.htaccess

Options +ExecCGI
AddHandler perl-script cgi
PerlResponseHandler ModPerl::Registry
PerlOptions +ParseHeaders

RewriteEngine on
RewriteCond %{ENV:REDIRECT_REDIRECT_INTERNAL_ROUTING} !yes
RewriteRule .* routing.cgi [L,E=INTERNAL_ROUTING:yes]

## So, this .htaccess file first redirects all requests to one script 
## called "routing.cgi". It also sets an environment variable called 
## "INTERNAL_ROUTING". Owing to the mod_rewrite redirect, Apache
## "kindly" renames the environment variable immediately to
## "REDIRECT_INTERNAL_ROUTING". 

## The purpose of this environment variable is to prevent infinite 
## recursion if inside of routing.cgi I tell Apache to 
## silently/internally redirect to another file like a .html file. 
## Note: such a redirect will actually be the *second* redirect in 
## the current scope, the first being from mod_rewrite.

## The really amusing part is that the filter to prevent the recursion
## has to inspect an environment variable called 
## "REDIRECT_REDIRECT_INTERNAL_ROUTING", with 2x the "REDIRECT_"
## being prepended, since Apache "sees" two redirects. Ridiculous.

the point of the flag is not to prevent recursion on routing.cgi itself... the [L] flag I believe accomplishes that. The point is to prevent this condition from passing if, from inside routing.cgi, I issue a:

$->internal_redirect_handler("/some/other/file.html");

That internal Apache redirect command will cause the .htaccess to be re-evaluated, which will recurse back into routing.cgi infinitely if I don't find a way for the redirects issued from the Perl to be ignored and not mapped to "routing.cgi". I tried several different things, and was only able to get an environment variable to persist long enough to be useful for this task.

So, the idea is, set an environment variable when the first top-level request from the browser comes in and the request is routed to routing.cgi... then let routing.cgi redirect internally to any file it wants to, and don't cause those redirects to get trapped by the mod_rewrite rules.