SSIs don't work from within Perl scripts (least
I've never known them too). They only work
within static documents, because the web server,
when it gets a request for a Perl script, hands
off control to perl, which is then expected
to basically just write its output back to the
client.
The server doesn't actually parse
the HTML written by the Perl script (as compared
to when you use SSIs in a server-parsed HTML
file, when the server parses the file to find
any SSIs), so your SSIs won't get expanded if
you try to include them in the HTML outputted
by a Perl script.
