Ah, okay, thanks for the info. On Wed, Aug 02, 2017 at 06:48:39PM -0600, Bob Proulx wrote: > Dale Harris wrote: > > Package: coreutils > > Version: 8.26-3 > > Severity: normal > > Tags: upstream > > > > Dear Maintainer, > > > > > > Just trying to figure out what the first, second, third days are of a month. > > > > So for August 2017: > > > > > > August 2017 > > Su Mo Tu We Th Fr Sa > > 1 _2 3 4 5 > > 6 7 8 9 10 11 12 > > 13 14 15 16 17 18 19 > > 20 21 22 23 24 25 26 > > 27 28 29 30 31 > > > > > > This is relative to: Wed Aug 2 17:33:10 EDT 2017 > > > > If do: > > > > date -d 'first monday', I get: Mon Aug 7 00:00:00 EDT 2017 > > The docs say: > > The explicit mention of a day of the week will forward the date (only if > necessary) to reach that day of the week in the future. > > Days of the week may be spelled out in full: ‘Sunday’, ‘Monday’, > ‘Tuesday’, ‘Wednesday’, ‘Thursday’, ‘Friday’ or ‘Saturday’. Days may be > abbreviated to their first three letters, optionally followed by a > period. The special abbreviations ‘Tues’ for ‘Tuesday’, ‘Wednes’ for > ‘Wednesday’ and ‘Thur’ or ‘Thurs’ for ‘Thursday’ are also allowed. > > A number may precede a day of the week item to move forward > supplementary weeks. It is best used in expression like ‘third monday’. > In this context, ‘last DAY’ or ‘next DAY’ is also acceptable; they move > one week before or after the day that DAY by itself would represent. > > Therefore mentioning "1 Monday" (which is what "first monday" is > mapped to) will forward to one Monday in the future. Okay. > > > date -d 'second monday', I get: Mon Aug 7 00:00:01 EDT 2017 > > The word "second" is problematic. The documentation says: > > A few ordinal numbers may be written out in words in some contexts. > This is most useful for specifying day of the week items or relative > items (see below). Among the most commonly used ordinal numbers, the > word ‘last’ stands for -1, ‘this’ stands for 0, and ‘first’ and ‘next’ > both stand for 1. Because the word ‘second’ stands for the unit of time > there is no way to write the ordinal number 2, but for convenience > ‘third’ stands for 3, ‘fourth’ for 4, ‘fifth’ for 5, ‘sixth’ for 6, > ‘seventh’ for 7, ‘eighth’ for 8, ‘ninth’ for 9, ‘tenth’ for 10, > ‘eleventh’ for 11 and ‘twelfth’ for 12. > > The important part is: > > Because the word ‘second’ stands for the unit of time > there is no way to write the ordinal number 2 > > That is why you can't say "second monday". You can only use the > numbers and say "2 Monday". (Don't shoot me. I am only the > messenger.) > > > date -d 'third monday', I get: Mon Aug 21 00:00:00 EDT 2017 > > date -d 'fourth monday', I get: Mon Aug 28 00:00:00 EDT 2017 > > date -d 'fifth monday', I get: Mon Sep 4 00:00:00 EDT 2017 > > All okay. > > I want to note that the default date format for legacy reasons is > ambiguous. It is better to use an unambiguous format such as date -R > which will specify the timezone in a standard format. > > > So I'm a bit confused, if it's relative from the day, I could unstand the > > first Monday being the 7th, but the second Monday should be the 14th. If it > > is inside the month, then this doesn't make any sense because the 7th is the > > first Monday of the month, and 14th the second. What am I missing? > > If doing date calculations it is highly recommended to do them around > 12:00 noon instead of midnight to avoid daylight saving time changes. > Let me specify a timezone explicitly here for the archive and > reproducibility of the case. > > env TZ=US/Mountain date -R -d '1 monday 12:00' > Mon, 07 Aug 2017 12:00:00 -0600 > > env TZ=US/Mountain date -R -d '2 monday 12:00' > Mon, 14 Aug 2017 12:00:00 -0600 > > env TZ=US/Mountain date -R -d '3 monday 12:00' > Mon, 21 Aug 2017 12:00:00 -0600 > > env TZ=US/Mountain date -R -d '4 monday 12:00' > Mon, 28 Aug 2017 12:00:00 -0600 > > Or with with UTC instead. Working with UTC is always recommended. > > date -u -R -d '1 monday' > Mon, 07 Aug 2017 00:00:00 +0000 > > date -u -R -d '2 monday' > Mon, 14 Aug 2017 00:00:00 +0000 > > date -u -R -d '3 monday' > Mon, 21 Aug 2017 00:00:00 +0000 > > date -u -R -d '4 monday' > Mon, 28 Aug 2017 00:00:00 +0000 > > A reference to some of these problem areas. > > > https://www.gnu.org/software/coreutils/faq/coreutils-faq.html#The-date-command-is-not-working-right_002e > > Hopefully this explains the problem. > Bob
-- Dale Harris / Unix System Admin / Generic Network Systems, LLC d...@gnetsys.net +1-212-268-4722 ext. 230 http://www.gnetsys.com/
