title: List files with specific word and file extension
body: <p>I have a bunch of files in a directory that contain various extensions, but the ones I'm most interested in are *.bil.  For each year there are 12 files.
  What I'm stuck on is matching a year with *.bio, so my list will have 12 files for year 2000.
  Example filenames:</p>
  
  <p>**** Edit (added actual filenames):</p>
  
  <pre><code>PRISM_tmin_stable_4kmM2_200001_bil.bil
  PRISM_tmin_stable_4kmM2_200002_bil.bil
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>Filenames &lt;- list.files("/../directory", pattern = "//.bil")
  </code></pre>
  
  <p>This will select all*.bil files but there are hundreds, so I need to specify only year 2000.</p>
  
  <p>Any ideas?</p>