GNU bug report logs - #56524
doc: timezone offset conversion/info

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Message #8 received at 56524 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Karl Berry <karl <at> freefriends.org>
Cc: 56524 <at> debbugs.gnu.org, Gnulib bugs <bug-gnulib <at> gnu.org>
Subject: Re: bug#56524: doc: timezone offset conversion/info
Date: Tue, 12 Jul 2022 17:20:59 -0700

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

On 7/12/22 15:57, Karl Berry wrote:

> $ TZ=UTC-4 date -d 'TZ="UTC" 2022-07-24 15:00'

This doesn't mean what you want, because TZ=UTC-4 means "My time zone is 
abbreviated 'UTC', and it's four hours east of Greenwich" which is not a 
useful setting.

You're not the first person to run afoul of POSIX TZ strings, which are 
poorly designed. I installed the attached patch to Gnulib to give 
another example, which I hope clarifies things a bit. I'll cc this email 
to bug-gnulib since the problem is in Gnulib not Coreutils proper.

> If the offset syntax is documented anywhere, I couldn't find it. Sorry.

It's documented in the glibc manual, and this part of the Coreutils 
manual (actually, taken from Gnulib) has a cross-reference to that.

> BTW, in neither case did --debug clarify anything for me. In fact, it
> confused me more, because the output seemingly did not include anything
> about the offset at all, just reporting "UTC".

It'd be nice if --debug could diagnose invalid TZ settings. However, 
this would likely require glibc support along the lines of what's in 
tzcode and NetBSD (the tzalloc function).

[0001-parse-datetime-improve-doc-for-TZ-07-7-etc.patch (text/x-patch, attachment)]

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