How can I automatically add some local variables info to a C-x C-f new (.tex) file?

Question

I use auctex to edit my .tex files. Each time I create a new file .tex file via C-x C-f, I want to insert two local variables informations:

% Local Variables:
% coding: utf-8-unix
% TeX-engine: luatex
% End:

Until now, I do M-x add-file-local-variable two times. Is there a way to automate this?

Answer 1

You can use a hook to achieve this. Use the one you need as described in auctex documentation. Here we check the file extension so that we don't do that for eg .sty files.  Also, we test the buffer-read-only variable before modifying the buffer.

The goto-char at the end ensures point is set at beginning of buffer.

(defun my/add-auctex-file-variables ()
  (interactive)
  (if (and (not buffer-read-only)
           (string= (file-name-extension (buffer-file-name)) "tex"))
   (progn
     (add-file-local-variable 'coding 'utf-8-unix)
     (add-file-local-variable 'TeX-engine 'luatex)
     (goto-char (point-min)))))

(add-hook 'LaTeX-mode-hook 'my/add-auctex-file-variables)

Also, as can be seen on add-file-local-variable docstring (display it with C-h f add-file-local-variable) any setting of the variable is first deleted, so there's no risk of accumulating such definitions.

A possible pitfall is that the file is marked as modified even if nothing has actually changed.