How to output when I use wp_handle_upload_prefilter, Wordpress
<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>