$re = '/src=\"([^"]+)\"/';
$str = '<img class="my-page__icon-img" src="https://site.com/static/icons/vector/some.svg" alt="Img" width="40" height="40">
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php