b6cbf7203b
This patch imports the unmodified current version of NetBSD libc. The NetBSD includes are in /nbsd_include, while the libc code itself is split between lib/nbsd_libc and common/lib/libc.
269 lines
5.5 KiB
Groff
269 lines
5.5 KiB
Groff
.\" $NetBSD: tzset.3,v 1.25 2010/12/17 01:29:45 wiz Exp $
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.Dd April 1, 2001
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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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.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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.Sh DESCRIPTION
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The
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.Fn tzset
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function uses the value of the environment variable
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.Ev TZ
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to set time conversion information used by
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.Xr localtime 3 .
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If
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.Ev TZ
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does not appear in the environment,
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the best available approximation to local wall clock time, as
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specified by the
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.Xr tzfile 5
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format file
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.Pa /etc/localtime
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is used by
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.Xr localtime 3 .
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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,
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Coordinated Universal Time (UTC) is used (without leap second
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correction).
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If
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.Ev TZ
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appears in the environment and its value is not a null string:
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.Bl -dash
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.It
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if the value begins with a colon, it is used as a pathname of a file
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from which to read the time conversion information;
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.It
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if the value does not begin with a colon, it is first used as the
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pathname of a file from which to read the time conversion information,
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and, if that file cannot be read, is used directly as a specification
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of the time conversion information.
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.El
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.Pp
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When
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.Ev TZ
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is used as a pathname, if it begins with a slash, it is used as an
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absolute pathname; otherwise, it is used as a pathname relative to
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.Pa /usr/share/zoneinfo .
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The file must be in the format specified in
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.Xr tzfile 5 .
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.Pp
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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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.Sm off
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.Bd -literal -offset indent
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.Cm std Cm offset Oo
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.Cm dst Oo
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.Cm offset Oc Oo
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.No , Cm rule Oc Oc
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.Ed
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.Sm on
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.Pp
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where:
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.Bl -tag -width "std and dst" -compact
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.It Cm std No and Cm dst
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Three or more bytes that are the designation for the standard
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.Cm ( std )
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or summer
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.Cm ( dst )
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time zone.
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Only
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.Cm std
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is required; if
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.Cm 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 except a leading colon (:), digits, comma (,), minus (-),
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plus (+), and ASCII NUL are allowed.
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.It Cm 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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.Cm offset
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has the form:
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.Sm off
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.Bd -literal -offset indent
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.Cm hh Oo
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.Cm :mm Oo
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.Cm :ss Oc Oc
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.Ed
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.Sm on
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.Pp
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The minutes
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.Cm ( mm )
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and seconds
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.Cm ( ss )
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are optional.
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The hour
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.Cm ( hh )
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is required and may be a single digit.
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The
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.Cm offset
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following
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.Cm std
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is required.
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If no
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.Cm offset
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follows
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.Cm dst ,
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summer time is assumed to be one hour ahead of standard time.
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One or more digits may be used; the value is always interpreted as a
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decimal 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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.Dq -
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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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.Dq + ) .
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.It Cm rule
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Indicates when to change to and back from summer time.
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The
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.Cm rule
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has the form:
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.Sm off
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.Bd -literal -offset indent
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.Xo
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.Cm date No /
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.Cm time No ,
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.Cm date No /
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.Cm time
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.Xc
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.Ed
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.Sm on
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.Pp
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where the first
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.Cm 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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.Cm date
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describes when the change back happens.
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Each
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.Cm 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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The format of
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.Fa date
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is one of the following:
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.Bl -tag -width "The Julian day" -compact
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.It Cm J Ns Ar n
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The Julian day
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.Ar n
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(1 \*[Le]
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.Ar 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 impossible to explicitly refer to the occasional February 29.
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.It Ar n
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The zero-based Julian day (0\ \*[Le]
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.Ar n
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\*[Le]\ 365).
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Leap days are counted, and it is possible to refer to
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February 29.
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.Sm off
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.It Cm M Ns Ar m No . Ar n No . Ar d
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.Sm on
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The
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.Ar d Ns 'th
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day
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(0 \*[Le]
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.Ar d
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\*[Le]\ 6) of week
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.Ar n
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of month
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.Ar m
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of the year
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(1 \*[Le]
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.Ar n
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\*[Le]\ 5, 1 \*[Le]
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.Ar m
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\*[Le]\ 12, where week 5 means
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.Dq the\ last Ar d No day\ in\ month Ar m
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which may occur in either the fourth or the fifth week).
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Week 1 is the first week in which the
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.Ar d Ns 'th
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day occurs.
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Day zero is Sunday.
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.El
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The
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.Cm time
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has the same format as
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.Cm offset
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except that no leading sign
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.Dq -
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or
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.Dq +
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is allowed.
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The default, if
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.Cm time
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is not given, is
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.Cm 02:00:00 .
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.El
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If no
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.Cm rule
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is present in
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.Ev TZ ,
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the rules specified by the
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.Xr tzfile 5
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format file
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.Pa posixrules
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in
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.Pa /usr/share/zoneinfo
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are used, with the standard and summer time offsets from UTC replaced
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by those specified by the
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.Cm offset
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values in
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.Ev TZ .
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.Pp
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For compatibility with System V Release 3.1, a semicolon (;) may be
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used to separate the
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.Cm rule
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from the rest of the specification.
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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
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format file and cannot be interpreted as a direct specification, UTC
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is used.
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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 information directory
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.It Pa /usr/share/zoneinfo/posixrules
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used with POSIX-style TZ's
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.It Pa /usr/share/zoneinfo/GMT
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for UTC leap seconds
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.El
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.Pp
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If
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.Pa /usr/share/zoneinfo/GMT
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is absent, UTC 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 ctime 3 ,
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.Xr getenv 3 ,
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.Xr strftime 3 ,
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.Xr time 3 ,
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.Xr tzfile 5
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.Sh STANDARDS
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The
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.Fn tzset
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function conforms to
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.St -p1003.1-88 .
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.\" @(#)newtzset.3 8.2
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.\" This file is in the public domain, so clarified as of
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.\" 2009-05-17 by Arthur David Olson.
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