libc/time/tzset.3

         $NetBSD: tzset.3,v 1.9 1997/06/18 01:12:58 jtc Exp $
 TZSET 3
 NAME
tzset - initialize time conversion information
 SYNOPSIS
 void tzset()

 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 approximation to local wall clock time, as specified
by the
 tzfile (5)-format file
 localtime in the system time conversion 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 conversion 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 specification 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 information
directory.
The file must be in the format specified 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):
std\|offset[dst[offset][,rule]]

Where:

 15
 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 letters are explicitly allowed. Any characters
except a leading colon
 ( : ), digits, comma
 ( , ), minus
 ( - ), plus
 ( \(pl ), and ASCII NUL are allowed.

 offset Indicates the value one must add to the local time to arrive at
Coordinated 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) \(em if present \(em 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 indicated by an optional preceding
 `` \(pl '').
 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 happens. 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:

 10
 J n The Julian day
 n  "(1 \(<=" " n " "\(<= 365). Leap days are not counted; that is, in all years \(em including leap
years \(em 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.

 M m . 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.

 "" 15
The
 time has the same format as
 offset except that no leading sign
 (`` - '' or
 `` \(pl '') 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 conversion information directory are used, with the
standard and summer time offsets from UTC replaced by those specified 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
/etc/localtime local time zone file

/usr/share/zoneinfo time zone information directory

/usr/share/zoneinfo/posixrules used with POSIX-style TZ's

/usr/share/zoneinfo/GMT for UTC leap seconds
If
 /usr/share/zoneinfo/GMT is absent,
UTC leap seconds are loaded from
 /usr/share/zoneinfo/posixrules .  SEE ALSO
getenv(3),
ctime(3),
strftime(3),
time(3),
tzfile(5)
 @(#)newtzset.3 7.5