.9.3-p194 [ x86_64 ]
  </code></pre>
  
  <p>What is that happening and do I get rid of that?</p>