Emacs function to update emacs conf from git repo at startup

emacs-conf-auto-git-pull.el

;; This code assume that your emacs conf (.emacs.d) is itself a git repo.
;; This function check at startup if there's updates available, applying
;; `git pull` in that case, and reloading your config (assumed to be in
;; .emacs.d/init.el).
;;
;; Useful when you have multiple machines with a same emacs configuration
;; that you want to keep synchronized (assuming of course that your emacs
;; repo is in some git server).
;;
;; It is also assumed that you don't need to write a password or passphrase
;; to apply any git command.
;;
;; For manual updates, it also provides the key binding `C-c u`. If you don't
;; have the `bind-key` module, you can rewrite the `bind-keys` call to
;;
;;    (global-set-key (kbd "C-c u") 'emacs-conf-upgrade)
;;
;; instead.

(defun current-date ()
  "Human readable current date time."
  (format-time-string "%d-%m-%Y %H:%M:%S"))

(defun emacs-conf-git-status ()
  "Check the git config status."
  (let ((local (shell-command-to-string "git -C ~/.emacs.d rev-parse @{0}"))
        (remote (shell-command-to-string "git -C ~/.emacs.d rev-parse @{u}"))
        (base (shell-command-to-string "git -C ~/.emacs.d merge-base @{0} @{u}")))
    (cond ((string= local remote) 0) ; Up-to-date
          ((string= local base) 1)   ; Need to pull
          ((string= remote base) 2)  ; Need to push
          (t 3))))                   ; Diverge

(defun emacs-conf-git-pull ()
  "Pull emacs conf git repo."
  (call-process-shell-command "git -C ~/.emacs.d pull"))

(defun emacs-conf-upgrade ()
  "Upgrade the Emacs conf from the git repo in case of updates."
  (call-process-shell-command "git -C ~/.emacs.d fetch")
  (message (concat "Emacs conf upgrade try at " (current-date)))
  (let ((status (emacs-conf-git-status)))
    (cond ((= status 1)
           (progn (emacs-conf-git-pull)
                  (if (= (emacs-conf-git-status) 0)
                      (progn
                        (load "~/.emacs.d/init.el")
                        (message "Emacs conf successfully upgraded."))
                    (message "Emacs conf git repo must be checked. Pull already tried.")
                    )))
          ((/= status 0)
           (message "Emacs conf git repo must be manually checked. Need to push or merge."))
          (t (message "Emacs conf is up-to-date")))
    ))

(bind-keys*
 ("C-c u" . emacs-conf-upgrade))

(emacs-conf-upgrade)