setting http-equiv="Expires" on index pages

Hello,

        I'm looking for a way to set http-equiv="Expires" on the index 
pages. I handle updates to the archive in batches out of cron. I would 
like to set the index pages to expire on the same interval. 

As I see it, there are two ways to accomplish this:

        1) modify the rc file every time I do an update

        2) add an new variable to MHonArc

The first option is fairly straight forward, with a bit of scripting.

The second one I'm not sure about. Would it be feasible to add support 
for user defined variables. What I'm thinking of is the facility to
pass variables to be substituted on the command line. For example, in
a rc file, I would have:

<META http-equiv="Expires" content="$MYDATE$">

Then on the command line, I would say:

        mhonarc -usersub MYDATE "Thu, 18 Mar 1999 14:29:00 JST" ....
        
Regards,

        Andy