Where to place org-agenda-files sexp

Question

I have this

(setq org-agenda-files (directory-files-recursively "~/Dropbox/org/journal/" "\\.org$"))

but I don't know where to place it in order to make sure that on the event of a new daily org-journal file creation in my journal directory (e.g. ~Dropbox/org/journal/2021/02/) the agenda file list will immediately be updated. At the moment I have it placed early in my init.el, which thereafter calls a big, general config.org full of package initializations and tweaks, then a private custom-set-variables file. Does this sexp need to be part of some special trigger/hook/event code to know to update the org-agenda-files list when a new org-journal day file appears?

Answer 1

TL;DR: set the variable org-agenda-files to be a list of all the directories that you want to scan recursively for *.org files:

(setq org-agenda-files '("~/Dropbox/org/journal/"))

Explanation:

There are two org-agenda-files objects: a function and a variable. Org mode calls the function when it needs the list. The function looks at the org-agenda-files variable and proceeds accordingly:

• if the variable is a filename, then it is interpreted as a file that contains the names of all the agenda files. So this is static: you need to add any additional files that you want.

• if the variable is a list of filenames, then that's the list of agenda files, except that if an entry in the list is a directory it is scanned recursively for any files that match org-agenda-file-regexp. The latter matches files of the form foo.org so you don't have to do this yourself.

If you look at the implementation of the function org-agenda-files, you'll see that it does already the recursive scan, so you don't have to. And it uses the org-agenda-file-regexp so you don't have to.

Untested.