1 Reading Date and Time
(current-time) => (21209 38073 267139)
The first two numbers are the high and low bits of an integer number giving seconds since the epoch (0:00 January 1, 1970 UTC). The last number is microseconds and may be ommitted. There may be a fourth number representing picoseconds.
decode-time puts this into a more user friendly format:
(decode-time (current-time)) => (30 38 20 17 1 2014 5 nil 0)
The individual values are (SEC MINUTE HOUR DAY MONTH YEAR DOW DST ZONE) DOW is DOW of week DST is t if Daylight saving time is in effect ZONE is an integer indicating the number of seconds east of Greenwich.
format-time-string gives a more everyday format:
(format-time-string "%d/%m/%Y %H:%M:%S" (current-time)) => "17/01/2014 20:38:43"
Or, if you’re really in a hurry:
(current-time-string) => "Fri Jan 17 20:38:54 2014"
2 Setting a Date or Time
(date-to-time "May 20 2011 19:30:00") => (19926 45864)
Note that the date strings format is dependent on your machine’s locale settings. For example, the following may be necessary. For more about locales, read this post.
(date-to-time "20 May 2011 19:30:00")
Enter a date using parse-time-string
(setq concert (parse-time-string "May 20 2011 19:30:00")) => (0 30 19 20 5 2011 nil nil nil)
Unlike date-to-time, parse-time-string allows you to omit the time value :
(setq birthday (parse-time-string "July 29 1953")) => (nil nil nil 29 7 1953 nil nil nil)
Here are some times:
(setq five-seconds (seconds-to-time 5)) (setq ninety-minutes (seconds-to-time (* 60 90))) (setq one-day (seconds-to-time (* 60 60 24)))
The last can be more easily entered as:
(setq one-day (days-to-time 1))
Which leads to
(setq one-week (days-to-time 7))
and so on…
3 Converting Time Values
(encode-time 0 30 19 20 5 2011) => (19926 45864) (decode-time '(19926 45864)) => (0 30 19 20 5 2011 5 t 3600)
4 Calculations on Dates and Times
Here’s the time a concert starts
(setq concert (date-to-time "May 20 2011 19:30:00"))
Suppose the concert lasts two hours (or 2 x 60 x 60 seconds). You can work out the time the concert ends as follows
(time-add concert (seconds-to-time (* 2 60 60)))
Let’s just check that worked
(format-time-string "%d/%m/%Y %H:%M:%S" (time-add concert (seconds-to-time (* 2 60 60)))) => "20/05/2011 21:30:00"
Suppose you know the start and end times of the concert. Use time-subtract to work out the duration:
(setq concert-start (date-to-time "May 20 2011 19:30:00")) (setq concert-end (date-to-time "May 20 2011 22:25:00")) (format-time-string "%H:%M:%S"(time-subtract concert-end concert-start)) => "02:55:00"
Tony Ballantyne Tech 