bug#9283: date increment failure for 2011-10-30

[Eric Blake]

tag 9283 notabug
thanks

On 08/11/2011 04:52 AM, address@hidden 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).

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--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org