<?php $p = '/<img .*?src=[\'|\"](.+?)[\'|\"].*? alt="PHP提取页面第一张图为缩略图的代码" >/i'; preg_match_all($p,$str,$match); print_r($match[1][0]); ?>
<img alt="" src="http://usr.im/200x60?bg=3498DB&text=tool.lu" class="img" /> 结果为：http://usr.im/200x60?bg=3498DB&text=tool.lu <img alt="" src="http://img.mukewang.com/user/55c877240001291602790279-80-80.jpg" class="img" /> 结果为：http://img.mukewang.com/user/55c877240001291602790279-80-80.jpg
