title: list.files() all files in directory and subdirectories
body: <p>I'm trying to list all the files in a directories including subdirectories that end with <code>_input.txt</code>.</p>
  
  <pre><code>- folder 1
    - a_input.txt
    - folder 2
      - b_input.txt
  </code></pre>
  
  <p>If folder 1 were my working directory, I would like <code>list.files(pattern = "\\_input.txt$")</code> to be able to detect both <code>a_input.txt</code> and <code>b_input.txt</code></p>