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.. > > [root@schaefer-test ~]# 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.. > > [root@schaefer-test ~]# 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 ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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