243 lines
5.3 KiB
Groff
243 lines
5.3 KiB
Groff
.\" $NetBSD: tzset.3,v 1.10 2000/06/05 11:56:13 kleink Exp $
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.TH TZSET 3
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.SH NAME
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tzset \- initialize time conversion information
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.SH SYNOPSIS
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.nf
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.B void tzset(void)
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.PP
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.fi
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.SH DESCRIPTION
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.I Tzset
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uses the value of the environment variable
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.B TZ
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to set time conversion information used by
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.IR localtime .
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If
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.B 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 specified
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by the
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.IR tzfile (5)-format
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file
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.B localtime
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in the system time conversion information directory, is used by
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.IR localtime .
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If
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.B 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). If
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.B TZ
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appears in the environment and its value is not a null string:
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.IP
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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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.IP
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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 of
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the time conversion information.
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.PP
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When
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.B TZ
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is used as a pathname, if it begins with a slash,
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it is used as an absolute pathname; otherwise,
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it is used as a pathname relative to a system time conversion information
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directory.
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The file must be in the format specified in
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.IR tzfile (5).
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.PP
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When
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.B 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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.IP
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\fIstd\|offset\fR[\fIdst\fR[\fIoffset\fR][\fB,\fIrule\fR]]
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.PP
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Where:
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.RS
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.TP 15
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.IR std " and " dst
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Three or more bytes that are the designation for the standard
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.RI ( std )
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or summer
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.RI ( dst )
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time zone. Only
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.I std
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is required; if
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.I 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. Any characters
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except a leading colon
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.RB ( : ),
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digits, comma
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.RB ( , ),
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minus
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.RB ( \(mi ),
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plus
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.RB ( \(pl ),
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and ASCII NUL are allowed.
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.TP
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.I 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. The
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.I offset
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has the form:
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.RS
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.IP
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\fIhh\fR[\fB:\fImm\fR[\fB:\fIss\fR]]
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.RE
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.IP
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The minutes
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.RI ( mm )
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and seconds
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.RI ( ss )
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are optional. The hour
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.RI ( hh )
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is required and may be a single digit. The
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.I offset
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following
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.I std
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is required. If no
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.I offset
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follows
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.IR dst ,
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summer time is assumed to be one hour ahead of standard time. One or
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more digits may be used; the value is always interpreted as a decimal
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number. 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. If preceded by a
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.RB `` \(mi '',
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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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.RB `` \(pl '').
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.TP
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.I rule
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Indicates when to change to and back from summer time. The
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.I rule
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has the form:
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.RS
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.IP
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\fIdate\fB/\fItime\fB,\fIdate\fB/\fItime\fR
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.RE
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.IP
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where the first
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.I 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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.I date
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describes when the change back happens. Each
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.I 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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.IP
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The format of
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.I date
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is one of the following:
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.RS
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.TP 10
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.BI J n
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The Julian day
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.I n
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.RI "(1\ \(<=" "\ n\ " "\(<=\ 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. It is
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impossible to explicitly refer to the occasional February 29.
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.TP
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.I n
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The zero-based Julian day
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.RI "(0\ \(<=" "\ n\ " "\(<=\ 365).
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Leap days are counted, and it is possible to refer to February 29.
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.TP
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.BI M m . n . d
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The
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.IR d' th
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day
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.RI "(0\ \(<=" "\ d\ " "\(<=\ 6)
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of week
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.I n
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of month
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.I m
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of the year
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.RI "(1\ \(<=" "\ n\ " "\(<=\ 5,
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.RI "1\ \(<=" "\ m\ " "\(<=\ 12,
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where week 5 means ``the last
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.I d
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day in month
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.IR m ''
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which may occur in either the fourth or the fifth week). Week 1 is the
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first week in which the
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.IR d' th
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day occurs. Day zero is Sunday.
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.RE
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.IP "" 15
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The
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.I time
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has the same format as
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.I offset
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except that no leading sign
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.RB (`` \(mi ''
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or
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.RB `` \(pl '')
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is allowed. The default, if
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.I time
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is not given, is
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.BR 02:00:00 .
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.RE
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.LP
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If no
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.I rule
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is present in
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.BR TZ ,
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the rules specified
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by the
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.IR tzfile (5)-format
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file
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.B 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 UTC replaced by those specified by
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the
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.I offset
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values in
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.BR TZ .
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.PP
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For compatibility with System V Release 3.1, a semicolon
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.RB ( ; )
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may be used to separate the
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.I 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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.B TZ
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environment variable does not specify a
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.IR tzfile (5)-format
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and cannot be interpreted as a direct specification,
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UTC is used.
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.SH FILES
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.ta \w'/usr/share/zoneinfo/posixrules\0\0'u
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/etc/localtime local time zone file
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.br
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/usr/share/zoneinfo time zone information directory
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.br
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/usr/share/zoneinfo/posixrules used with POSIX-style TZ's
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.br
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/usr/share/zoneinfo/GMT for UTC leap seconds
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.sp
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If
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.B /usr/share/zoneinfo/GMT
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is absent,
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UTC leap seconds are loaded from
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.BR /usr/share/zoneinfo/posixrules .
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.SH SEE ALSO
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getenv(3),
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ctime(3),
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strftime(3),
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time(3),
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tzfile(5)
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.SH STANDARDS
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The
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tzset()
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function conforms to
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IEEE Std1003.1-1988 (``POSIX'').
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.\" @(#)newtzset.3 7.5
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