This emacs function helps keep a journal.

pensieve.el

;; Pensieve
;; This program helps keep a journal.
;; Last edit: 2012-06-29.
; A journal is simply a list of textfiles, at most one for every
; day.
; Put into your emacs load directory
; Run with M-x pensieve to open a file, ready to write

;Needed features
;* An interactive shell that shows me a list of entries
; from a certain time period.

;The journal folder. This should be set in the .emacs file.
;(setq pensieve-folder "~/Documents/Journal")

;Format for entry filename
(setq pensieve-entry-format "%Y-%m-%d")


;Internal Constants
(setq sep "/")

;; Functions
(defun todays-filename ()
  "The last modification time of a file.
Returned in the format YYYYMMDDHHMMSS."
  (format-time-string pensieve-entry-format))

(defmacro inc (x)
  "increments x by 1."
  `(setq ,x (1+ ,x)))


(defmacro remove-starting-char (string char)
  "removes a char from the start of a string."
  `(if (string= (substring ,string 0 1) ,char)
       (setq ,string (substring ,string 1 (length ,string)))))

(defmacro remove-ending-char (string char)
  "removes a char from the end of a string."
  `(let ((l (length ,string)))
     (if (string= (substring ,string (1- l) l)
		  ,char)
	 (setq ,string (substring ,string 0 (1- l))))))


(defun concat-paths (&rest paths)
  "Given a set of paths concats them.
Makes sure that sep are alright."
  (let ((n (length paths))
	(i 0)
	(concated-path "")
	(path)
	(subpath))
    (while (< i n)
      (setq subpath (nth i paths))
      (if (not (= i 0))
	  (remove-starting-char subpath sep))
      (if (> (length subpath) 0)
	  (progn
	    (remove-ending-char subpath sep)
	    (setq concated-path (concat concated-path
					subpath
					sep))))
      (inc i))
    (remove-ending-char concated-path sep)))


(defun pensieve ()
  "Create's or appends to today's journal entry."
  (interactive)
  (let ((file (concat-paths pensieve-folder (todays-filename))))
    (find-file file)
    (goto-char (point-max))
    (message "Write a pensieve entry...")))