GNU bug report logs -
#13372
bug in date with last week calculation
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Reported by: Tomas Dabašinskas <tomas <at> redhat.com>
Date: Mon, 7 Jan 2013 00:50:01 UTC
Severity: normal
Tags: notabug
Done: Pádraig Brady <P <at> draigBrady.com>
Bug is archived. No further changes may be made.
Full log
Message #23 received at 13372 <at> debbugs.gnu.org (full text, mbox):
----- Original Message -----
> You are using %W which is described as:
>
> `%W'
> week number of year, with Monday as first day of week
> (`00'...`53'). Days in a new year preceding the first Monday
> are
> in week zero.
>
> And so:
>
> December 2012
> Mo Tu We Th Fr Sa Su
> 24 25 26 27 28 29 30 <-- week 52
> 31 <-- week 53
> January 2013
> Mo Tu We Th Fr Sa Su
> 1 2 3 4 5 6 <-- week 0
> 7 8 9 10 11 12 13 <-- week 1
> 14 15 16 17 18 19 20 <-- week 2
> 21 22 23 24 25 26 27
> 28 29 30 31
>
> Since you are reporting your current time as Jan 7 then Dec 31 would
> be last week. Dec 31 would be week 53.
>
> $ env TZ=Australia/Sydney date -d 'last week' -R
> Mon, 31 Dec 2012 16:59:04 +1100
>
> And so:
>
> $ env TZ=Australia/Sydney date -d 'last week' +%W
> 53
>
> $ env TZ=Australia/Sydney date -d 'Dec 31 2012 12:00 +0000' +%W
> 53
>
> There are multiple different definitions for week numbers depending
> upon weeks starting on Sunday, starting on Monday, and so forth.
>
> Also related are:
>
> `%U'
> week number of year, with Sunday as the first day of the week
> (`00'...`53'). Days in a new year preceding the first Sunday
> are
> in week zero.
>
> `%V'
> ISO week number, that is, the week number of year, with Monday
> as
> the first day of the week (`01'...`53'). If the week containing
> January 1 has four or more days in the new year, then it is
> considered week 1; otherwise, it is week 53 of the previous
> year,
> and the next week is week 1. (See the ISO 8601 standard.)
>
> You might want to look at the strftime man page for an alternate
> description:
>
> man 3 strftime
>
> %U The week number of the current year as a decimal
> number, range
> 00 to 53, starting with the first Sunday as the first
> day of
> week 01. See also %V and %W.
>
> %V The ISO 8601 week number (see NOTES) of the current
> year as a
> decimal number, range 01 to 53, where week 1 is the
> first week
> that has at least 4 days in the new year. See also
> %U and %W.
> (SU)
>
> %W The week number of the current year as a decimal
> number, range
> 00 to 53, starting with the first Monday as the first
> day of
> week 01.
>
> ISO 8601 Week Dates
> %G, %g, and %V yield values calculated from the week-based
> year defined
> by the ISO 8601 standard. In this system, weeks start on a
> Monday, and
> are numbered from 01, for the first week, up to 52 or 53, for
> the last
> week. Week 1 is the first week where four or more days fall
> within the
> new year (or, synonymously, week 01 is: the first week of the
> year that
> contains a Thursday; or, the week that has 4 January in
> it). When
> three of fewer days of the first calendar week of the new
> year fall
> within that year, then the ISO 8601 week-based system counts
> those days
> as part of week 53 of the preceding year. For example, 1
> January 2010
> is a Friday, meaning that just three days of that calendar
> week fall in
> 2010. Thus, the ISO 8601 week-based system considers these
> days to be
> part of week 53 (%V) of the year 2009 (%G) ; week 01 of ISO
> 8601 year
> 2010 starts on Monday, 4 January 2010.
>
> Perhaps you are looking for the ISO week date %V? And if just doing
> calculations I suggest using UTC.
>
> $ date -u -d 'Dec 31 2012 12:00 +0000' +%V
> 01
>
> The 'ncal' program provides a useful but unusual way to display the
> ISO week numbers:
>
> $ ncal -A 1 -w 12 2012
> December 2012 January 2013
> Su 2 9 16 23 30 6 13 20 27
> Mo 3 10 17 24 31 7 14 21 28
> Tu 4 11 18 25 1 8 15 22 29
> We 5 12 19 26 2 9 16 23 30
> Th 6 13 20 27 3 10 17 24 31
> Fr 7 14 21 28 4 11 18 25
> Sa 1 8 15 22 29 5 12 19 26
> 48 49 50 51 52 1 1 2 3 4 5
>
> You should also read the FAQ:
>
> http://www.gnu.org/software/coreutils/faq/#The-date-command-is-not-working-right_002e
>
> No one is ever happy with week numbers.
>
> Bob
>
Bob, many thanks for in depth explanation! Please close this is not a bug.
--
Tomas Dabašinskas | Engineering Content Services | Red Hat Asia Pacific
☺: tomas | ☎: +61(0)7 3514 8204 | ✉: tomas <at> redhat.com
This bug report was last modified 12 years and 136 days ago.
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