emacs/init/dot.emacs.el

(setq emacs-config-name
      (let ((config-name (getenv "EMACS_CONFIG")))
        (if config-name
            config-name
          ".emacs.d")))

(setq emacs-config-directory
      (let ((config-dir (getenv "EMACS_CONFIG_DIR")))
        (if config-dir
            (concat config-dir "/" emacs-config-name "/")
          (concat (substitute-in-file-name "~/")
                  emacs-config-name "/"))))

(setq user-emacs-directory emacs-config-directory)

(let ((init-file (expand-file-name "init.el" user-emacs-directory)))
  (when (file-exists-p init-file)
    (load-file init-file)))