title: rbenv shell not command
body: <p>rbenv installed. but rbenv shell not command.</p>
  
  <pre><code>ationtekiMacBook-Air:~ dation$ rbenv versions
    system
  * 2.0.0-p247 (set by /Users/dation/.ruby-version)
  dationtekiMacBook-Air:~ dation$ rbenv version
  2.0.0-p247 (set by /Users/dation/.ruby-version)
  dationtekiMacBook-Air:~ dation$ rbenv shell
  rbenv: no such command `shell'
  </code></pre>
  
  <hr>
  
  <pre><code>ationtekiMacBook-Air:~ dation$ ruby -v
  ruby 1.8.7 (2012-02-08 patchlevel 358) [universal-darwin12.0]
  </code></pre>