find_drupal_bootstrap.php

<?php 

$finder = new Finder();
    $dot_dot = '';
    while (true){
      try {
        $iterator = $finder
          ->files()
          ->name('bootstrap.inc')
          ->in(getcwd() . '/'. $dot_dot . 'core/includes/');
        break;
      } catch(\InvalidArgumentException $e) {
        $dot_dot .= '../';
        if (realpath(getcwd() . '/' . $dot_dot) == '/')
          throw new \InvalidArgumentException("Don't find Drupal base");
      }
    }

    foreach ($iterator as $file) {
      $bootstrap_real_path = $file->getRealpath();
    }

    $bootstrap_path = $input->getParameterOption(array('--bootstrap-file', '-b'))? : $bootstrap_real_path;