WP_CLI::confirm PHP Method

    public static function confirm($question, $assoc_args = array())
    {
        if (!\WP_CLI\Utils\get_flag_value($assoc_args, 'yes')) {
            fwrite(STDOUT, $question . " [y/n] ");
            $answer = strtolower(trim(fgets(STDIN)));
            if ('y' != $answer) {
                exit;
            }
        }
    }

 /**
  * Regenerate thumbnail(s).
  *
  * ## OPTIONS
  *
  * [<attachment-id>...]
  * : One or more IDs of the attachments to regenerate.
  *
  * [--skip-delete]
  * : Skip deletion of the original thumbnails. If your thumbnails are linked from sources outside your control, it's likely best to leave them around. Defaults to false.
  *
  * [--only-missing]
  * : Only generate thumbnails for images missing image sizes.
  *
  * [--yes]
  * : Answer yes to the confirmation message.
  *
  * ## EXAMPLES
  *
  *     # re-generate all thumbnails, without confirmation
  *     wp media regenerate --yes
  *
  *     # re-generate all thumbnails that have IDs between 1000 and 2000
  *     seq 1000 2000 | xargs wp media regenerate
  */
 function regenerate($args, $assoc_args = array())
 {
     if (empty($args)) {
         WP_CLI::confirm('Do you really want to regenerate all images?', $assoc_args);
     }
     $skip_delete = \WP_CLI\Utils\get_flag_value($assoc_args, 'skip-delete');
     $only_missing = \WP_CLI\Utils\get_flag_value($assoc_args, 'only-missing');
     if ($only_missing) {
         $skip_delete = true;
     }
     $query_args = array('post_type' => 'attachment', 'post__in' => $args, 'post_mime_type' => 'image', 'post_status' => 'any', 'posts_per_page' => -1, 'fields' => 'ids');
     $images = new WP_Query($query_args);
     $count = $images->post_count;
     if (!$count) {
         WP_CLI::warning('No images found.');
         return;
     }
     WP_CLI::log(sprintf('Found %1$d %2$s to regenerate.', $count, _n('image', 'images', $count)));
     $errored = false;
     foreach ($images->posts as $id) {
         if (!$this->_process_regeneration($id, $skip_delete, $only_missing)) {
             $errored = true;
         }
     }
     if ($errored) {
         WP_CLI::log(_n('An error occurred with image regeneration.', 'An error occurred regenerating one or more images.', $count));
     } else {
         WP_CLI::success(sprintf('Finished regenerating %1$s.', _n('the image', 'all images', $count)));
     }
 }