Emacs Lisp: Parse Date Time

By Xah Lee. Date: . Last updated: .

This page shows you how to parse date time string.

Problem

Write a elisp function. The function will take a string argument that's any of common date time format, example

and output a canonical form 2011-09-02T11:14:11+0200.

Solution

Two builtin lib to parse datetime:

(parse-time-string STRING) return a list like this: (SEC MIN HOUR DAY MON YEAR DOW DST TZ)

any values that are unknown are returned as nil. in emacs 27, unknown DST value is returned as -1.

(iso8601-parse STRING &optional FORM) return the same format. iso8601-parse is designed for parsing ISO 1601 time formats.

Supported Formats of parse-time-string

;; testing what time formats parse-time-string supports
;; As of GNU Emacs 27.1 of 2020-08-11

(require 'parse-time)

;; parse-time-string returns
;; (SEC MIN HOUR DAY MON YEAR DOW DST TZ)
;; if a element is nil or -1, it means unknown

(parse-time-string "Date: Mon, 01 Aug 2011 12:24:51 -0400")
;; (51 24 12 1 8 2011 1 -1 -14400)
;; yes

(parse-time-string "Local: Mon, Aug 1 2011 9:24 am")
;; (0 24 9 1 8 2011 1 -1 nil)
;; yes

(parse-time-string "2007, August 1")
;; (nil nil nil 1 8 2007 nil -1 nil)
;; yes

(parse-time-string "August 1, 2007")
;; (nil nil nil 1 8 2007 nil -1 nil)
;; yes

(parse-time-string "august 1, 2007")
;; (nil nil nil 1 8 2007 nil -1 nil)
;; yes

(parse-time-string "August 1st, 2007")
;; (nil nil nil nil 8 2007 nil -1 nil)
;; no. The date is nil

(parse-time-string "aug 1, 2007")
(nil nil nil 1 8 2007 nil -1 nil)
;; yes

(parse-time-string "1 aug, 2007")
;; (nil nil nil 1 8 2007 nil -1 nil)
;; yes

(parse-time-string "8/1/2007")
;; (nil nil nil 8 nil 2001 nil -1 nil)
;; no. Takes the 8 as date, 1 as nil

(parse-time-string "08/01/2007")
;; (nil nil nil 8 nil 2001 nil -1 nil)
;; no. Takes the 8 as date, 1 as nil

(parse-time-string "8,1,2007")
(nil nil nil 8 nil 2001 nil -1 nil)
;; no

(parse-time-string "2007-08-01")
;; (nil nil nil 1 8 2007 nil -1 nil)
;; yes

(parse-time-string "2007")
;; (nil nil nil nil nil 2007 nil -1 nil)
;; yes

(parse-time-string "2007-08")
;; (nil nil nil nil nil nil nil -1 nil)
;; no

(parse-time-string "2011-08-01T11:55:37-07:00")
;; (nil nil nil nil nil nil nil -1 nil)
;; no

Datetime Parser Function

Emacs Lisp: xah-fix-datetime

Datetime

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