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|ID||Category||Severity||Type||Date Submitted||Last Update|
|0001252||[1003.1(2016)/Issue7+TC2] Base Definitions and Headers||Objection||Enhancement Request||2019-06-02 21:37||2019-06-02 22:12|
|Section||8.3 Other Environment Variables - TZ|
|Final Accepted Text|
|Summary||0001252: Extend TZ to allow times outside 00-24 range, permanent DST|
The tzdb project is a widely-used extension to POSIX, and represents the history of a time zone partly via a final POSIX TZ string representing future timestamps. For example, on my Ubuntu system, the TZif file /usr/share/zoneinfo/America/Los_Angeles ends in the line 'PST8PDT,M3.2.0,M11.1.0', which means that one can use TZ='PST8PDT,M3.2.0,M11.1.0' to predict future timestamps. The tzdb project is widely supported and the format of its TZif files has recently been standardized by Internet RFC 8536 <https://tools.ietf.org/html/rfc8536>. [^]
While coauthoring RFC 8536 I noticed that tzdb's use of TZ strings relies on two minor extensions to POSIX's specification of TZ. These extensions were already supported by at least the reference tzcode implementation and by NetBSD, and so are good candidates for standardization by POSIX. Adding them to POSIX will bless the commonly used practice of taking the last line of a TZif file and using it as a TZ string on small platforms that lack room to store the TZif files.
The two minor extensions are specified in Internet RFC 8536 section 3.3.1 "TZ String Extensions" <https://tools.ietf.org/html/rfc8536#page-13>, [^] and the proposed action is to add these to POSIX.
This proposal would address Austin Group issue 0000661 "grammar of TZ variable is insufficient for describing Israel Daylight-saving time", as TZ='IST-2IDT,M3.4.4/26,M10.5.0' represents current rules for Israel, with the '/26' exercising the proposed extension. It would also let POSIX TZ strings represent the current daylight-saving scheme for Godthab, via TZ='<-03>3<-02>,M3.5.0/-2,M10.5.0/-1' where the '/-2' and '/-1' exercise the proposed extension.
In the description of the TZ rule, change from:
The /time/ has the same format as /offset/ except that no leading sign ('-' or '+') is allowed.
The /time/ has the same format as /offset/ except that the hour can range from zero to 167. If preceded by a '-', the /time/ shall count backwards before midnight. For example, '47:30' stands for 23:30 the next day, and '-3:30' stands for 20:30 the previous day.
At the end of the description of the TZ rule, add:
Alternative time is in effect all year if it starts January 1 at 00:00 and ends December 31 at 24:00 plus the difference between daylight saving and standard time, leaving no room for standard time in the calendar. For example, TZ='EST5EDT,0/0,J365/25' represents a time zone that observes alternative time all year, being 4 hours west of UTC with abbreviation "EDT".
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|2019-06-02 21:37||eggert||New Issue|
|2019-06-02 21:37||eggert||Name||=> Paul Eggert|
|2019-06-02 21:37||eggert||Organization||=> UCLA|
|2019-06-02 21:37||eggert||Section||=> 8.3 Other Environment Variables - TZ|
|2019-06-02 21:37||eggert||Page Number||=> unknown; don't have PDF|
|2019-06-02 21:37||eggert||Line Number||=> unknown; don't have PDF|
|2019-06-02 21:56||Don Cragun||Relationship added||related to 0000661|
|2019-06-02 22:12||Don Cragun||Page Number||unknown; don't have PDF => 180|
|2019-06-02 22:12||Don Cragun||Line Number||unknown; don't have PDF => 5945-5946|
|2019-06-02 22:12||Don Cragun||Interp Status||=> ---|
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