I don't do cgi much, but the last time I messed with it, there was a problem with using $CGI::POST_MAX , in that it will actully start uploading the file and continue until the MAX is exceeded.

That because of the nature of HTTP. If you want the client to receive a HTTP response, you have to wait for his HTTP request, and by the time perl starts reading from STDIN, the webserver has probably received all the data the client had to send.

Some clients don't specify CONTENT_LENGTH.