function limit_text($text, $limit) {
      if (str_word_count($text, 0) > $limit) {
          $words = str_word_count($text, 2);
          $pos = array_keys($words);
          $text = substr($text, 0, $pos[$limit]) . '...';
      }
      return $text;
    }

echo limit_text('Hello here is a long sentence blah blah blah blah blah hahahaha haha haaaaaa', 5);

输出：

Hello here is a long ...