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