Regular Expression to match on any URL parameter value (Perl syntax)

I am struggling to find a pattern that will allow me to select the value portion of a Parameter=Value element of a URL string. I would like it to be generic enough that I could replace the 'Parameter' with any term and retrieve its value. For example, if the URL string is (it always follows this general form): 'http://www.mysite.com/home.aspx?userid=53&transaction=2&viewport=property' I need to be able to the get value portion of userid or transaction or viewport, or whatever selectively. Preferably it would be as easy as adding a parameter name and it matching eveything that follows its = to the &. My attempts to make a general purpose match string ... suck. I cannot use a javascript function or anything, it has to be perl-like regex matching (This is for use with Apache JMeter if you are curious). I suck at regex :-/ Thanks in advance for any help.