[R] POSIX time zone codes

[Prof Brian Ripley]

On Wed, 8 Mar 2006, Don MacQueen wrote:

> I would have suggested "US/Central", by analogy with "US/Pacific"
> which I use on my unix-like Mac OS X 10.3.9 system. I don't know what
> might be "common knowledge" in UNIX circles, but here's a bit of
> information from my system.
>
> It has a directory named /usr/share/zoneinfo.
>
> zoneinfo[166]% pwd
> /usr/share/zoneinfo
>
> zoneinfo[167]% ls | grep DT
> CST6CDT
> EST5EDT
> MST7MDT
> PST8PDT
>
> There are files named GMT, UTC, GB, and a number of others.
>
> There are numerous subdirectories, including for example, "Asia",
> "Australia", "Europe", "US".
>
> zoneinfo[168]% cd US
> US[169]% ls
> ./              Aleutian        East-Indiana    Indiana-Starke  Pacific
> ../             Arizona         Eastern         Michigan        Pacific-New
> Alaska          Central         Hawaii          Mountain        Samoa
>
> This suggests to me that valid values for the tz argument are
> relative paths to files /usr/share/zoneinfo, but I don't know that
> for a fact.

That is documented as _one_ of the allowed forms on MacOS X, and 'man 
tzset' will show you others (I looked at online version for your OS). 
Strictly, that form should be preceded by a colon, that is ':US/Central'. 
But the information is only in 'man tzset' on some systems.

According to http://www.twinsun.com/tz/tz-link.htm this is the case on 
most Unix-alikes, although the base path differs considerably.

However, :US/Central is not valid on Windows, and in fact as far as I know 
Windows only allows you to set (via TZ) timezones with no DST or the US 
rules for DST.  The Control Panel knows some other sets of rules.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595