$re = '/wid=.*?(?=")/';
$str = '<img class="image-resize" src="http://hugoboss.scene7.com/is/image/hugoboss/test%2Dimg?wid=100&crop=0,0,960,650" name="mainimg" id="mainimg"/>
';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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