How can I remove this type p tag <p> </p> using DOM or regex?
I want to remove multiple p like this too,
<p> </p>
<p> </p>
<p> </p>
If you want to remove a string that is exactly, always, '<p> </p>', the simplest and fastest solution is probably to use str_replace() :
$new_string = str_replace('<p> </p>', '', $old_string);
I don't think it's necessary to use DOM for such a simple case -- and a regex is not necessary here.
Of course, if you need to replace something more complex, that is not always exactly the same string... well, it'll be time for DOM manipulations ;-)