NAME
TZ - Time zone environment variable
SYNOPSIS
TZ=zone[-]offset[dst[offset][,start[/time],end[/time]]]
DESCRIPTION
The TZ environment variable tells functions such as the
ctime(3) family and programs like date what the time zone
and daylight saving rule is. The value of TZ has the POSIX
standardized form shown in the synopsis. This form speci-
fies the zone names, offsets from GMT, and daylight saving
changeover times for at least the current year.
zone A three or more letter name for the time zone in normal
(winter) time.
[-]offset
A signed time telling the offset of the time zone west-
wards from Greenwich. The time has the form
hh[:mm[:ss]] with a one of two digit hour, and optional
two digit minutes and seconds.
dst The name of the time zone when daylight saving is in
effect. It may be followed by an offset telling how
big the clock correction is other than the default of 1
hour.
start/time,end/time
Specifies the start and end of the daylight saving
period. The start and end fields indicate on what day
the changeover occurs. They must be in one of the fol-
lowing formats:
Jn The Julian day n (1 <= n <= 365) ignoring leap
days, i.e. there is no February 29.
n The zero-based Julian day (0 <= n <= 365). Leap
days are not ignored.
Mm.n.d
This indicates month m, the n-th occurrence of day
d (1 <= m <= 12, 1 <= n <= 5, 0 <= d <= 6, 0=Sun-
day). The 5-th occurrence means the last
occurrence of that day in a month. So M4.1.0 is
the first Sunday in April, M9.5.0 is the last Sun-
day in September.
The time field indicates the time the changeover occurs
on the given day.
EXAMPLES
Greenwich Mean Time:
TZ=GMT0
Central European Time, 1 hour east from Greenwich, daylight
saving starts on the last Sunday in March at 2 AM and ends
on the last Sunday in October at 3 AM:
TZ='CET-1CEST,M3.5.0/2,M10.5.0/3'
British time, daylight saving starts and ends at the same
moment as CET, but in an earlier time zone:
TZ=GMT0BST,M3.5.0/1,M10.5.0/2
The eastern european time zones also have the changeovers at
the same absolute time as British time and CET.
U.S. Eastern Standard Time, 5 hours west from Greenwich,
daylight saving starts on the first Sunday in April at 2 AM
and ends on the last Sunday in October at 2 AM:
TZ=EST5EDT,M4.1.0/2,M10.5.0/2
It shouldn't surprise you that daylight saving in New Zea-
land is observed in the months opposite from the previous
examples. It starts on the first Sunday in October at 2 AM
and ends on the third Sunday in March at 3 AM:
TZ=NZST-12NZDT,M10.1.0/2,M3.3.0/3
SEE ALSO
readclock(8), date(1).
BUGS
You may have noticed that many fields are optional. Do no
omit them, because the defaults are bogus. If you need day-
light saving then fully specify the changeovers.
West is negative, east is positive, ask any sailor.
Next year's time zone and daylight saving time are deter-
mined by politicians.
AUTHOR
Kees J. Bot (kjb@cs.vu.nl)