PHP正则表达式提取html超链接中的href地址

<?php

$preg='/<a .*?href="(.*?)".*?>/is';

$str ='<a href="链接1">URLNAME</a>文本段1<a href="链接2" target="_blank">URLNAME</a>文本段2<a  target="_blank" href="链接3">URLNAME</a>...文本段n';

preg_match_all($preg,$str,$match);//在$str中搜索匹配所有符合$preg加入$match中

for($i=0;$i<count($match[1]);$i++)//逐个输出超链接地址

{

  echo $match[1][$i]."<br />";

}

?>

$str='<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; line-height: 200%;"><img border="0" src="upfiles/2009/07/1246430143_4.jpg" alt=""/></p><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; line-height: 200%;"><img border="0" src="upfiles/2009/07/1246430143_3.jpg" alt=""/></p><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; line-height: 200%;"><img border="0" src="upfiles/2009/07/1246430143_1.jpg" alt=""/></p>'; 

$pattern="/<[img|IMG].*?src=['|"](.*?(?:[.gif|.jpg]))['|"].*?[/]?>/"; 

preg_match_all($pattern,$str,$match); 

print_r($match);