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Otherwise the tzload() (when called by gmtload()) fails to locate the UTC file and loads the posixrules.
339 lines
7.4 KiB
Groff
339 lines
7.4 KiB
Groff
.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Arthur Olson.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)tzset.3 8.2 (Berkeley) 11/17/93
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.\" $FreeBSD$
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.\"
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.Dd November 17, 1993
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.Dt TZSET 3
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.Os
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.Sh NAME
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.Nm tzset ,
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.Nm tzsetwall
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.Nd initialize time conversion information
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In time.h
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.Ft void
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.Fn tzset void
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.Ft void
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.Fn tzsetwall void
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.Sh DESCRIPTION
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The
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.Fn tzset
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function
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initializes time conversion information used by the library routine
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.Xr localtime 3 .
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The environment variable
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.Ev TZ
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specifies how this is done.
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.Pp
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If
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.Ev TZ
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does not appear in the environment, the best available approximation to
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local wall clock time, as specified by the
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.Xr tzfile 5 Ns -format
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file
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.Pa /etc/localtime
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is used.
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.Pp
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If
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.Ev TZ
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appears in the environment but its value is a null string, Coordinated
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Universal Time
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.Pq Tn UTC
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is used (without leap second correction).
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.Pp
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If
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.Ev TZ
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appears in the environment and its value begins with a colon
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.Pq Ql \&: ,
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the rest of its value is used as a pathname of a
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.Xr tzfile 5 Ns -format
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file from which to read the time conversion information.
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If the first character of the pathname is a slash
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.Pq Ql /
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it is used as
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an absolute pathname; otherwise, it is used as a pathname relative to
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the system time conversion information directory.
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.Pp
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If its value does not begin with a colon, it is first used as the pathname
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of a file (as described above) from which to read the time conversion
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information.
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If that file cannot be read, the value is then interpreted as a direct
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specification (the format is described below) of the time conversion
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information.
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.Pp
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If the
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.Ev TZ
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environment variable does not specify a
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.Xr tzfile 5 Ns -format
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file and cannot be interpreted as a direct specification,
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.Tn UTC
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is used.
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.Pp
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The
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.Fn tzsetwall
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function
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sets things up so that
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.Xr localtime 3
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returns the best available approximation of local wall clock time.
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.Sh SPECIFICATION FORMAT
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When
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.Ev TZ
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is used directly as a specification of the time conversion information,
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it must have the following syntax (spaces inserted for clarity):
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.Bd -ragged -offset indent
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.Em std offset
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.Bo
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.Em dst
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.Bq Em offset
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.Bq , Em rule
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.Bc
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.Ed
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.Pp
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Where:
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.Bl -tag -width std_and_dst -offset indent
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.It Em std No and Em dst
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Three or more bytes that are the designation for the standard
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.Pq Em std
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or summer
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.Pq Em dst
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time zone.
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Only
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.Em std
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is required; if
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.Em dst
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is missing, then summer time does not apply in this locale.
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Upper and lowercase letters are explicitly allowed.
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Any characters
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except a leading colon
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.Pq Ql \&: ,
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digits, comma
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.Pq Ql \&, ,
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minus
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.Pq Ql \- ,
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plus
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.Pq Ql + ,
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and
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.Tn ASCII
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.Dv NUL
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are allowed.
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.It Em offset
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Indicates the value one must add to the local time to arrive at
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Coordinated Universal Time.
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The
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.Em offset
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has the form:
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.Bd -ragged -offset indent
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.Sm off
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.Em hh Bo
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.Em : mm
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.Bq Em : ss
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.Bc
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.Sm on
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.Ed
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.Pp
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The minutes
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.Pq Em mm
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and seconds
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.Pq Em ss
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are optional.
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The hour
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.Pq Em hh
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is required and may be a single digit.
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The
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.Em offset
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following
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.Em std
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is required.
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If no
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.Em offset
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follows
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.Em dst ,
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summer time is assumed to be one hour ahead of standard time.
