This type of tutorial/question is best to present with an example. Given that I want to set compile-command variable for LaTex mode which applies to all buffer of this mode. (defun set-compile-command-default-in-LaTeX-mode () (set (make-local-variable 'compile-command) ;; create local variable specific to a current buffer (format "" (buffer-file-name)))) (add-hook 'LaTeX-mode-hook 'set-compile-command-default-in-LaTeX-mode)