[tz] Version in zoneinfo files?

[John Hawkinson]

Paul Eggert <eggert at cs.ucla.edu> wrote on Fri, 10 Feb 2017
at 00:18:22 -0800 in <2c1949bd-fed5-a848-900b-4ac45b6deada at cs.ucla.edu>:

> On GNU/Linux a common tool for that is the 'file' command. For
> example, on Fedora 25:

I'm not quite sure what you're getting at, because I feel like
I could replace the word 'file' with  'ls -l' and
have your message convey the same information... :) Maybe -ld tho.

But yes, if we went with a prefixed string of '@(#)' and recorded
the original zone name in the file, it would be nice to have file(1)
display it as well; this is compatible with having the string displayed
by what(1), so would be great to do both. I am not a magic(5) expert,
but I believe the "search" operator lets that happen (and it would
only be invoked on files matching the existing 'TZif' magic string,
see magic/Magdir/timezone in the file source distribution).


In the other part of my thread, I fear Brian Inglis misunderstood my
intent. It was not to suggest that what(1) ought to be the only mechanism
to display this information (thus launching debates about how many
people have the tool installed, or whether it is obscure, etc., etc.); it
is instead to suggest adopting a mechanism compatible with it, so that
it works for many people today. That doesn't preclude a tz-specific 
tool (perhaps part of file(1) or standalone tool).

--jhawk at mit.edu
  John Hawkinson

> $ file /usr/share/zoneinfo/America/Los_Angeles
> /usr/share/zoneinfo/America/Los_Angeles: timezone data, version 2, 5
> gmt time flags, 5 std time flags, no leap seconds, 186 transition
> times, 5 abbreviation chars
> 
> Here the string "America/Los_Angeles" is already part of the output.
> Presumably the intended application for a change to the binary file
> format is when the binary file has been renamed or linked and
> someone wants to know the "originally-intended" or "canonical" name.
> tz follows the Unix tradition where files do not have canonical
> names - a design flaw to some, and a design feature to others.


$ ls -l /usr/share/zoneinfo/America/Los_Angeles
-rw-r--r-- 1 root root 2819 Dec  7 05:59 /usr/share/zoneinfo/America/Los_Angeles

Here the string "America/Los_Angeles" is already part of the output.
Presumably the intended application for a change to the binary file
format is when the binary file has been renamed or linked and
someone wants to know the "originally-intended" or "canonical" name.
tz follows the Unix tradition where files do not have canonical
names - a design flaw to some, and a design feature to others.