PHP Symfony get absolute path from relative Path

gistfile1.aw

$relativePath = $this->config['foo'];
$pseudoPath = sfConfig::get('sf_root_dir') . DIRECTORY_SEPARATOR . $relativePath;
$absolutePath = realpath($pseudoPath);
if (!$absolutePath) {
  throw new Exception("File not found: $pseudoPath");
}
$this->use($absolutePath);