正则表达式解析url参数

Question

I'm having trouble retrieving a URL parameter from a string using regular expressions:

An example string could be

some text and http://google.com/?something=this&tag=yahoo.com and more text, and I would like to be able to find yahoo.com from this.

The caveat is that I need to ensure that the string begins with http://google.com, and not just search for &tag=(.*)

preg_match("/google\.com\/.*&tag=(.*) $/", $subject, $matches)

i'm hoping this matches anything with google.com followed by anything, followed by &tag= followed by a space. Ultimately the goal is to parse out all of the tag= values from google.com URLs.

Is there a better way to accomplish this?

Update:

so I have this new regex: /google\.com\/.*(tag=.*)/ but i'm not sure how to get it to end on a space after the URL

Answer 1

get friendly with the parse_url() function!

$pieces = parse_url('some text http://google.com/?something=this&tag=yahoo.com and whatever');
$query = explode('&', $pieces['query']);

parse_str($pieces['query'], $get);
array_walk($get, function(&$item){
    if (!$sp = strpos($item, ' ')) return;
    $item = substr($item, 0, $sp);
});

var_dump($get); // woo!

edit: thanks to Johnathan for the parse_str() function.