php preg_replace ignore class attribute if not exist

Question

hello I have the following code :

$content1 = '<img src="image1.png" class="image1"><img src="image2.png"><img src="image3.png" class="image3">';

when I use this code :

preg_replace('~<img\s*.*?\s*class\s*=\s*"([^"]*)"\s*.*?>~i','<img src="image-replaced" class="$1">', $content1);

this is what I get :

<img src="image-replaced" class="image1"><img src="image-replaced" class="image3">

as you can see this <img src="image2.png"> got ignored because it doesn't have a class attribute so it didn't get replaced.
now what I want to do is if img tag has class attribute in it then it get replaced if not then replace it and keep class blank like this:

<img src="image2.png" class="">

I appreciate any help from you.

Answer 1

Instead of using regular expression, you may consider using DOM for this.

$doc = new DOMDocument;
@$doc->loadHTML($content1); // load the HTML data

$imgs = $doc->getElementsByTagName('img');

foreach ($imgs as $img) {
  if ($img->hasAttribute('class')) {
      $img->setAttribute('src', 'image-replaced');
  } else {
      ## Otherwise set an empty class if you desire. 
      $img->setAttribute('class', '');
  }
}

If you must use regular expression, I would consider using a callback:

$str = preg_replace_callback('~<img src="([^"]*)"(?: class="([^"]*)")?>~i', 
  function($m) {
    return '<img src="'.(isset($m[2])?'image-replaced':$m[1]).'" class="'.($m[2]?:'').'">';
  }, $str);

eval.in