title: Add date and time to pdf output file name
body: <p>I am exporting graph outputs from R to a pdf file.  </p>
  
  <p>I would like to add the <code>Sys.time()</code> and <code>Sys.Date(</code>) to the outfile name.</p>
  
  <p>For instance I have a statement</p>
  
  <pre><code>pdf("output filename.pdf", 8,10)
  </code></pre>
  
  <p>I would like to output to look like
  output <code>filename 2010-03-25 2pm.pdf</code></p>
  
  <p>or something similar.</p>