stardiviner <numbchild@gmail.com> wrote:
> I hope a function can subtract two timestamps:
>
>     00:12:35 - 00:10:45 = 00:01:50
>
> Is there some hints or suggestion like function name or Emacs library or package?

> Or Linux command is acceptable. I can write a function to execute shell command then parse the result.

OMG!  Since when that started to require anything but arithmetics?

	(defun timestamp-interval (a b)
	  (cl-flet* ((hms->s (h m s) (+ (* 3600 h)
	                                (* 60 m)
	                                s))
	             (s->hms (s) (let* ((h (/ s 3600))
	                                (s (% s 3600))
	                                (m (/ s 60))
	                                (s (% s 60)))
	                           (list h m s)))
	             (timestamp->s (string) (apply #'hms->s
	                                           (mapcar #'string-to-number
	                                                   (split-string string ":"))))
	             (s->timestamp (s) (apply #'format "%s%02d:%02d:%02d"
	                                      (if (> 0 s) "-" "") (s->hms (abs s)))))
	    (s->timestamp (- (timestamp->s a) (timestamp->s b)))))
	
	(timestamp-interval "00:12:35" "00:10:45")
	;; => "00:01:50"

(Not tested.)


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