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Merge getdate documentation changes from coreutils.

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Paul Eggert
2004-04-05 05:46:08 +00:00
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ChangeLog
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@@ -1,5 +1,10 @@
2004-04-04 Paul Eggert <eggert@twinsun.com>
Merge getdate documentation changes from coreutils.
* doc/getdate.texi: Update from coreutils CVS.
* doc/tar.texi: Fix getdate menu to match getdate.texi's.
Merge recent gnulib changes, and remove some lint.
Improve support for nanosecond-resolution time stamps.

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doc/getdate.texi
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@@ -1,19 +1,20 @@
@c GNU date syntax documentation
@c Copyright (C) 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002,
@c 2003, 2004 Free Software Foundation, Inc.
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.1 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
@c Texts. A copy of the license is included in the ``GNU Free
@c Documentation License'' file as part of this distribution.
@node Date input formats
@chapter Date input formats
@c Copyright (C) 1994, 1995, 1996, 1997, 1999, 2000, 2001, 2003 Free Software
@c Foundation, Inc.
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.1
@c or any later version published by the Free Software Foundation;
@c with no Invariant Sections, with no
@c Front-Cover Texts, and with no Back-Cover Texts.
@c A copy of the license is included in the section entitled ``GNU
@c Free Documentation License''.
@cindex date input formats
@findex getdate
@findex get_date
First, a quote:
@@ -44,19 +45,7 @@ or a week from Sunday, with feelings of helpless confusion. @dots{}
This section describes the textual date representations that @sc{gnu}
programs accept. These are the strings you, as a user, can supply as
arguments to the various programs. The C interface (via the
@code{getdate} function) is not described here.
@cindex beginning of time, for @acronym{POSIX}
@cindex epoch, for @acronym{POSIX}
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 @acronym{POSIX} systems, the clock starts at 1970-01-01 00:00:00
@sc{utc}: @acronym{POSIX} does not require support for times before the
@acronym{POSIX} Epoch and times far in the future. Traditional Unix systems
have 32-bit signed @code{time_t} and can represent times from 1901-12-13
20:45:52 through 2038-01-19 03:14:07 @sc{utc}. Systems with 64-bit
signed @code{time_t} can represent all the times in the known
lifetime of the universe.
@code{get_date} function) is not described here.
@menu
* General date syntax:: Common rules.
@@ -66,7 +55,8 @@ lifetime of the universe.
* 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.
* Seconds since the Epoch:: @@1078100502.
* Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
@end menu
@@ -128,15 +118,17 @@ ways to do this:
@example
$ LC_ALL=C TZ=UTC0 date
Fri Dec 15 19:48:05 UTC 2000
$ TZ=UTC0 date +"%Y-%m-%d %H:%M:%SZ"
2000-12-15 19:48:05Z
$ date --iso-8601=seconds # a GNU extension
2000-12-15T11:48:05-0800
$ date --rfc-822 # a GNU extension
Fri, 15 Dec 2000 11:48:05 -0800
$ date +"%Y-%m-%d %H:%M:%S %z" # %z is a GNU extension.
2000-12-15 11:48:05 -0800
Mon Mar 1 00:21:42 UTC 2004
$ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ'
2004-03-01 00:21:42Z
$ date --iso-8601=ns # a GNU extension
2004-02-29T16:21:42,692722128-0800
$ date --rfc-2822 # a GNU extension
Sun, 29 Feb 2004 16:21:42 -0800
$ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension.
2004-02-29 16:21:42 -0800
$ date +'@@%s.%N' # %s and %N are GNU extensions.
@@1078100502.692722128
@end example
@cindex case, ignored in dates
@@ -227,7 +219,7 @@ A @dfn{time of day item} in date strings specifies the time on a given
day. Here are some examples, all of which represent the same time:
@example
20:02:0
20:02:00.000000
20:02
8:02pm
20:02-0500 # In @sc{est} (U.S. Eastern Standard Time).
@@ -236,7 +228,9 @@ day. Here are some examples, all of which represent the same time:
More generally, the time of the day may be given as
@samp{@var{hour}:@var{minute}:@var{second}}, where @var{hour} is
a number between 0 and 23, @var{minute} is a number between 0 and
59, and @var{second} is a number between 0 and 59. Alternatively,
