How can I tell when inetd invokes a service (svnserve) I have listed in
my inetd.conf? I would like the system to beep by just executing a
command to beep on the command line which I already know.

This would probably involve writing a shell script that inetd invokes
instead of the service, with the script itself then invoking my service.

I don't know how to write the script. My inetd.conf looks like this...

# Subversion server...
svn stream tcp nowait root /opt/bin/svnserve -i -r /public/svnrepos

What would I replace that with and what would the script look like?