PHP中有两个方法可以用来解析URL，分别是parse_url和parse_str。
解析 URL，返回其组成部分
mixed parse_url ( string $url [, int $component = -1 ] )
本函数解析一个 URL 并返回一个关联数组，包含在 URL 中出现的各种组成部分。
本函数不是用来验证给定 URL 的合法性的，只是将其分解为下面列出的部分。不完整的 URL 也被接受，parse_url() 会尝试尽量正确地将其解析。
参数
url 要解析的 URL。无效字符将使用 _ 来替换。
component 指定 PHP_URL_SCHEME、 PHP_URL_HOST、 PHP_URL_PORT、 PHP_URL_USER、 PHP_URL_PASS、 PHP_URL_PATH、 PHP_URL_QUERY 或 PHP_URL_FRAGMENT 的其中一个来获取 URL 中指定的部分的 string。 （除了指定为 PHP_URL_PORT 后，将返回一个 integer 的值）。
返回值
对严重不合格的 URL，parse_url() 可能会返回 FALSE。
如果省略了 component 参数，将返回一个关联数组 array，在目前至少会有一个元素在该数组中。数组中可能的键有以下几种：
如果指定了 component 参数， parse_url() 返回一个 string （或在指定为 PHP_URL_PORT 时返回一个 integer）而不是 array。如果 URL 中指定的组成部分不存在，将会返回 NULL。
实例
<?<span>php </span><span>$url</span> = 'http://username:password@hostname/path?arg=value#anchor'<span>; </span><span>print_r</span>(<span>parse_url</span>(<span>$url</span><span>)); </span><span>echo</span> <span>parse_url</span>(<span>$url</span>,<span> PHP_URL_PATH); </span>?>
以上例程会输出：
<span>Array</span><span>
(
[scheme] </span>=><span> http
[host] </span>=><span> hostname
[user] </span>=><span> username
[pass] </span>=><span> password
[path] </span>=> /<span>path
[query] </span>=> arg=<span>value
[fragment] </span>=><span> anchor
)
</span>/path将字符串解析成多个变量
void parse_str ( string $str [, array &$arr ] )
如果 str 是 URL 传递入的查询字符串（query string），则将它解析为变量并设置到当前作用域。
获取当前的 QUERY_STRING，你可以使用 $_SERVER['QUERY_STRING'] 变量。
参数
str 输入的字符串。
arr 如果设置了第二个变量 arr，变量将会以数组元素的形式存入到这个数组，作为替代。、
实例
<?<span>php </span><span>$str</span> = "first=value&arr[]=foo+bar&arr[]=baz"<span>; </span><span>parse_str</span>(<span>$str</span><span>); </span><span>echo</span> <span>$first</span>; <span>//</span><span> value</span> <span>echo</span> <span>$arr</span>[0]; <span>//</span><span> foo bar</span> <span>echo</span> <span>$arr</span>[1]; <span>//</span><span> baz</span> <span>parse_str</span>(<span>$str</span>, <span>$output</span><span>); </span><span>echo</span> <span>$output</span>['first']; <span>//</span><span> value</span> <span>echo</span> <span>$output</span>['arr'][0]; <span>//</span><span> foo bar</span> <span>echo</span> <span>$output</span>['arr'][1]; <span>//</span><span> baz</span> ?>
前一段时间在读php-resque的源码，看到了在其中对这两个的方法的应用，感觉用的很好，用来解析redis链接的设置。
redis链接的格式是：redis://user:pass@host:port/db?option1=val1&option2=val2，是不是和URL一样，所以用以上两个方法很容易解析。
地址： https://github.com/chrisboulton/php-resque/blob/master/lib/Resque/Redis.php
代码如下：
<span>/*</span><span>*
* Parse a DSN string, which can have one of the following formats:
*
* - host:port
* - redis://user:pass@host:port/db?option1=val1&option2=val2
* - tcp://user:pass@host:port/db?option1=val1&option2=val2
*
* Note: the 'user' part of the DSN is not used.
*
* @param string $dsn A DSN string
* @return array An array of DSN compotnents, with 'false' values for any unknown components. e.g.
* [host, port, db, user, pass, options]
</span><span>*/</span>
<span>public</span> <span>static</span> <span>function</span> parseDsn(<span>$dsn</span><span>)
{
</span><span>if</span> (<span>$dsn</span> == ''<span>) {
</span><span>//</span><span> Use a sensible default for an empty DNS string</span>
<span>$dsn</span> = 'redis://' . self::<span>DEFAULT_HOST;
}
</span><span>$parts</span> = <span>parse_url</span>(<span>$dsn</span><span>);
</span><span>//</span><span> Check the URI scheme</span>
<span>$validSchemes</span> = <span>array</span>('redis', 'tcp'<span>);
</span><span>if</span> (<span>isset</span>(<span>$parts</span>['scheme']) && ! <span>in_array</span>(<span>$parts</span>['scheme'], <span>$validSchemes</span><span>)) {
</span><span>throw</span> <span>new</span> \InvalidArgumentException("Invalid DSN. Supported schemes are " . <span>implode</span>(', ', <span>$validSchemes</span><span>));
}
</span><span>//</span><span> Allow simple 'hostname' format, which `parse_url` treats as a path, not host.</span>
<span>if</span> ( ! <span>isset</span>(<span>$parts</span>['host']) && <span>isset</span>(<span>$parts</span>['path'<span>])) {
</span><span>$parts</span>['host'] = <span>$parts</span>['path'<span>];
</span><span>unset</span>(<span>$parts</span>['path'<span>]);
}
</span><span>//</span><span> Extract the port number as an integer</span>
<span>$port</span> = <span>isset</span>(<span>$parts</span>['port']) ? <span>intval</span>(<span>$parts</span>['port']) : self::<span>DEFAULT_PORT;
</span><span>//</span><span> Get the database from the 'path' part of the URI</span>
<span>$database</span> = <span>false</span><span>;
</span><span>if</span> (<span>isset</span>(<span>$parts</span>['path'<span>])) {
</span><span>//</span><span> Strip non-digit chars from path</span>
<span>$database</span> = <span>intval</span>(<span>preg_replace</span>('/[^0-9]/', '', <span>$parts</span>['path'<span>]));
}
</span><span>//</span><span> Extract any 'user' and 'pass' values</span>
<span>$user</span> = <span>isset</span>(<span>$parts</span>['user']) ? <span>$parts</span>['user'] : <span>false</span><span>;
</span><span>$pass</span> = <span>isset</span>(<span>$parts</span>['pass']) ? <span>$parts</span>['pass'] : <span>false</span><span>;
</span><span>//</span><span> Convert the query string into an associative array</span>
<span>$options</span> = <span>array</span><span>();
</span><span>if</span> (<span>isset</span>(<span>$parts</span>['query'<span>])) {
</span><span>//</span><span> Parse the query string into an array</span>
<span>parse_str</span>(<span>$parts</span>['query'], <span>$options</span><span>);
}
</span><span>return</span> <span>array</span><span>(
</span><span>$parts</span>['host'],
<span>$port</span>,
<span>$database</span>,
<span>$user</span>,
<span>$pass</span>,
<span>$options</span>,<span>
);
}</span>
