file_get_contents()エラー判定

gistfile1.php

<?php

$context = stream_context_create(array(
  'http' => array(
    'ignore_errors' => true,
    'header' => 'User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)',
  )
));
$response = file_get_contents($url, false, $context);

$pos = strpos($http_response_header[0], '200');
if ($pos === false) {
  echo 'error';
}