I use a function like that here:
https://github.com/jkitchin/jmax/blob/master/techela/techela-grade.el#L182
and to set the filetag as you suggest you would call it like this:
#+BEGIN_SRC emacs-lisp
(gb-set-filetag "DATE" (format-time-string "%b %d %Y, %a" (current-time)))
#+END_SRC
You could put that in some hook function if you like.
Kaushal writes:
>> Why don't you just use a timestamp?
>
> But that would need me to insert the timestamp manually each time before
> exports
>
>> You can update whenever you want or using
>> (org-insert-time-stamp (current-time))
>> at the right spot.
>
> Wouldn't that too need manual navigation to #+date: and then eval that
> elisp form?
--
Professor John Kitchin
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@johnkitchin
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