GNU bug report logs - #23664
Date Problem: Wrong return using last month today (2016-05-31)

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: "Felippe Silvestre" <silvestre <at> redeservice.com.br>
To: <bug-coreutils <at> gnu.org>
Subject: Date Problem: Wrong return using last month today (2016-05-31)
Date: Tue, 31 May 2016 15:14:18 -0300

[Message part 1 (text/plain, inline)]

[root <at> superdssbox999 ~]# date

Tue May 31 15:10:47 BRT 2016

 

[root <at> superdssbox999 ~]# date -d"last month"

Sun May  1 15:10:52 BRT 2016

 

[root <at> superdssbox999 ~]# date -d"last day last month"

Sat Apr 30 15:10:54 BRT 2016

[root <at> superdssbox999 ~]#

 

Atte.

 

Felippe Silvestre

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Message #12 received at 23664-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Felippe Silvestre <silvestre <at> redeservice.com.br>,
 23664-done <at> debbugs.gnu.org
Subject: Re: bug#23664: Date Problem: Wrong return using last month today
 (2016-05-31)
Date: Tue, 31 May 2016 13:32:04 -0600

[Message part 1 (text/plain, inline)]

tag 23664 notabug
thanks

On 05/31/2016 12:14 PM, Felippe Silvestre wrote:
> [root <at> superdssbox999 ~]# date
> 
> Tue May 31 15:10:47 BRT 2016
> 
>  
> 
> [root <at> superdssbox999 ~]# date -d"last month"
> 
> Sun May  1 15:10:52 BRT 2016

You've hit a FAQ; relative date terms like "last month" are easier to
code if they merely add a fixed amount of 30 days, rather than a
variable logical amount, particularly since the amount that would be
variable may depend on things like daylight savings changes.

https://www.gnu.org/software/coreutils/faq/coreutils-faq.html#The-date-command-is-not-working-right_002e

There is work underway to add a 'date --debug' option that will make it
more obvious HOW date is arriving at its results when presented with
inherently ambiguous requests, such as using "last month" near the
boundary of a month.

I'm closing out this particular request in the bug database, since it is
known behavior, but feel free to add more comments or even provide a
reason that it should be reopened if what has been mentioned above is
insufficient to help you with your use of 'date'.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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