+(defun environment (&optional frame)
+ "Return a list of environment variables with their values.
+Each entry in the list is a string of the form NAME=VALUE.
+
+The returned list can not be used to change environment
+variables, only read them. See `setenv' to do that.
+
+If optional parameter FRAME is non-nil, then it should be a
+frame. The function returns the environment of that frame.
+
+The list is constructed by concatenating the elements of
+`process-environment' and the 'environment parameter of the
+selected frame, and removing duplicated and empty values.
+
+Non-ASCII characters are encoded according to the initial value of
+`locale-coding-system', i.e. the elements must normally be decoded for use.
+See `setenv' and `getenv'."
+ (let* ((env (append process-environment
+ ;; (frame-environment frame)
+ nil))
+ (scan env)
+ prev seen)
+ ;; Remove unset variables from the beginning of the list.
+ (while (and env
+ (or (not (stringp (car env)))
+ (not (string-match "=" (car env)))))
+ (or (member (car env) seen)
+ (setq seen (cons (car env) seen)))
+ (setq env (cdr env)
+ scan env))
+ (let (name)
+ (while scan
+ (cond ((or (not (stringp (car scan)))
+ (not (string-match "=" (car scan))))
+ ;; Unset variable.
+ (or (member (car scan) seen)
+ (setq seen (cons (car scan) seen)))
+ (setcdr prev (cdr scan)))
+ ((member (setq name (substring (car scan) 0 (string-match "=" (car scan)))) seen)
+ ;; Duplicated variable.
+ (setcdr prev (cdr scan)))
+ (t
+ ;; New variable.
+ (setq seen (cons name seen))))
+ (setq prev scan
+ scan (cdr scan))))
+ env))
+