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: <pre> https://example.com/test/1234?email=xyz@test.com https://example.com/test/1234?basic=2&email=xyz2@test.com https://example.com/test/1234?email=xyz3@test.com https://example.com/test/1234?email=xyz4@test.com&testin=123 https://example.com/test/the-page-here/1234?someurl=key&email=xyz5@test.com </pre> 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.