Is there a way to cause AUCTeX to automatically generate the line

%%% TeX-engine: luatex

in a new .tex document as it does with other file-variables, such as TeX-master?

  • 1
    So you prefer a per-document setting rather than making luatex the default engine just for you? (I think this is a good way to go). Note that if you try to compile a document that loads fontspec package, AUCTeX will ask you to select a proper engine
    – giordano
    May 31, 2017 at 19:14
  • @giordano: What do you mean by 'I think this is a good way to go'? That the per-document setting is a good way to go, or that making luatex the default engine just for me is a good way to go?
    – Evan Aad
    May 31, 2017 at 19:25
  • 1
    The former, because you don't rely on people's default options :-)
    – giordano
    May 31, 2017 at 19:27
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    With a recent version of AUCTeX, do C-c C-m usepackage RET fontspec RET in your .tex file and AUCTeX will ask you for an engine with completion incl. adding your choice to your file. May 31, 2017 at 20:10
  • 1
    Yes, I got your question (and provided an answer ;-), and yes, I know that fontspec is not mandatory (like it isn't mandatory to set any font with pdftex), but it's often used.
    – giordano
    May 31, 2017 at 23:41

1 Answer 1


Add the following code to your init file:

 (lambda ()
   (when (eq major-mode 'latex-mode)
     ;; Check if we are looking at a new or shared file.
     (when (or (not (file-exists-p (buffer-file-name)))
           (eq TeX-master 'shared))
    (intern (completing-read "Add TeX-engine with value: "
                 (mapcar 'car (TeX-engine-alist)) nil nil nil nil "default"))))
     (TeX-update-style t))))

This is inspired by how AUCTeX asks you for master file when you create a new file.

  • Thank you. And to set LuaTeX as the Emacs-wide default, the following line should be added to .emacs, right? (setq-default TeX-engine 'luatex)
    – Evan Aad
    Jun 1, 2017 at 5:40
  • Also: could you please modify your answer so that if I simply hit Enter in reply to the question Add TeX-engine with value: without specifying a value, the current default value (pdfTeX?) will be selected, or better yet, the TeX-engine file-variable won't get written at all, which is the current behavior?
    – Evan Aad
    Jun 1, 2017 at 6:01
  • 1
    I've updated the answer so that `default' is the default engine (also because it's slightly simpler than adding nothing with empty input). BTW, you should also check out an autocompletion package like helm & Co ;-)
    – giordano
    Jun 1, 2017 at 8:01
  • Thank you very much. By the way, I've just noticed something. The mode file-variable is set automatically to latex regardless of the TeX-engine setting. Is this the correct behavior? To make the question more concrete, if my .tex document is written in the LuaLaTeX dialect and I wish to compile it with the luatex program, is it enough to set the TeX-engine file-variable to luatex or will the fact that the mode file-variable is set to latex cause any trouble? Does the mode file-variable definition need to be deleted, or changed, say, to lualatex?
    – Evan Aad
    Jun 1, 2017 at 8:17
  • 2
    latex-mode is to distinguish between plain TeX, LaTeX, docTeX, ConTeXt, TeXinfo, see gnu.org/software/auctex/manual/auctex.html#Modes-and-Hooks It has nothing to do with the actual engine used ;-) AUCTeX is one of the few editors I know that correctly keeps the language and the engine used separated: e.g., you can compile with luatex engine a plain TeX document.
    – giordano
    Jun 1, 2017 at 8:33

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