GNU bug report logs - #26293
GNU date program

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

From: Dean Gibson AE7Q <wa7dem.stuff <at> ae7q.com>
To: bug-coreutils <at> gnu.org
Subject: GNU date program
Date: Tue, 28 Mar 2017 19:26:06 -0700

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

Consider: "date -d '2017-03-28 17:12:34 + 3 hours'"

In "date (coreutils) 5.2.1  (March 2004)" it gives "Tue Mar 28 20:12:34 
PDT 2017".

In "GNU coreutils 8.22 February 2016)" it gives "Tue Mar 28 08:12:34 PDT 
2017".

Both servers use /etc/localtime -> /usr/share/zoneinfo/PST8PDT

If I insert "PDT" in the original string after the time, it works on 
both servers.  Unfortunately, since the servers run in an area that is 
subject to daylight savings time part of the year, hard coding the 'PDT' 
zone in the script it was in, is not appropriate.

On both servers, "date -d '2017-03-28 17:12:34 3 hours ago'" works. Is 
there a "3 hours ahead"-type phrase???

I have settled on "... 21 hours ago tomorrow", which works on both servers.

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

Message #8 received at 26293 <at> debbugs.gnu.org (full text, mbox):

From: Assaf Gordon <assafgordon <at> gmail.com>
To: Dean Gibson AE7Q <wa7dem.stuff <at> ae7q.com>
Cc: 26293 <at> debbugs.gnu.org
Subject: Re: bug#26293: GNU date program
Date: Wed, 29 Mar 2017 10:18:33 -0400

tags 26293 notabug
close 26293
stop

Hello,

> On Mar 28, 2017, at 22:26, Dean Gibson AE7Q <wa7dem.stuff <at> ae7q.com> wrote:
> 
> Consider: "date -d '2017-03-28 17:12:34 + 3 hours'"

Due to the way date strings are parsed, the "+3" part is used as the input time zone (+03:00) and then the "hours" part is taken as adding one hour.

> If I insert "PDT" in the original string after the time, it works on both servers.

Yes, once the parser sees an explicit timezone (PDT), it deduces the rest is a relative time ("+3 hours").


> On both servers, "date -d '2017-03-28 17:12:34 3 hours ago'" works. Is there a "3 hours ahead"-type phrase???

Yes, simply writing "3 hours" means "3 hours ahead".

Additionally,
The 'date' command in coreutils 8.27 has a new "--debug" option that displays
details about the parsed string, helping in diagnosing such issues.

Compare the following examples:

"+3" treated as timezone:

  $ date --debug -d '2017-03-28 17:12:34 + 3 hours'
  date: parsed date part: (Y-M-D) 2017-03-28
  date: parsed time part: 17:12:34 TZ=+03:00
  date: parsed relative part: +1 hour(s)
  date: input timezone: +03:00 (set from parsed date/time string)
  ...

Adding "PDT" works, but not the desired solution:

  $ date --debug -d '2017-03-28 17:12:34 PDT + 3 hours'
  date: parsed date part: (Y-M-D) 2017-03-28
  date: parsed time part: 17:12:34
  date: parsed zone part: TZ=-07:00
  date: parsed relative part: +3 hour(s)
  date: input timezone: -07:00 (set from parsed date/time string)
  ...

"3 hours" works:

  $ date --debug -d '2017-03-28 17:12:34 3 hours'
  date: parsed date part: (Y-M-D) 2017-03-28
  date: parsed time part: 17:12:34
  date: parsed relative part: +3 hour(s)
  ...


I'm marking this as "not-a-bug", but the discussion can continue by
replying to this thread.

regards,
 - assaf

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