The Problem of Quotes When Parsing Attributes
Using Regular Expressions in PHP

Attribute quotes can be not only double, but also single:

<img src="1.png">
<img src='2.png'>

Let's account for this in our regular expression:

<?php
	preg_match_all('#src\s*=\s*(["\'])(.+?)\1#su', $str, $matches, PREG_PATTERN_ORDER);
?>

Let's check that everything works:

<?php
	var_dump($matches[2]);
?>

Find the contents of all href attributes:

<a href="page1.html">link1</a>
<a href='page2.html'>link2</a>
<a href =  'page3.html'>link3</a>