CGI has a debug mode you'll find useful.

>perl -MCGI -MData::Dumper -e"print Dumper { CGI::Vars() }" "a=b&c=d"
$VAR1 = {
          'a' => 'b',
          'c' => 'd'
        };

>perl -MCGI -MData::Dumper -e"print Dumper { CGI::Vars() }" a=b c=d
$VAR1 = {
          'a' => 'b',
          'c' => 'd'
        };
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See the "DEBUGGING" section of CGI for more.