php自定义函数如何记录log日志的案例

/**
 * 记录错误日志
 * @param 日志内容 $res
 */
function save_log($res) {
  $err_date = date("Ym", time());
  //$address = '/var/log/error';
  $address = './error';
  if (!is_dir($address)) {
    mkdir($address, 0700, true);
  }
  $address = $address.'/'.$err_date . '_error.log';
  $error_date = date("Y-m-d H:i:s", time());
  if(!empty($_SERVER['HTTP_REFERER'])) {
    $file = $_SERVER['HTTP_REFERER'];
  } else {
    $file = $_SERVER['REQUEST_URI'];
  }
  if(is_array($res)) {
    $res_real = "$error_date\t$file\n";
    error_log($res_real, 3, $address);
    $res = var_export($res,true);
    $res = $res."\n";
    error_log($res, 3, $address);
  } else {
    $res_real = "$error_date\t$file\t$res\n";
    error_log($res_real, 3, $address);
  }
}

$var =var_export(array('a','b',array('aa','bb','cc')),TRUE)

echo $var;