newtzset

NAME

       tzset - initialize time conversion information

SYNOPSIS

       void tzset()

       cc ... -lz

DESCRIPTION

       Tzset uses the value of the environment variable TZ to set
       time conversion information used by localtime.  If TZ does
       not appear in the environment, the best available approxi-
       mation to local wall  clock  time,  as  specified  by  the
       tzfile(5)-format file localtime in the system time conver-
       sion information directory, is used by localtime.   If  TZ
       appears in the environment but its value is a null string,
       Coordinated Universal Time (UTC)  is  used  (without  leap
       second  correction).  If TZ appears in the environment and
       its value is not a null string:

              if the value begins with a colon, it is used  as  a
              pathname of a file from which to read the time con-
              version information;

              if the value does not begin with  a  colon,  it  is
              first  used as the pathname of a file from which to
              read the time conversion information, and, if  that
              file cannot be read, is used directly as a specifi-
              cation of the time conversion information.

       When TZ is used as a pathname, if it begins with a  slash,
       it  is used as an absolute pathname; otherwise, it is used
       as a pathname relative to a system time conversion  infor-
       mation  directory.   The file must be in the format speci-
       fied in tzfile(5).

       When TZ is used directly as a specification  of  the  time
       conversion  information, it must have the following syntax
       (spaces inserted for clarity):

              stdoffset[dst[offset][,rule]]

       Where:

              std and dst    Three or more  bytes  that  are  the
                             designation  for  the standard (std)
                             or summer (dst) time zone.  Only std
                             is required; if dst is missing, then
                             summer time does not apply  in  this
                             locale.   Upper-  and lowercase let-
                             ters are  explicitly  allowed.   Any
                             characters  except  a  leading colon
                             (:), digits, comma (,),  minus  (-),
                             plus (+), and ASCII NUL are allowed.

              offset         Indicates the value one must add  to
                             the  local time to arrive at Coordi-
                             nated Universal  Time.   The  offset
                             has the form:

                                    hh[:mm[:ss]]

                             The  minutes  (mm)  and seconds (ss)
                             are  optional.   The  hour  (hh)  is
                             required  and may be a single digit.
                             The   offset   following   std    is
                             required.  If no offset follows dst,
                             summer time is  assumed  to  be  one
                             hour ahead of standard time.  One or
                             more digits may be used;  the  value
                             is  always  interpreted as a decimal
                             number.  The hour  must  be  between
                             zero  and  24,  and the minutes (and
                             seconds) -- if  present  --  between
                             zero  and  59.   If  preceded  by  a
                             ``-'', the time zone shall  be  east
                             of  the Prime Meridian; otherwise it
                             shall be west (which  may  be  indi-
                             cated   by   an  optional  preceding
                             ``+'').

              rule           Indicates when to change to and back
                             from  summer time.  The rule has the
                             form:

                                    date/time,date/time

                             where the first date describes  when
                             the  change  from standard to summer
                             time  occurs  and  the  second  date
                             describes  when the change back hap-
                             pens.   Each  time  field  describes
                             when,  in  current  local  time, the
                             change to the other time is made.

                             The format of date  is  one  of  the
                             following:

                             Jn        The     Julian    day    n
                                       (1 <= n <= 365).      Leap
                                       days are not counted; that
                                       is,  in   all   years   --
                                       including  leap  years  --
                                       February 28 is day 59  and
                                       March  1 is day 60.  It is
                                       impossible  to  explicitly
                                       refer  to  the  occasional
                                       February 29.

                             n         The zero-based Julian  day
                                       (0 <= n <= 365).      Leap
                                       days are counted,  and  it
                                       is  possible  to  refer to
                                       February 29.

                             Mm.n.d    The d'th day (0 <= d <= 6)
                                       of  week  n  of month m of
                                       the   year   (1 <= n <= 5,
                                       1 <= m <= 12, where week 5
                                       means ``the last d day  in
                                       month  m'' which may occur
                                       in either  the  fourth  or
                                       the  fifth  week).  Week 1
                                       is the first week in which
                                       the  d'th day occurs.  Day
                                       zero is Sunday.

                             The time has the same format as off-
                             set  except  that  no  leading  sign
                             (``-'' or ``+'')  is  allowed.   The
                             default,  if  time  is not given, is
                             02:00:00.

       If no rule is present in TZ, the rules  specified  by  the
       tzfile(5)-format  file  posixrules in the system time con-
       version information directory are used, with the  standard
       and  summer time offsets from UTC replaced by those speci-
       fied by the offset values in TZ.

       For compatibility with System V Release 3.1,  a  semicolon
       (;)  may be used to separate the rule from the rest of the
       specification.

       If  the  TZ  environment  variable  does  not  specify   a
       tzfile(5)-format  and  cannot  be  interpreted as a direct
       specification, UTC is used.

FILES

       /usr/local/etc/zoneinfo             time zone  information
       directory
       /usr/local/etc/zoneinfo/localtime   local time zone file
       /usr/local/etc/zoneinfo/posixrules  used  with POSIX-style
       TZ's
       /usr/local/etc/zoneinfo/GMT         for UTC leap seconds

       If /usr/local/etc/zoneinfo/GMT is absent, UTC leap seconds
       are loaded from /usr/local/etc/zoneinfo/posixrules.

SEE ALSO

       getenv(3), newctime(3), time(2), tzfile(5)