How to use httpd alias to show a robots.txt file only if robots.txt does not exist.

[nat]

Is it possible to use alias or somethign else in httpd to show a different file ONLY if the file does not exist?

Example:

1. I count more than 50 Slurp requests from many different IPs coming in just 5 seconds. From time to time it causes a high load.

2. ONLY for people who don't have a robots.txt file I want to setup an alias to slow slurp down just a little bit.

Alias /robots.txt /home/myserver/public_html/robots.txt

robots.txt on myserver contains:

User-agent: Slurp
Crawl-delay: 2

The above kills other peoples robots.txt file so that cannot be used.

3. For people who already have a robots.txt file, what is in their file is what should be used.



Right now I can only get it one way or the other. Does anyone know a way to get apache to show a file only if the person doesn't already have a file by the same name in their directory?