X-Git-Url: https://git.dogcows.com/gitweb?a=blobdiff_plain;f=doc%2Fgetdate.texi;h=1d312a68959e0079b197add55376e6fc117fddd7;hb=21002fe811420acc5ff49cba391e43be48f13047;hp=ced1414ad88cfc3e25710f9880e126a912954e83;hpb=859ba730d580514fdf7ee6081498c01b1c9aa6d9;p=chaz%2Ftar diff --git a/doc/getdate.texi b/doc/getdate.texi index ced1414..1d312a6 100644 --- a/doc/getdate.texi +++ b/doc/getdate.texi @@ -1,8 +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 @cindex date input formats -@findex getdate +@findex get_date First, a quote: @@ -33,19 +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. @@ -55,7 +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 @@ -117,15 +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 @@ -216,7 +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). @@ -225,7 +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. @@ -370,6 +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 @@ -395,10 +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 @@ -406,7 +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})