php正则表达式奇怪的错误

Question

i use such regex $msg = preg_replace('/<b>(\w)<\/b>/', '9999', $msg); to replace <b>test</b> but it not replace. why?

Answer 1

Notice the plus after \w+

 $msg = preg_replace('/<b>(\w+)<\/b>/', '9999', $msg);