When editing multiple files, AucTeX keeps track of the master file by appending the following to each file:

%%% Local Variables:
%%% mode: latex
%%% TeX-master: "../document"
%%% End:

I'm editing a document with multiple colleagues and I don't want to add this to their files when editing them.

Is there a way to set an AucTeX variable pointing to the path of the master file, and whenever I hit C-c C-c, it will look for that file?

One option is to hit M-: and type (setq-default TeX-master "../document"). Is there a better way than that?


Not sure what AUCTeX does when TeX-master is not set, nowadays, but if you use the default latex-mode that comes with Emacs, the corresponding tex-master is guessed by looking for a nearby buffer with the usual \documentclass thingy. If you keep one document per directory, this is usually all it takes to DTRT and you don't need to set any file-local variable: just make sure you have that main .tex file opened in a buffer in that same Emacs session.

AUCTeX being usually fancier than this builtin latex-mode, I expect it also has some way to guess the right TeX-master. If it doesn't, then I suggest you file a feature-request.

But there are other options:

  • Set the TeX-master from a .dir-locals.el file. To set up a .dir-locals.el file, the best way is through Emacs using M-x add-dir-local-variable.

  • Set the TeX-master via dir-locals-set-class-variables and dir-locals-set-directory-class.

  • Do you all by hand, old-school style:

    (add-hook 'LaTeX-mode-hook
              (lambda ()
                (when (string-prefix-p "/thing/with/colleagues"
                  (setq TeX-master "../document"))))
  • I didn't know about this latex-mode feature. Unfortunately, it seems that AUCTeX doesn't have it. Thanks for the first two suggestions with .dir-local.s.el and dir-locals-set-{class-variables,directory-class}, I haven't use them yet, but I'll look them up. – Yamaneko Sep 12 '18 at 14:33
  • 1
    To set up a .dir-locals.el file, the best way is through Emacs using M-x add-dir-local-variable. I tried to add the absolute path ((latex-mode (TeX-master (concat default-directory "document")))), but I still haven't managed to get it working. When I eval, it outputs t, which is the AUCTeX output when the open file is the master file. By the way, is there a difference between .dir-local.s.el and .dir-locals.el? – Yamaneko Sep 19 '18 at 12:46
  • @Yamaneko: w.r.t to .dir-local.s.el and .dir-locals.el, yes there's a big difference: the first doesn't work (was a typo, thanks!). – Stefan Sep 19 '18 at 13:23
  • Thanks! I wasn't sure. This answer is exactly what I need. As soon as I get it working, I'll accept it. Let me try a couple times more and I'll report later. – Yamaneko Sep 19 '18 at 17:20
  • 1
    @Yamaneko: Also, feel free to improve the answer with a description of how to use add-dir-local-variable. – Stefan Sep 19 '18 at 19:08

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