In emacs, how do I build a filename for org capture purposes?

The templates are in a quoted list so nothing inside gets evaluated. Replace the quote with a back-quote and put something like entry (file+olp+datetree ,(concat org-directory "/logbook.org") "JOURNAL") inside. The `,` will cause the `concat` form to be evaluated.

Wow, thanks. Not in a million years of frantic hacking about would I have figured that out.

I am a 7+ years emacs user rolling my custom config from day one, and just recently discovered the back-quote trick. Dont feel bad, emacs just gives and gives!

Thanks. Thing is, once I was directed to the [BackQuote documentation](https://www.reddit.com/r/orgmode/comments/vyavc8/comment/ig1eyro/?utm_source=share&utm_medium=web2x&context=3), it made complete sense. The problem is that prior to being directed there, I didn't even know enough to search for that. Fortunately, many Reddit users, like emacs, just give and give. :-)

> I didn't even know enough to search for that. Same here, I only got to it once I decided to read the elisp info pages front to back!

It's safer to use `file-name-concat` to avoid path building typos.