Emacs Lisp Date Time Formats
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Emacs Lisp Date Time Formats
Xah Lee, 2010-11-29
A little emacs lisp tips on working with date time.
ISO 8601 Format
Elisp provides a very convenient function “format-time-string” for printing data time. For example, you can write a command to print date in the yyyy-mm-dd format using 「(insert (format-time-string "%Y-%m-%d"))」. Here's the full code:
(defun insert-date () "Insert current date yyyy-mm-dd." (interactive) (when (region-active-p) (delete-region (region-beginning) (region-end) ) ) (insert (format-time-string "%Y-%m-%d")) )
The “region-active-p” may be new in emacs 23. For emacs 22, use 「(and transient-mark-mode mark-active)」.
(defun insert-date-time () "Insert current date-time string in full ISO 8601 format. Example: 2010-11-29T23:23:35-08:00 See: URL `http://en.wikipedia.org/wiki/ISO_8601' " (interactive) (when (region-active-p) (delete-region (region-beginning) (region-end) ) ) (insert (concat (format-time-string "%Y-%m-%dT%T") ((lambda (x) (concat (substring x 0 3) ":" (substring x 3 5))) (format-time-string "%z")))))
“format-time-string” also supports ordinal date format. For example, “2010 Jan 1st” is “2010-001”, and “2010 December 31” is “2010-365”. The code is this:
(format-time-string "%Y-%j") ; "2010-334" for 2010-11-30
Names for Month and Week
You can also print names for month and week, both full name or abbrevation.
(format-time-string "%B %b") ; "November Nov" (format-time-string "%A %a") ; "Tuesday Tue"
Unix time format
To print Unix time format (i.e. number of seconds since 1970-01-01 00:00:00 +0000.), use 「%s」. Like this:
(format-time-string "%s") ; "1291104066"
Documentation of format-time-string
Call “describe-function” to see the inline doc of “format-time-string”. Here's the output:
format-time-string is a built-in function in `C source code'. (format-time-string FORMAT-STRING &optional TIME UNIVERSAL) Use FORMAT-STRING to format the time TIME, or now if omitted. TIME is specified as (HIGH LOW . IGNORED), as returned by `current-time' or `file-attributes'. The obsolete form (HIGH . LOW) is also still accepted. The third, optional, argument UNIVERSAL, if non-nil, means describe TIME as Universal Time; nil means describe TIME in the local time zone. The value is a copy of FORMAT-STRING, but with certain constructs replaced by text that describes the specified date and time in TIME: %Y is the year, %y within the century, %C the century. %G is the year corresponding to the ISO week, %g within the century. %m is the numeric month. %b and %h are the locale's abbreviated month name, %B the full name. %d is the day of the month, zero-padded, %e is blank-padded. %u is the numeric day of week from 1 (Monday) to 7, %w from 0 (Sunday) to 6. %a is the locale's abbreviated name of the day of week, %A the full name. %U is the week number starting on Sunday, %W starting on Monday, %V according to ISO 8601. %j is the day of the year. %H is the hour on a 24-hour clock, %I is on a 12-hour clock, %k is like %H only blank-padded, %l is like %I blank-padded. %p is the locale's equivalent of either AM or PM. %M is the minute. %S is the second. %Z is the time zone name, %z is the numeric form. %s is the number of seconds since 1970-01-01 00:00:00 +0000. %c is the locale's date and time format. %x is the locale's "preferred" date format. %D is like "%m/%d/%y". %R is like "%H:%M", %T is like "%H:%M:%S", %r is like "%I:%M:%S %p". %X is the locale's "preferred" time format. Finally, %n is a newline, %t is a tab, %% is a literal %. Certain flags and modifiers are available with some format controls. The flags are `_', `-', `^' and `#'. For certain characters X, %_X is like %X, but padded with blanks; %-X is like %X, but without padding. %^X is like %X, but with all textual characters up-cased; %#X is like %X, but with letter-case of all textual characters reversed. %NX (where N stands for an integer) is like %X, but takes up at least N (a number) positions. The modifiers are `E' and `O'. For certain characters X, %EX is a locale's alternative version of %X; %OX is like %X, but uses the locale's number symbols. For example, to produce full ISO 8601 format, use "%Y-%m-%dT%T%z".