Under Apache, scripts with a name that starts with "nph-" are handled as no-parse-header scripts. Apache doesn't wait to process their output, but rather sends it directly through from your script as you produce it. This was the clasic way of showing activity from a script that produced output over a long period.

The cost, besides the odd name prefix, was that you had to supply all the headers. As I remember, all you need is to output two additional lines at the beginning:

Content Type: text/html
[blank line]
[download]

(The blank line is important.)

I'm not at a computer where I can check this, but I'm sure someone else will add a correction if I remember it wrong, and I can check it in the morning.

I checked this morning, the headers are all provided by CGI.pm. Use

$q = new CGI;
print $q-header();
[download]