title: how to delete a file started with '-'
body: <p>How can I delete a file whose name started with '-'?</p>
  
  <p>For example, if I have a file named -a and I delete it with:</p>
  
  <pre><code>    rm -a
  </code></pre>
  
  <p>I will get:</p>
  
  <pre><code>    rm: invalid option -- 'a'
      Try 'rm --help' for more information.
  </code></pre>
  
  <p>So how can I do it?</p>