Standard for timezone handling with TZ

[Paul Eggert]

In comp.unix.solaris Casper H.S. Dik writes:

> SunOS 4:
> % env TZ=GMT-4 date			GMT-4 is a timezone file (Olson)
> Thu Feb 10 04:29:42 GMT-0400 1994
> % env TZ=GMT-04 date			But use POSIX rules here
> Thu Feb 10 12:32:21 GMT 1994

That's a bug in the Olson rules; they aren't compatible with Posix
1003.1-1990.  Thanks for pointing it out.  Here's a conservative patch
to Olson's latest version which renames `GMT-4' to `GMT-0400' to avoid
the bug.

Another possibility is simply to remove the GMT[-+]* rules, since their
sign is the opposite of the sign in the Posix TZ string, and this is confusing.

*** etcetera	1992/04/23 17:34:35	7.1
--- etcetera	1994/02/10 19:49:45	7.1.1.1
***************
*** 6,55 ****
  
  Zone	GMT		0	-	GMT
  
! Zone	GMT-12		-12	-	GMT-1200
! Zone	GMT-11		-11	-	GMT-1100
! Zone	GMT-10		-10	-	GMT-1000
! Zone	GMT-9		-9	-	GMT-0900
! Zone	GMT-8		-8	-	GMT-0800
! Zone	GMT-7		-7	-	GMT-0700
! Zone	GMT-6		-6	-	GMT-0600
! Zone	GMT-5		-5	-	GMT-0500
! Zone	GMT-4		-4	-	GMT-0400
! Zone	GMT-3		-3	-	GMT-0300
! Zone	GMT-2		-2	-	GMT-0200
! Zone	GMT-1		-1	-	GMT-0100
! Zone	GMT+1		1	-	GMT+0100
! Zone	GMT+2		2	-	GMT+0200
! Zone	GMT+3		3	-	GMT+0300
! Zone	GMT+4		4	-	GMT+0400
! Zone	GMT+5		5	-	GMT+0500
! Zone	GMT+6		6	-	GMT+0600
! Zone	GMT+7		7	-	GMT+0700
! Zone	GMT+8		8	-	GMT+0800
! Zone	GMT+9		9	-	GMT+0900
! Zone	GMT+10		10	-	GMT+1000
! Zone	GMT+11		11	-	GMT+1100
! Zone	GMT+12		12	-	GMT+1200
! Zone	GMT+13		13	-	GMT+1300	# GMT+12 with DST
  
  Link	GMT		UTC
  Link	GMT		UCT
  Link	GMT		Universal
  Link	GMT		Greenwich
  Link	GMT		Zulu
! Link	GMT		GMT-0
! Link	GMT		GMT+0
! Link	GMT		GMT0
! Link	GMT+1		GMT1
! Link	GMT+2		GMT2
! Link	GMT+3		GMT3
! Link	GMT+4		GMT4
! Link	GMT+5		GMT5
! Link	GMT+6		GMT6
! Link	GMT+7		GMT7
! Link	GMT+8		GMT8
! Link	GMT+9		GMT9
! Link	GMT+10		GMT10
! Link	GMT+11		GMT11
! Link	GMT+12		GMT12
! Link	GMT+13		GMT13
--- 6,41 ----
  
  Zone	GMT		0	-	GMT
  
! Zone	GMT-1200	-12	-	GMT-1200
! Zone	GMT-1100	-11	-	GMT-1100
! Zone	GMT-1000	-10	-	GMT-1000
! Zone	GMT-0900	-9	-	GMT-0900
! Zone	GMT-0800	-8	-	GMT-0800
! Zone	GMT-0700	-7	-	GMT-0700
! Zone	GMT-0600	-6	-	GMT-0600
! Zone	GMT-0500	-5	-	GMT-0500
! Zone	GMT-0400	-4	-	GMT-0400
! Zone	GMT-0300	-3	-	GMT-0300
! Zone	GMT-0200	-2	-	GMT-0200
! Zone	GMT-0100	-1	-	GMT-0100
! Zone	GMT+0100	1	-	GMT+0100
! Zone	GMT+0200	2	-	GMT+0200
! Zone	GMT+0300	3	-	GMT+0300
! Zone	GMT+0400	4	-	GMT+0400
! Zone	GMT+0500	5	-	GMT+0500
! Zone	GMT+0600	6	-	GMT+0600
! Zone	GMT+0700	7	-	GMT+0700
! Zone	GMT+0800	8	-	GMT+0800
! Zone	GMT+0900	9	-	GMT+0900
! Zone	GMT+1000	10	-	GMT+1000
! Zone	GMT+1100	11	-	GMT+1100
! Zone	GMT+1200	12	-	GMT+1200
! Zone	GMT+1300	13	-	GMT+1300	# GMT+12 with DST
  
  Link	GMT		UTC
  Link	GMT		UCT
  Link	GMT		Universal
  Link	GMT		Greenwich
  Link	GMT		Zulu
! Link	GMT		GMT-0000
! Link	GMT		GMT+0000