TZ(5)

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 specifies 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  westwards  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 following 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=Sunday).  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 Sunday 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 Zealand 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 daylight 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  determined  by
     politicians.

AUTHOR
     Kees J. Bot (kjb@cs.vu.nl)