I have used something like this:

(defun gb-set-filetag (tag value)
"Set filetag TAG to VALUE.
If VALUE is nil, remove the filetag."
(save-excursion
(goto-char (point-min))
(if (re-search-forward (format "#\\+%s:" tag) (point-max) 'end)
;; replace existing filetag
(progn
(beginning-of-line)
(kill-line)
(when value
(insert (format "#+%s: %s" tag value))))
;; add new filetag
(if (looking-at "^$") ;empty line
;; at beginning of line
(when value
(insert (format "#+%s: %s" tag value)))
;; at end of some line, so add a new line
(when value
(insert (format "\n#+%s: %s" tag value)))))))
I am not sure what you mean by the end of the headers. This code ends up
putting new keywords at the end of the file. You could add some code I
guess that jumps back to the top, and puts it at the next line after the
last #+ or something.

John

-----------------------------------
Professor John Kitchin
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803
@johnkitchin
http://kitchingroup.cheme.cmu.edu



On Thu, Nov 15, 2018 at 7:14 AM Matt Price <moptop99@gmail.com> wrote:

>
>
> On Sat, Nov 10, 2018 at 1:58 PM Nicolas Goaziou <mail@nicolasgoaziou.fr>
> wrote:
>
>> Hello,
>>
>> John Kitchin <jkitchin@andrew.cmu.edu> writes:
>>
>> > You can retrieve keywords in the org-file like this:
>> >
>> > (defun get-keyword (key)
>> >   (org-element-map (org-element-parse-buffer) 'keyword
>> >     (lambda (k)
>> >       (when (string= key (org-element-property :key k))
>> > (org-element-property :value k)))
>> >     nil t))
>>
>> As a minor addendum,
>>
>>     (org-element-parse-buffer 'element)
>>
>> is more efficient in this case.
>>
>> An even more efficient way to retrieve keywords, assuming buffer is not
>> already parsed, would be:
>>
>>     (org-with-point-at 1
>>       (let ((case-fold-search t)
>>             (regexp (format "^[ \t]*#\\+%s:" key))
>>             (result nil))
>>         (while (re-search-forward regexp nil t)
>>           (let ((element (org-element-at-point)))
>>             (when (eq 'keyword (org-element-type element))
>>               (push (org-element-property :value element) result))))
>>         result))
>>
>> This is very helpful, Nicolas and John.
>
> What about *setting* a global keyword? I would like to write something
> like this:
>
> (defun org-lms-set-global-prop-value (key value)
>   "Add or update keyword KEY in the org file header."
>   (save-excursion
>     (goto-char (point-min))
>     (insert (format "#+%s: %" (upcase key) value))))
>
> But
> (a) insert the value at the *end* of the headers section, not the
> beginning.
> (b) preferably replace any existing values of the keyword rather than
> write a whole new line.
>
> (b) I guess could be achieved with something like
>
> (replace-regexp (format "\(^[ \t]*#\\+%s: \)\(.*\)" key) (concat "\1"
> value))
> But what about (a)? I thought org already had a couple of functions that
> performed this kind of serach but now I'm not so sure.
>
>
>
>
>> Regards,
>>
>> --
>> Nicolas Goaziou
>>
>