Re: bug-coreutils date command

[Philip Rowlands]

On Mon, 3 Dec 2007, Richard Narum wrote:

> I'm not sure if you would call this a bug or not but I'm wondering why 
> the GNU date command doesn't have the correct time adjustment for 
> daylight savings from years past on its output when using an input 
> date string to generate its output.

> I am currently running GNU coreutils 6.9 with Cygwin on Windows XP 
> version "CYGWIN_NT-5.1 1.5.24(0.156/4/2) 2007-01-31 10:57".

What version of the tzcode package do you have, if any? 
/var/log/setup.log contains this info on my Cygwin installation - I 
don't know the "proper" way to check, which the installer uses.

> The following commands shows dates when CST switches to CDT and back.
>
> $ export TZ=CST6CDT

What does this mean? Specifically, without giving the full syntax (e.g. 
"EST5EDT4,116/2:00:00,298/2:00:00") how is the C library to know what 
rules are passed by Congress regarding the DST switchover date?

The usual way is to have a large collection of files giving the 
historical date patterns and gmt offsets. If your system has an old 
(pre-2005?) version of these files, or none at all, date and the 
localtime(3) function it calls can't help.

> Could someone shed some light on why maybe additional rules are not 
> applied?

I remember being told once that the "CST8CDT" pattern was now broken by 
the Energy Policy Act changes, but I can't find a reference. The best 
thing to do is avoid that syntax and use the location-based files 
instead; e.g. "America/Chicago" for Central Standard/Daylight Time.


Cheers,
Phil