Which version of perl are you running?

You can see an example of code at sub DebugCGI, basically

use CGI;
Main( @ARGV );
exit( 0 );
sub Main {
   my $q = CGI->new;
   my $RequestXML = scalar $q->param('RequestXML');
   ...
   print $header, $body;
   return;
}
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List of perl/CGI related reading materials