title: How to output when I use wp_handle_upload_prefilter, Wordpress
body: <p>Simple request, how can I find what I got in $file ? (array ?)</p>
  
  <p>When I add print_r or echo, Wordpress only show me an error messeage.</p>
  
  <p>I googled, but I found nothing, because my poor english maybe.</p>
  
  <pre><code>function wp_modify_uploaded_file_names($file) {
      $info = pathinfo($file['name']);
      $ext  = empty($info['extension']) ? '' : '.' . $info['extension'];
      $name = basename($file['name'], $ext);
  
      $file['name'] = uniqid() . $ext; // uniqid method
  
      print_r($file);
  
     return $file;
  }
  
  add_filter('wp_handle_upload_prefilter', 'wp_modify_uploaded_file_names', 1, 1);
  </code></pre>