GNU bug report logs - #8648
bug in date?

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: "Turner, Neil" <tnturner <at> amazon.com>
To: "bug-coreutils <at> gnu.org" <bug-coreutils <at> gnu.org>
Subject: bug in date?
Date: Tue, 10 May 2011 16:36:38 -0700

[Message part 1 (text/plain, inline)]

Maybe found a bug in date...  the following command:

$ date --date="yesterday 00:00 +1 day"
Mon May  9 16:59:00 PDT 2011

The date as I type this is May 10th... so I was expecting the output to be:
Tues May  10 00:00:00 PDT 2011

Thanks,

Neil

[Message part 2 (text/html, inline)]

Message #8 received at 8648 <at> debbugs.gnu.org (full text, mbox):

From: Ondrej Vasik <ovasik <at> redhat.com>
To: "Turner, Neil" <tnturner <at> amazon.com>
Cc: 8648 <at> debbugs.gnu.org
Subject: Re: bug#8648: bug in date?
Date: Wed, 11 May 2011 06:31:56 +0200

On Tue, 2011-05-10 at 16:36 -0700, Turner, Neil wrote:
> Maybe found a bug in date...  the following command:
> 
> $ date --date="yesterday 00:00 +1 day"
> Mon May  9 16:59:00 PDT 2011
> 
> The date as I type this is May 10th... so I was expecting the output to be:
> Tues May  10 00:00:00 PDT 2011

First of all, please always report the version of coreutils where you
experience the unexpected behaviour.

However - it is a tricky thing - you are human, you know what you have
meant by +1 ... but flex getdate parser is not a human - and it simply
parses the date format. In this case date format expects +1 is timezone
(and because I see the offset of 1 minute, I think you have quite old
version of coreutils). +1 is then implicit for the relative time offset
(you may consider date --date="yesterday 00:00 +3 day" to be even more
"buggy"). Not too much to do, date parser is very fragile and you will
always have this kind of disambiguations there. So there is only one
hint, make the format as complete as possible (date time timezone
offset)...

With `date --date="yesterday 00:00 PDT +1 day"` you should get the date
you expected.

Greetings,
         Ondrej Vasik

Message #11 received at 8648 <at> debbugs.gnu.org (full text, mbox):

From: Jim Meyering <jim <at> meyering.net>
To: "Turner Neil" <tnturner <at> amazon.com>
Cc: 8648 <at> debbugs.gnu.org, ovasik <at> redhat.com
Subject: Re: bug#8648: bug in date?
Date: Wed, 11 May 2011 08:00:33 +0200

tag 8648 + notabug
close 8648
thanks

Ondrej Vasik wrote:
> On Tue, 2011-05-10 at 16:36 -0700, Turner, Neil wrote:
>> Maybe found a bug in date...  the following command:
>>
>> $ date --date="yesterday 00:00 +1 day"
>> Mon May  9 16:59:00 PDT 2011
>>
>> The date as I type this is May 10th... so I was expecting the output to be:
>> Tues May  10 00:00:00 PDT 2011
>
> First of all, please always report the version of coreutils where you
> experience the unexpected behaviour.
>
> However - it is a tricky thing - you are human, you know what you have
> meant by +1 ... but flex getdate parser is not a human - and it simply
> parses the date format. In this case date format expects +1 is timezone
> (and because I see the offset of 1 minute, I think you have quite old
> version of coreutils). +1 is then implicit for the relative time offset
> (you may consider date --date="yesterday 00:00 +3 day" to be even more
> "buggy"). Not too much to do, date parser is very fragile and you will
> always have this kind of disambiguations there. So there is only one
> hint, make the format as complete as possible (date time timezone
> offset)...
>
> With `date --date="yesterday 00:00 PDT +1 day"` you should get the date
> you expected.

Thanks for the report, Neil, and for replying, Ondřej.

Neil, if you run "info date example", you'll see pretty many examples.
There are some here, too:
http://www.gnu.org/software/coreutils/faq/coreutils-faq.html#The-date-command-is-not-working-right_002e

BTW, simply removing the "+" should make date do what you
want most of the time:

  $ date --date="yesterday 00:00 1 day"

However, that may well fail around DST changes (as explained
in detail via that FAQ), so you should use noon rather than midnight:

  $ date --date="yesterday 12:00 1 day"

P.S. I've closed this ticket but you're welcome to continue discussing
and even to reopen it if I've missed something.

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