How can I get parameters from a URL string?

I have an HTML form field $_POST["url"], having some URL strings as the value.

Example values are:

https://example.com/test/1234?email=[e-mail]
https://example.com/test/1234?basic=2&email=[e-mail]
https://example.com/test/1234?email=[e-mail]
https://example.com/test/1234?email=[e-mail]&testin=123
https://example.com/test/the-page-here/1234?someurl=key&email=[e-mail]

etc.

How can I get only the email parameter from these URLs/values?

Please note that I am not getting these strings from the browser address bar.

Answer

You can use the parse_url() and parse_str() for that.

$parts = parse_url($url);
parse_str($parts['query'], $query);
echo $query['email'];

If you want to get the $url dynamically with PHP, take a look at this question:

Get the full URL in PHP