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Subject:	RE: date function: daylight savings
Date:	Thu, 29 Sep 2005 22:49:05 -0600
Message-ID:	<3C46C4ED0F9B944690547357EB7F1C0F04A509@COFORTCOL2S304.agwest.one.usda.gov>
From:	"Pagano, Tom - Portland, OR" <tom DOT pagano AT por DOT usda DOT gov>
To:	"Eric Blake" <ebb9 AT byu DOT net>
Cc:	<cygwin AT cygwin DOT com>
X-MIME-Autoconverted:	from base64 to 8bit by delorie.com id j8U4nLZI009522

 
I see, so the issue is whether "1 day" is defined as 24 hours or the same hour/minute/second on the previous day. 
 
And this would apply to things on the front end of the season like 
 
$ date -d "2001-04-01 -1 day"
Sat Mar 31 00:00:00 PST 2001
$ date -d "2001-04-02 -2 day"
Fri Mar 30 23:00:00 PST 2001
 
as well. My workaround since I don't need the hours (just the year, month, day) might be to set the time to noon instead of midnight. 
 
$ date -d "12:00:00 2001-04-01 -1 day"
Sat Mar 31 11:00:00 PST 2001
$ date -d "12:00:00 2001-04-02 -2 day"
Sat Mar 31 11:00:00 PST 2001
 
Good info, lightning response, thanks. 
 
Tom
 

	-----Original Message----- 
	From: Eric Blake [mailto:ebb9 AT byu DOT net] 
	Sent: Thu 9/29/2005 9:49 PM 
	To: Pagano, Tom - Portland, OR 
	Cc: cygwin AT cygwin DOT com 
	Subject: Re: date function: how many days in october are there?
	
	

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	According to Pagano, Tom - Portland, OR on 9/29/2005 9:41 PM:
	> I've noticed that the date function does something strange trying to access October 31st in a statement like
	> 
	> $ date -d "1970-10-01 +1 month -1 day"
	> as opposed to something like
	> $ date -d "1970-11-01 -1 day"
	> which (I think??) should be functionally equivalent. The actual results of the 2nd are obviously preferrable to the 1st... but I do note something squirrly going on with the hours in both (daylight savings time?)
	
	Indeed it is daylight savings.  date has no cygwin-specific patches, but
	the brand new coreutils 5.90 has been released upstream that has some
	patches in date parsing.  Once I can get that packaged, you may want to
	rerun your tests - if the bug is still present at that time, then report
	it upstream.
	
	- --
	Life is short - so eat dessert first!
	
	Eric Blake             ebb9 AT byu DOT net
	volunteer cygwin coreutils maintainer
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