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One or
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more digits may be used; the value is always interpreted as a decimal
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number.
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The hour must be between zero and 24, and the minutes (and
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seconds) \(em if present \(em between zero and 59.
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If preceded by a
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.Pq Ql \-
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the time zone shall be east of the Prime Meridian; otherwise it shall be
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west (which may be indicated by an optional preceding
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.Pq Ql + ) .
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.It Em rule
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Indicates when to change to and back from summer time.
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The
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.Em rule
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has the form:
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.Bd -ragged -offset indent
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.Em date/time,date/time
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.Ed
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.Pp
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where the first
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.Em date
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describes when the change from standard to summer time occurs and the
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second
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.Em date
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describes when the change back happens.
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Each
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.Em time
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field describes when, in current local time, the change to the other
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time is made.
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.Pp
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The format of
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.Em date
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is one of the following:
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.Bl -tag -width "M.m.n.d"
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.It Sy J Em n
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The Julian day
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.Em n
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(1 \*(Le
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.Em n
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\*(Le 365).
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Leap days are not counted; that is, in all years \(em including leap
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years \(em February 28 is day 59 and March 1 is day 60.
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It is
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impossible to explicitly refer to the occasional February 29.
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.It Em n
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The zero-based Julian day
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(0 \*(Le
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.Em n
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\*(Le 365 ) .
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Leap days are counted, and it is possible to refer to February 29.
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.It Sy M Em m.n.d
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The
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.Em d Ns 'th
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day (0 \*(Le
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.Em d
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\*(Le 6)
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of week
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.Em n
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of month
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.Em m
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of the year
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(1 \*(Le
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.Em n
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\*(Le 5),
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(1 \*(Le
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.Em m
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\*(Le 12),
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where week 5 means
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.Do
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the last
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.Em d
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day in month
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.Em m
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.Dc
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which may occur in either the fourth or the fifth week).
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Week 1 is the
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first week in which the
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.Em d Ns 'th
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day occurs.
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Day zero is Sunday.
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.Pp
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The
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.Em time
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has the same format as
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.Em offset
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except that no leading sign
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.Pq Ql \-
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or
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.Pq Ql +
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is allowed.
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The default, if
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.Em time
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is not given, is
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.Sy 02:00:00 .
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.El
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.Pp
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If no
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.Em rule
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is present in the
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.Ev TZ
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specification, the rules specified
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by the
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.Xr tzfile 5 Ns -format
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file
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.Em posixrules
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in the system time conversion information directory are used, with the
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standard and summer time offsets from
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.Tn UTC
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replaced by those specified by
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the
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.Em offset
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values in
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.Ev TZ .
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.El
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.Pp
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For compatibility with System V Release 3.1, a semicolon
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.Pq Ql \&;
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may be used to separate the
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.Em rule
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from the rest of the specification.
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.Sh FILES
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.Bl -tag -width /usr/share/zoneinfo/posixrules -compact
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.It Pa /etc/localtime
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local time zone file
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.It Pa /usr/share/zoneinfo
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time zone directory
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.It Pa /usr/share/zoneinfo/posixrules
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rules for
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.Tn POSIX Ns -style
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.Tn TZ Ns 's
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.It Pa /usr/share/zoneinfo/Etc/GMT
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for
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.Tn UTC
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leap seconds
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.El
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.Pp
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If the file
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.Pa /usr/share/zoneinfo/UTC
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does not exist,
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.Tn UTC
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leap seconds are loaded from
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.Pa /usr/share/zoneinfo/posixrules .
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.Sh SEE ALSO
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.Xr date 1 ,
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.Xr gettimeofday 2 ,
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.Xr ctime 3 ,
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.Xr getenv 3 ,
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.Xr time 3 ,
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.Xr tzfile 5
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.Sh HISTORY
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The
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.Fn tzset
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and
|
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.Fn tzsetwall
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functions first appeared in
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.Bx 4.4 .
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