GNU bug report logs - #37961
Bug report of date commond

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: "zhangzhimin <at> mail.iap.ac.cn" <zhangzhimin <at> mail.iap.ac.cn>, 37961 <at> debbugs.gnu.org
Subject: bug#37961: Bug report of date commond
Date: Mon, 28 Oct 2019 11:52:11 -0700

On 10/28/19 12:34 AM, zhangzhimin <at> mail.iap.ac.cn wrote:
> ~>date  -d "1940-06-01" +"%Y-%m-%d"
> date: invalid date ‘1940-06-01’

Presumably your TZ setting is Asia/Shanghai, as I see the symptoms as 
follows:

$ TZ=Asia/Shanghai date  -d "1940-06-01" +"%Y-%m-%d"
date: invalid date ‘1940-06-01’

This is because there is no instant of time 1940-06-01 00:00:00 in 
Shanghai, as the the clock ticked over from 1940-05-30 23:59:59 to 
1940-06-01 01:00:00 due to a daylight-saving time transition.

For this particular case, you'll have better luck with:

$ date -d "1940-06-01 12:00" +"%Y-%m-%d"

but this sort of approach does not work in general, because 12:00 does 
not always exist either. In other words, the 'date' command is not 
suited for calendrical arithmetic in general, only for time arithmetic.

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