(coreutils.info)Date input formats

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29 Date input formats
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First, a quote:

     Our units of temporal measurement, from seconds on up to months,
     are so complicated, asymmetrical and disjunctive so as to make
     coherent mental reckoning in time all but impossible.  Indeed, had
     some tyrannical god contrived to enslave our minds to time, to make
     it all but impossible for us to escape subjection to sodden
     routines and unpleasant surprises, he could hardly have done better
     than handing down our present system.  It is like a set of
     trapezoidal building blocks, with no vertical or horizontal
     surfaces, like a language in which the simplest thought demands
     ornate constructions, useless particles and lengthy
     circumlocutions.  Unlike the more successful patterns of language
     and science, which enable us to face experience boldly or at least
     level-headedly, our system of temporal calculation silently and
     persistently encourages our terror of time.

     ... It is as though architects had to measure length in feet, width
     in meters and height in ells; as though basic instruction manuals
     demanded a knowledge of five different languages.  It is no wonder
     then that we often look into our own immediate past or future, last
     Tuesday or a week from Sunday, with feelings of helpless confusion.
     ...

     —Robert Grudin, ‘Time and the Art of Living’.

   This section describes the textual date representations that GNU
programs accept.  These are the strings you, as a user, can supply as
arguments to the various programs.  The C interface (via the
‘parse_datetime’ function) is not described here.

General date syntax

Common rules.

Calendar date items

19 Dec 1994.

Time of day items

9:20pm.

Time zone items

EST, PDT, UTC, ...

Combined date and time of day items

1972-09-24T20:02:00,000000-0500.

Day of week items

Monday and others.

Relative items in date strings

next tuesday, 2 years ago.

Pure numbers in date strings

19931219, 1440.

Seconds since the Epoch

@1078100502.

Specifying time zone rules

TZ="America/New_York", TZ="UTC0".

Authors of parse_datetime

Bellovin, Eggert, Salz, Berets, et al.