(tar) Date input formats

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 Date input formats
 ******************
 
    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 `getdate'
 function) is not described here.
 
    Although the date syntax here can represent any possible time since
 the year zero, computer integers often cannot represent such a wide
 range of time.  On POSIX systems, the clock starts at 1970-01-01
 00:00:00 UTC: POSIX does not require support for times before the POSIX
 Epoch and times far in the future.  Traditional Unix systems have
 32-bit signed `time_t' and can represent times from 1901-12-13 20:45:52
 through 2038-01-19 03:14:07 UTC.  Systems with 64-bit signed `time_t'
 can represent all the times in the known lifetime of the universe.
 

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* General date syntax            Common rules.
* Calendar date items            19 Dec 1994.
* Time of day items              9:20pm.
* Time zone items                EST, PDT, GMT, ...
* Day of week items              Monday and others.
* Relative items in date strings next tuesday, 2 years ago.
* Pure numbers in date strings   19931219, 1440.
* Authors of getdate             Bellovin, Eggert, Salz, Berets, et al.
 

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