title: How to update tar (NOT append)
body: <p>I want to update an existing tar file with <strong><em>newer</em></strong> files.</p>
  
  <p>At GNU, I read:</p>
  
  <blockquote>
    <p>4.2.3 Updating an Archive</p>
    
    <p>In the previous section, you learned how to use ‘--append’ to add a
    file to an existing archive. A related operation is ‘--update’ (‘-u’).
    <strong>The ‘--update’ operation updates a tar archive by comparing the date
    of the specified archive members against the date of the file with the
    same name. If the file has been modified more recently than the
    archive member, then the newer version of the file is added to the
    archive (as with ‘--append’)</strong>.</p>
  </blockquote>
  
  <p>However,
  When I run my tar update command, the files are appended even though their modification dates are exactly the same. I want to ONLY append where modification dates of files to be tarred are newer than those already in the tar...</p>
  
  <pre><code>tar -uf ./tarfile.tar /localdirectory/ &gt;/dev/null 2&gt;&amp;1
  </code></pre>
  
  <p>Currently, every time I update, the tar doubles in size...</p>