$str = '<a href="search.php" class="left back">back<span class="arrow_btn"></span></a>'; echo preg_replace('/<a href="search.php" class="(.*?)">(.*?)<span class="arrow_btn"><\/span><\/a>/si', '<a href="search.php" class="my class">skip<span class="arrow_btn"></span></a>', $str);
$str = '<a href="search.php" class="left back">back<span class="arrow_btn"></span></a>'; echo str_replace(array('class="left back"', "back"), array('class="my class"', "skip"), $str);