I read something about using use CGI ':cgi-lib'; instead of use CGI qw(:standard) to be able to get the parameter list as a hash using Vars, but I don't understand that.

But in your code, you have:

use CGI qw(:standard :cgi);

Try changing it to:

use CGI ':cgi-lib';

Update: I should probably explain what this actually does... see use. Basically, arguments after the package name to 'use' are passed in as arguments to import ... items starting with a colon are calls to load specific sets of functions, as opposed to a single function name. You may want to also read up on Exporter, although CGI doesn't actually use it.