php用正则表达式匹配URL的简单方法

^(([^:/?#]+):)?(//([^/?#]))?([^?#])(\?([^#]))?(#(.))?
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<?php
$search = '~^(([^:/?#]+):)?(//([^/?#]))?([^?#])(\?([^#]))?(#(.))?~i';
$url = 'https://.jb51./pub/ietf/uri/#Gonn';
$url = trim($url);
preg_match_all($search, $url ,$rr);
printf("<p>输出URL数据为</p><pre>%s</pre>\n",var_export( $rr ,TRUE));

/
各分组如下
      $1 = http:
      $2 = http
      $3 = //.nowamagic.
      $4 = .nowamagic.
      $5 = /pub/ietf/uri/
      $6 = <undefined>
      $7 = <undefined>
      $8 = #Gonn
      $9 = Gonn
/
?>

<?php
// 从 URL 中取得主机名
preg_match("/^(http:\/\/)?([^\/]+)/i", "https://.jb51./index.html", $matches);
$host = $matches[2];
// 从主机名中取得后面两段
preg_match("/[^\.\/]+\.[^\.\/]+$/", $host, $matches);
echo "domain name is: {$matches[0]}\n";
?>