Are you just trying to record what parameters (and values) that your script saw? Do you care if you see the original HTTP request?

Once you let CGI parse the parameters, everything you need is in the CGI object. Record what you get before you do anything else.

use CGI;

my $query = CGI->new;  # reads overthing

log( $query );

#....the rest of your program

sub log
    {
    my $q = shift;

    foreach my $param ( $q->param )
        {
        #... however you want to log things
        my @values = $q->param( $param );
        }
    }
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Update: a stray "s" made it into my code, and it has been hunted down and terminated.