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bug#11125: date command calculations are not consistent
From: |
Eric Blake |
Subject: |
bug#11125: date command calculations are not consistent |
Date: |
Thu, 29 Mar 2012 13:06:43 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120316 Thunderbird/11.0 |
On 03/29/2012 12:34 PM, Thomas R. Schaefer wrote:
> In this case date is calculating with 24 hours days regardless of crossing a
> DST boundary..
>
> address@hidden ~]# date -d "Thu Mar 22 00:00:00 CDT 2012 - 21 days"
> Wed Feb 29 23:00:00 CST 2012
This started from one fixed point in time, relative to the 'CDT' time
zone, and subtracted 21 * 24 hours.
>
> In this case date does take DST into account in a relative date operation..
>
> address@hidden ~]# date -d "last Thursday - 21 days"
> Thu Mar 1 00:00:00 CST 2012
But notice what date -d "last Thursday" is:
$ TZ=CST date -d 'last Thursday CST'
Thu Mar 22 00:00:00 CST 2012
It's relative to the 'CST' timezone, which is an hour different from the
CDT timezone.
>
> If the date command where being consistent in following the consensus that
> "relative date operations add or subtract in multiples of 24 hours, without
> regards to daylight savings boundaries" then both of the above date commands
> would return Wed Feb 29 23:00:00 CST 2012.
Only if you start from the same point in time in both commands, which
you didn't.
--
Eric Blake address@hidden +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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