I'm trying to write a forum-like simple cgi to get feedback from customers who visited my site.

I had this code:
if ($request_method eq "GET") {
  $query_string = $ENV{'QUERY_STRING'};
} elsif ($request_method eq "POST") {
   read (STDIN, $query_string, $ENV{'CONTENT_LENGTH'});
to handle both "POST" or "GET" method.

But when it runs, "GET" works; but "POST" doesn't.

After a while, I realised it was $ENV{'CONTENT_LENGTH'} that created the error. How come? I thought that was standard stuff?