If you think about this for a while, then you will realize that it is impossible for you to access any POST parameters before you use the upload hook functionality. The uploaded files are actually part of the POST parameters, so in order to access the POST parameters, you would have to parse the entire POST request (includng the files). After that, what is the point of using the upload hook, since the file is already uploaded and in a temporary file on the server.

The way I got around it is to put the parameters in the URL action of the form as simple query paramaters. Those are accessible to you at any time in the $ENV{QUERY_STRING} variable, and you can fairly easily parse those manually and pull out your parameters before you invoke CGI.pm to parse the POST request.

No need to parse it manually

my $param = do {
   local $ENV{'REQUEST_METHOD'} = 'GET';
   local $ENV{'CONTENT_LENGTH'};
   local @QUERY_PARAM;

   my $cgi = CGI->new();
   
   $cgi->param(...)
};

my $cgi;
if ($param) {
   $cgi = CGI->new(\&hook);
} else {
   $cgi = CGI->new();
}
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Untested, even less so with mod_perl.

Update: Added local @QUERY_PARAM;.

The hook needs to be called when the request is being parsed (i.e. in new), and the request needs to be parsed in order to know what parameters were supplied. .

Fortunately, the QUERY_STRING is parsed before the body is parsed, so you can use param to check parameters from the QUERY_STRING inside of your hook. Unforunately, the CGI request is not passed to the hook, so you'll have to store the CGI request in a "global":

my $cgi;

sub hook {
   return if not $cgi->param(...);
   my (...) = @_;
   ...
}

$cgi = CGI->new(\&hook);
[download]

I thought that by default CGI.pm did not parse the QUERY_STRING if it was a POST request... You actually have to edit the code to get it to parse and combine both the GET and POST parameters together.

Search the source for CGI.pm for the string "Some people want to have their cake and eat it too".

Your right. I looked at the source, but I looked too quickly and mistook something else for the parsing of QUERY_STRING. They'll have to modify their CGI.pm or use my alternate solution.