Re: _time_zone gives me candidates other than timezones

[Aaron Schrab <aaron@schrab.com>]

At 16:22 -0700 29 Mar 2022, Bart Schaefer <schaefer@brasslantern.com> wrote:
>On Thu, Mar 24, 2022 at 12:28 PM Jordan Russell
><jordan.likes.curry@gmail.com> wrote:
>>
>> I would like _time_zone to exclude these filenames that are not
>> timezones [...]
>>
>> If I modify it to just exclude those files that begin with a lowercase
>> letter then it gives me only proper timezone names.
>
>That excludes the directories "posix" and "right" on my system (I have
>no idea what the latter one means).

Quoting from https://www.ucolick.org/~sla/leapsecs/right+gps.html:

    The "right" files in the tz (zoneinfo) database have a subtle 
    difference from the POSIX standard. POSIX requires that the system 
    clock value of time_t represent the number of non-leap seconds since 
    1970-01-01. This is the same as requiring POSIX seconds to be mean 
    solar seconds of UT, not the atomic seconds that UTC has counted 
    since 1972-01-01.

   The "right" zoneinfo files assert that the system clock value of 
   time_t represent the actual number of seconds in the internationally 
   approved broadcast time scale since 1970-01-01. As a result the value 
   of time_t which is expected by the "right" zoneinfo files is greater 
   than the value of time_t specified by POSIX. The difference in the 
   values of time_t is the number of leap seconds which have been 
   inserted into the internationally approved broadcast time scale. As of 
   year 2011 the difference is 24 seconds. 

I'm a bit more puzzled about why the separate `posix` directory exists. 
At least for my local time zone it doesn't seem to matter if I use that 
or leave it out; while using the `right` one definitely makes a 
difference:

date; TZ=right/America/New_York date; TZ=posix/America/New_York date
2022-03-29T20:07:47 EDT
2022-03-29T20:07:20 EDT
2022-03-29T20:07:47 EDT

>Is everyone OK with that?

While I don't think I've ever really needed to use zoneinfo entries from 
those directories, I'd certainly prefer they be offered for completion.