<?php$a = 'https://img.alicdn.com/tfscom/i5/TB16AE1aIic_eJjSZFnYXFVwVXa_M2.SS2_540x540q90.jpg';preg_match('/_[\d]+x[\d]+/', $a, $match);var_dump($match);$a = preg_replace('/_[\d]+x[\d]+/', '_200x200', $a);var_dump($a);