正则表达式删除div

I have a file like:

<div clas='dsfdsf'> this is first div </div>
<div clas='dsfdsf'> this is second div </div>
<div class="remove"> 
  <table> 
  <thead> 
   <tr> 
     <th colspan="2">Mehr zum Thema</th> 
  </tr> 
</thead> 
<tbody>
  <tr> this is tr</tr>
  <tr> this row no 2 </tr>
</tbody>
</table>
</div>
 <div clas='sasas'> this is last div </div>

I have get this file content in a variable like this:

$Cont = file_get_contents('myfile');

Now I want to replace div with class name 'remove' by preg_replace. I have tried this:

$patterns = "%<div class='remove'>(.+?)</div>%";  
$strPageSource = preg_replace($patterns, '', $Cont);

It did not work. What should be the correct regular expression for this replace?

Try this code.

preg_replace("/<div class='remove'>(.*?)<\/div >/i", "<div class="newClass">Newthings</div> ", $Cont);

As it has been stated in the comments, you should not be using regex to parse HTML. Because there's no sane way for you to extract that <div> if there're other nested <div>'s inside. I.e.

<div clas='dsfdsf'> this is second div </div>
<div class="remove"> 
      some text <div>nested div</div> more text and some elements<br />
</div>

What you want to do is find the location of your <div class="remove"> and then advance through the HTML (parse it) in the following manner

1) set $nesting_counter = 0
2) proceed through HTML until you encounter either <div> or </div>
    a) if found <div>
           $nesting_counter++ and go to point 2)
    b) if found </div>
           if $nesting_counter > 0
               $nesting_counter-- and go to point 2)
           else
               you've found the closing tag for your `<div class="remove">`. remember current position and just remove that substring.