Functions for inserting a timestamp in several different ways on Emacs

insert-timestamp.el

;; M-x insert-timestamp-default (またはM-x its)で Wed Feb 17 22:18:46 2021
;; M-x insert-timestamp-htmlcomment (またはM-x itsh)で <!-- 2021-02-17 22:18:52 +09:00 --> (と改行)
;; M-x insert-timestamp-unixtime (またはM-x itsu)で 1613567937
;; M-x insert-timestamp-iso (またはM-x itsi)で 2021-02-17T22:19:01+09:00

(defun insert-timestamp-default ()
  "Insert the current timestamp"
  (interactive)
  (insert (current-time-string)))
(defalias 'its 'insert-timestamp-default)

(defun insert-timestamp-htmlcomment ()
  "Insert the current timestamp (HTML comment)"
  (interactive)
  (insert
   (concat
    "<!-- "
    (format-time-string "%Y-%m-%d %T ")
    ((lambda (x) (concat (substring x 0 3) ":" (substring x 3 5)))
     (format-time-string "%z"))
    " -->\n")))
(defalias 'itsh 'insert-timestamp-htmlcomment)

(defun insert-timestamp-unixtime ()
  "Insert the current Unix time"
  (interactive)
  (let ((time (current-time)))
    (let ((time1 (car time))
          (time2 (car (cdr time))))
      (insert (format "%d" (+ (* 65536 time1) time2))))))
(defalias 'itsu 'insert-timestamp-unixtime)

(defun insert-timestamp-iso ()
  "Insert the current timestamp (ISO 8601 format)"
  (interactive)
  (insert
   (concat
    (format-time-string "%Y-%m-%dT%T")
    ((lambda (x) (concat (substring x 0 3) ":" (substring x 3 5)))
     (format-time-string "%z")))))
(defalias 'itsi 'insert-timestamp-iso)
(defalias 'itsiso 'insert-timestamp-iso)