How can I access parameters passed in the URL when a form is POSTed to my script?

Answer 1

Change your script to:

use CGI;
use Data::Dumper;

my $query = CGI->new; # even though I'd rather call the object $cgi
print $query->header('text/plain'), Dumper($query);

and take a look at what is being passed to your script and update your question with that information.

Answer 2

If you're doing a POST query, you need to use $query->url_param('action') etc. to get parameters from the query string. You don't need or benefit from the QSA modifier.

Answer 3

You could just look at $ENV{QUERY_STRING} actually. This will tell you exactly what is being passed from the web server to your script after the rewrite has been done, without making use of the CGI module. I think this is a good way to debug this kind of problem.