GNU bug report logs - #9283
date increment failure for 2011-10-30

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

From: mike1.lee <at> hsbcib.com
To: bug-coreutils <at> gnu.org
Subject: date increment failure for 2011-10-30
Date: Thu, 11 Aug 2011 11:52:20 +0100

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

Here's what I found adding +1 days to a 2011-10-30
(BTW this is not a problem for any other date I tried)


fut=$(date -d"2011-10-30" '+%F') ;
echo $fut
2011-10-30


fut=$(date -d"$fut +1 days" '+%F') ;
echo $fut
2011-10-30


fut=$(date -d"$fut +2 days" '+%F') ;
echo $fut
2011-10-31


Is this reproducable for anyone else ?

uname -a
Linux xxxxxxxxx  2.6.16.60-0.58.1-smp #1 SMP Wed Dec 2 12:27:56 UTC 2009 
x86_64 x86_64 x86_64 GNU/Linux


Regards,
Mike


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Registered in England - Number 14259
Authorised and regulated by the Financial Services Authority
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Message #8 received at 9283 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: mike1.lee <at> hsbcib.com
Cc: 9283 <at> debbugs.gnu.org
Subject: Re: bug#9283: date increment failure for 2011-10-30
Date: Thu, 11 Aug 2011 10:08:22 -0700

My guess is that, in your time zone, 24 hours after midnight
on 10-30 is indeed 10-31, due to daylight-saving switch.
You can verify this by running 'date' without the '+' option.

Message #13 received at 9283-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: mike1.lee <at> hsbcib.com
Cc: 9283-done <at> debbugs.gnu.org
Subject: Re: bug#9283: date increment failure for 2011-10-30
Date: Thu, 11 Aug 2011 10:48:38 -0600

tag 9283 notabug
thanks

On 08/11/2011 04:52 AM, mike1.lee <at> hsbcib.com wrote:
> Here's what I found adding +1 days to a 2011-10-30
> (BTW this is not a problem for any other date I tried)

Thanks for the report.  However, this is not a bug, but a consequence of 
daylight savings in your current choice of timezone.  This is a FAQ:

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

> fut=$(date -d"2011-10-30" '+%F') ;
> echo $fut
> 2011-10-30
>
>
> fut=$(date -d"$fut +1 days" '+%F') ;
> echo $fut
> 2011-10-30

Adding 24 hours to midnight on a day with 25 hours still results in the 
same day, explaining your results.  The FAQ details several options for 
avoiding the issue, such as fixing your calculations to UTC (which does 
not have daylight savings) or basing your computations relative to noon 
instead of midnight (since both a computed 11am and 1pm still fall in 
the right day, if your relative computation was affected by a daylight 
savings adjustment).

> This transmission has been issued by a member of the HSBC Group

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-- 
Eric Blake   eblake <at> redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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