>Does anyone know of a way to detect the fact that a file upload has exceeded the $CGI::POST_MAX limit, and hence failed, so that an error can be displayed? As the file doesn't actually get uploaded, I presume that the upload error-detection code given in the CGI module wouldn't work in this case.

I have an upload script that relies *solely* on the CGI.pm module, and the script incorporates a "maximum size" testing feature that has worked for me. Here's the snippet I use as the uploaded file is being "read in" during the upload:

$max_size = '100000'; #set your max size value
$totalbytes=0;
open (IMAGESAVE,">$image_upload_directory/$final_name");
while ($bytesread=read ($file,$data,1024)) {
    $totalbytes+=$bytesread;
    if ($totalbytes > $max_size) {
        unlink ("$image_upload_directory/$file_name");
        &FileTooLarge; #call your error sub 
        exit;
    }
    print IMAGESAVE $data;
}
close IMAGESAVE;
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Given the level of knowledge at perlmonks, I may likely find out there's something wrong with the way I've got things set up ;), but as a said, the code above has worked for me for quite awhile.