PHP利用正则表达式将相对路径转成绝对路径的方法

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<a href="/" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" > / </a>
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<a href="/index.html?id=1" rel="external nofollow" > /index.html?id=1 </a>
<a href="?id=2" rel="external nofollow" > ?id=2 </a>
<!-- // -->
<a href="//index.html" rel="external nofollow" > //index.html </a>
<a href="//www.mafutian.net" rel="external nofollow" > //www.mafutian.net </a>
<!-- 站内链接 -->
<a href="http://www.hole_1.com/index.html" rel="external nofollow" > //m.sbmmt.com/ </a>
<!-- 站外链接 -->
<a href="http://www.mafutian.net" rel="external nofollow" > //m.sbmmt.com/ </a>
<a href="http://www.numberer.net" rel="external nofollow" > //m.sbmmt.com/ </a>
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<a href="1.png" rel="external nofollow" > 1.png </a>
<a href="1.txt" rel="external nofollow" > 1.txt </a>
<!-- 普通链接 -->
<a href="index.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" > index.html </a>
<a href="index.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" > index.html </a>
<a href="./index.html" rel="external nofollow" > ./index.html </a>
<a href="../index.html" rel="external nofollow" > ../index.html </a>
<a href=".../" rel="external nofollow" > .../ </a>
<a href="..." rel="external nofollow" > ... </a>
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<a href="javascript:void(0)" rel="external nofollow" > javascript:void(0) </a>
<a href="a:b" rel="external nofollow" > a:b </a>
<a href="/a#a:b" rel="external nofollow" > /a#a:b </a>
<a href="mailto:&#39;mafutian@126.com&#39;" rel="external nofollow" > mailto:&#39;mafutian@126.com&#39; </a>
<a href="/tencent://message/?uin=335134463" rel="external nofollow" > /tencent://message/?uin=335134463 </a> 
<!-- 相对路径 -->
<a href="." rel="external nofollow" > . </a>
<a href=".." rel="external nofollow" > .. </a>
<a href="../" rel="external nofollow" > ../ </a>
<a href="/a/b/.." rel="external nofollow" > /a/b/.. </a>
<a href="/a" rel="external nofollow" > /a </a>
<a href="./b" rel="external nofollow" > ./b </a>
<a href="./././././././././b" rel="external nofollow" > ./././././././././b </a> <!-- 其实就是 ./b -->
<a href="../c" rel="external nofollow" > ../c </a>
<a href="../../d" rel="external nofollow" > ../../d </a>
<a href="../a/../b/c/../d" rel="external nofollow" > ../a/../b/c/../d </a>
<a href="./../e" rel="external nofollow" > ./../e </a>
<a href="http://www.hole_1.org/./../e" rel="external nofollow" > //m.sbmmt.com/ </a> 
<a href="./.././f" rel="external nofollow" > ./.././f </a>
<a href="http://www.hole_1.org/../a/.../../b/c/../d/.." rel="external nofollow" > //m.sbmmt.com/ </a> 
<!-- 带有端口号 -->
<a href=":8081/index.html" rel="external nofollow" > :8081/index.html </a>
<a href="http://www.mafutian.net:80/index.html" rel="external nofollow" > :80/index.html </a>
<a href="http://www.mafutian.net:8081/index.html" rel="external nofollow" > //m.sbmmt.com/:8081/index.html </a>
<a href="http://www.mafutian.net:8082/index.html" rel="external nofollow" > //m.sbmmt.com/:8082/index.html </a>

http:// ... / ../ ../

function url_to_absolute($relative)
{
 $absolute = '';
 // 去除所有的 './'
 $absolute = preg_replace(&#39;/(?<!\.)\.\//&#39;,&#39;&#39;,$relative);
 $count = preg_match_all(&#39;/(?<!\/)\/([^\/]{1,}?)\/\.\.\//&#39;,$absolute,$res);
 // 迭代去除所有的 &#39;/abc/../&#39;
 do
 {
 $absolute = preg_replace(&#39;/(?<!\/)\/([^\/]{1,}?)\/\.\.\//&#39;,&#39;/&#39;,$absolute);
 $count = preg_match_all(&#39;/(?<!\/)\/([^\/]{1,}?)\/\.\.\//&#39;,$absolute,$res); 
 }while($count >= 1);
 // 除去最后的 &#39;/..&#39;
 $absolute = preg_replace(&#39;/(?<!\/)\/([^\/]{1,}?)\/\.\.$/&#39;,&#39;/&#39;,$absolute);
 $absolute = preg_replace(&#39;/\/\.\.$/&#39;,&#39;&#39;,$absolute);
 // 除去存在的 &#39;../&#39;
 $absolute = preg_replace(&#39;/(?<!\.)\.\.\//&#39;,&#39;&#39;,$absolute);
 return $absolute;
}
$relative = &#39;http://www.mytest.org/../a/.../../b/c/../d/..&#39;;
var_dump(url_to_absolute($relative));
// 输出：string &#39;http://www.mytest.org/a/b/&#39; (length=26)