$re = '/(?:https?|ftp):\\\\?\/\\\\?\/sun2.[^\s\,]+/i';
$str = '<a aria-label="фотография" onclick="return showPhoto(\'-100714248_457263531\', \'wall-100714248_195733\', {"temp":{"x":"https:\\/\\/sun1.tattelecom-nbc.userapi.com\\/AZsv8R78JOlrmsTJ6NR_NZpKj-RbfbWCPWQ8uA\\/QnMLGnxpnYk.jpg","y":"https:\\/\\/sun1.tattelecom-nbc.userapi.com\\/vtKcPNt6Wazn_vcPkvLAMX1MOhMz_hfRgYx28g\\/cXJNEGEn2Lc.jpg","z":"https:\\/\\/sun2.tattelecom-nbc.userapi.com\\/oZ0evVUqXklp4UGCisHHFRSaNTEfnnJO_A7lTg\\/ZqD22JRrSyw.jpg","x_":["https:\\/\\/sun1.tattelecom-nbc.userapi.com\\/AZsv8R78JOlrmsTJ6NR_NZpKj-RbfbWCPWQ8uA\\/QnMLGnxpnYk",359,604],"y_":["https:\\/\\/sun1.tattelecom-nbc.userapi.com\\/vtKcPNt6Wazn_vcPkvLAMX1MOhMz_hfRgYx28g\\/cXJNEGEn2Lc",480,807],"z_":["https:\\/\\/sun2.tattelecom-nbc.userapi.com\\/oZ0evVUqXklp4UGCisHHFRSaNTEfnnJO_A7lTg\\/ZqD22JRrSyw",587,987],"base":""},"queue":1}, event)" style="width: 68px; height: 115px;background-image: url(https://sun2.tattelecom-nbc.userapi.com/aMS3yYlzjZF3H6GPY1T5oDAeIqZD5uQv4WveMw/7ToUPNMTnmo.jpg);" class="page_post_thumb_wrap image_cover page_post_thumb_last_column fl_l page_post_thumb_not_single" data-photo-id="-100714248_457263531"></a>';
preg_match($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