Disclaimer: haven't read or tried to follow the whole thread.

$query{$sessionname} is trying to access the value of a key in %query, which is not defined in the scope.

Maybe you meant $query->{ $sessionname } which accesses the value of a key in the hashref $query.

But that won't work either since what you seem to be actually trying to access is the object in $query, not a hashref nor a hash of the same name. See the next line where you correctly access the value returned by $query's object method param() with an argument of $sessionname.

There are other questionable things in this code, for example elsif(scalar$query) -- this is unnecessary (you must have done my $query = CGI->new ... somewhere above, right?) and calling scalar() on a scalar is meaningless.

I don't know whether you wrote all this, or copied it from somewhere, or assembled it from things you've found in various places, but it's a mess, and that's obvious without reading the start of this thread. You badly need to read -- and understand -- quite a bit of documentation. See the Perl Data Structures Cookbook, CGI, for starters.

Also, since you have chosen the CGI route, review Ovid's CGI Course - Resurrected and Updated!

And as more generalized friendly suggestions I offer: (1) Dump your IDEs and learn to write Perl code on the command line and in plain text files. (2) Set up a webserver on your local machine so you can test your code locally and don't have to worry about "uploading" and "downloading" anything until it works.

Hope this helps!