Previous stab at this revoked after an experiment with Apache.

I didn't know that an SSI #include would actually invoke scripts, but it does with Apache. Cool.

It appears that Apache isn't passing along the environment variables that CGI.pm needs. But there is something in the environment that you can use. I'll lead you to within sight of it, and from then on you're on your own.

Have your test.shtml invoked the following script:

#!/usr/bin/perl -w
print "Content-type: text/html\n\n";
print "<pre>";
foreach $key ( sort keys %ENV ) {
    print $key, ": ", $ENV{$key}\n";
}
print "</pre>\n";
[download]

I think you'll find something sitting around in the environment that you can use. Witha little trickery, you might even be able to get CGI.pm working, though you'll have to stuff some missing stuff into the environment.

Followup: my well-worn copy of O'Reilly's Webmaster in a Nutshell is out-of-date with respect to #exec vs. #include. Isotope's link below is authoritative (at least if you're running a current version of Apache).