59, and @var{second} is a number between 0 and 59 possibly followed by
@samp{.} or @samp{,} and a fraction containing one or more digits.
Alternatively,
@samp{:@var{second}} can be omitted, in which case it is taken to
be zero.
@@ -381,6 +375,26 @@ When a relative item causes the resulting date to cross a boundary
where the clocks were adjusted, typically for daylight-saving time,
the resulting date and time are adjusted accordingly.
The fuzz in units can cause problems with relative items. For
example, @samp{2003-07-31 -1 month} might evaluate to 2003-07-01,
because 2003-06-31 is an invalid date. To determine the previous
month more reliably, you can ask for the month before the 15th of the
current month. For example:
@example
$ date -R
Thu, 31 Jul 2003 13:02:39 -0700
$ date --date='-1 month' +'Last month was %B?'
Last month was July?
$ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!'
Last month was June!
@end example
Also, take care when manipulating dates around clock changes such as
daylight saving leaps. In a few cases these have added or subtracted
as much as 24 hours from the clock, so it is often wise to adopt
universal time by setting the @env{TZ} environment variable to
@samp{UTC0} before embarking on calendrical calculations.
@node Pure numbers in date strings
@section Pure numbers in date strings
@@ -406,10 +420,42 @@ in the date string, but no relative item, then the number overrides the
year.
@node Authors of getdate
@section Authors of @code{getdate}
@node Seconds since the Epoch
@section Seconds since the Epoch
@cindex authors of @code{getdate}
If you precede a number with @samp{@@}, it represents an internal time
stamp as a count of seconds. The number can contain an internal
decimal point (either @samp{.} or @samp{,}); any excess precision not
supported by the internal representation is truncated toward minus
infinity.
@cindex beginning of time, for @acronym{POSIX}
@cindex epoch, for @acronym{POSIX}
Internally, computer times are represented as a count of seconds since
an epoch---a well-defined point of time. On @acronym{GNU} and
@acronym{POSIX} systems, the epoch is 1970-01-01 00:00:00 @sc{utc}, so
@samp{@@0} represents this time, @samp{@@1} represents 1970-01-01
00:00:01 @sc{utc}, and so forth. @acronym{GNU} and most other
@acronym{POSIX}-compliant systems support such times as an extension
to @acronym{POSIX}, using negative counts, so that @samp{@@-1}
represents 1969-12-31 23:59:59 @sc{utc}.
Traditional Unix systems count seconds with 32-bit two's-complement
integers and can represent times from 1901-12-13 20:45:52 through
2038-01-19 03:14:07 @sc{utc}. More modern systems use 64-bit counts
of seconds with nanosecond subcounts, and can represent all the times
in the known lifetime of the universe to a resolution of 1 nanosecond.
On most systems, these counts ignore the presence of leap seconds.
For example, on most systems @samp{@@915148799} represents 1998-12-31
23:59:59 @sc{utc}, @samp{@@915148800} represents 1999-01-01 00:00:00
@sc{utc}, and there is no way to represent the intervening leap second
1998-12-31 23:59:60 @sc{utc}.
@node Authors of get_date
@section Authors of @code{get_date}
@cindex authors of @code{get_date}
@cindex Bellovin, Steven M.
@cindex Salz, Rich
@@ -417,7 +463,7 @@ year.
@cindex MacKenzie, David
@cindex Meyering, Jim
@cindex Eggert, Paul
@code{getdate} was originally implemented by Steven M. Bellovin
@code{get_date} was originally implemented by Steven M. Bellovin
(@email{smb@@research.att.com}) while at the University of North Carolina
at Chapel Hill. The code was later tweaked by a couple of people on
Usenet, then completely overhauled by Rich $alz (@email{rsalz@@bbn.com})

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doc/tar.texi
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@@ -503,7 +503,7 @@ This manual is for @acronym{GNU} @command{tar} (version
from archives.
Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
2003 Free Software Foundation, Inc.
2003, 2004 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
@@ -757,7 +757,8 @@ Date input formats
* 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.
* Seconds since the Epoch:: @@1078100502.
* Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
Controlling the Archive Format