how to pass a querystring from a CGI to the DCR

System

Hi I am trying to open a new DCR from a cgi perl script:
I am using
var contentType = "$newType";
var redirectUrl = "http://" + location.hostname + "/iw/webdesk/newdcr?area_path=$main_path&source=$source";
var windowName = "new" + contentType;
var windowSettings = "width=600,height=600,status=yes,resizable=yes,toolbar=no,scrollbars=yes";
newWin = window.open(redirectUrl,windowName,windowSettings);

the question is how to parse the query string inside the DCr to get the value of the $source inside the DCR?
Thanks
Nader