Re: 780 files in /usr/share/zoneinfo/
On Tue, Nov 24, 2020 at 04:45:53PM +0000, Curt wrote:
> I have a problem:
>
> curty@einstein:~$ TZ=EST date
> Tue Nov 24 11:43:42 EST 2020
> curty@einstein:~$ TZ=PST date
> Tue Nov 24 16:43:54 PST 2020
As I said, figuring out the valid TZ strings for a given location on
our planet is a challenge. Unfortunately, the ... fine people ... who
devised the standards for this sort of thing thought it would be really
super clever to treat ALL unknown TZ strings as if they were "UTC0".
unicorn:~$ date -u ; TZ=UTC0 date ; TZ=Imaginary/Neverland date
Tue Nov 24 17:54:28 UTC 2020
Tue Nov 24 17:54:28 UTC 2020
Tue Nov 24 17:54:28 Imaginary 2020
TZ=PST is yet another unknown TZ string, so it's treated as "UTC0", or
the Coordinated Universal Time zone, and you don't even get a WARNING
that this is the case. It just silently gives you a wrong answer.
I've been personally bitten by this, and it sucks. So much.
unicorn:~$ TZ=PST date ; TZ=PST8PDT date ; TZ=America/Los_Angeles date
Tue Nov 24 17:56:16 PST 2020
Tue Nov 24 09:56:16 PST 2020
Tue Nov 24 09:56:16 PST 2020
To add insult to injury, the string that date(1) gives you as OUTPUT
(in this case, "PST") is not accepted by the very same program as INPUT.
In fact, I don't know of any way to get date(1) to give an output string
that you can use as a valid TZ input string. You have to discover these
values yourself, using out-of-band means.
One of the ways to generate a valid TZ name, if your target happens to
be in the United States, is to construct one of the old school Unix time
zone names:
EST5EDT
CST6CDT
MST7MDT
PST8PDT
If you can remember "Eastern Central Mountain Pacific", and if you can
remember the numeric offset for any single one of them, then you can
derive the full set.
Another set of TZ labels that works for the USA is the transitional
set that was popular 10-20 years ago:
US/Eastern
US/Central
US/Mountain
US/Pacific
Those are even easier to derive than the "EST5EDT" style ones, albeit
slightly more characters to type.
Outside of the USA, you'll probably need to go with the "nearest big
city" names that are the current vogue. The best way to use those is
probably "ls /usr/share/zoneinfo", choose your continent, and then
(for example) "ls /usr/share/zoneinfo/Asia". Then pick a city from
the resulting set, and pray.
If there's a better way, I don't know it.
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