static File installOrUpdateYouTubeDL() {
  File file = youTubeDLExecutable();
  if (!file.exists()) ret forceInstallYouTubeDL();
  pcall {
    if (fileOlderThanNDays(file, 7))
      ret forceInstallYouTubeDL();
      
    // TODO: always -1
    /*long size = urlSizeByHEAD(youTubeDL_URL());
    print("youtube-dl size on server: " + size);
    if (size > 0 && size != fileSize(file))
      ret forceInstallYouTubeDL();*/
  }
  ret file;
}