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https://frontier.innolan.net/rainlance/amiga-tz.git
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8f58b53628
(Thanks to Ken Rylander for the heads-up.) * australasia (Fiji): Assume Nov Sun>=1 2:00 to Jan Sun>=18 3:00 from here on out. * newtzset.3: Adjust Fiji example to match current assumptions. * NEWS: Document this.
327 lines
8.0 KiB
Groff
327 lines
8.0 KiB
Groff
.TH NEWTZSET 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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.ie \n(.g .ds - \f(CW-\fP
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.el ds - \-
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.B #include <time.h>
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.PP
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.B timezone_t tzalloc(char const *TZ);
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.PP
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.B void tzfree(timezone_t tz);
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.PP
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.B void tzset(void);
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.PP
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.B cc ... \*-ltz
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.fi
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.SH DESCRIPTION
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.ie '\(en'' .ds en \-
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.el .ds en \(en
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.ie '\(lq'' .ds lq \&"\"
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.el .ds lq \(lq\"
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.ie '\(rq'' .ds rq \&"\"
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.el .ds rq \(rq\"
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.de q
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\\$3\*(lq\\$1\*(rq\\$2
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..
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.I Tzalloc
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allocates and returns a time zone object described by
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.BR TZ .
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If
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.B TZ
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is not a valid time zone description, or if the object cannot be allocated,
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.I tzalloc
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returns a null pointer and sets
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.BR errno .
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.PP
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.I Tzfree
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frees a time zone object
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.BR tz ,
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which should have been successfully allocated by
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.IR tzalloc .
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This invalidates any
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.B tm_zone
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pointers that
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.B tz
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was used to set.
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.PP
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.I Tzset
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acts like
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.BR tzalloc(getenv("TZ")) ,
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except it saves any resulting time zone object into internal
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storage that is accessed by
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.IR localtime ,
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.IR localtime_r ,
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and
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.IR mktime .
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The anonymous shared time zone object is freed by the next call to
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.IR tzset .
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If the implied call to
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.B tzalloc
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fails,
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.I tzset
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falls back on UTC.
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.PP
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If
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.B TZ
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is null, the best available approximation to local wall
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clock time, as specified 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.
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If
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.B TZ
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is the empty string,
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Universal Time (UT) is used, with the abbreviation "UTC"
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and without leap second correction; please see
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.IR newctime (3)
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for more about UT, UTC, and leap seconds. If
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.B TZ
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is nonnull and nonempty:
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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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ASCII minus
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.RB ( \*- ),
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ASCII plus
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.RB ( + ),
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and NUL bytes 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) \*(en if present \*(en between zero and 59. If preceded by a
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.q "\*-" ,
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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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.q "+" .
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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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As an extension to POSIX, daylight saving is assumed to be in effect
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all year if it begins January 1 at 00:00 and ends December 31 at
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24:00 plus the difference between daylight saving and standard time,
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leaving no room for standard time in the calendar.
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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 \*(en including leap
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years \*(en 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
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.q "the last \fId\fP day in month \fIm\fP"
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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 POSIX does not allow a leading sign (\c
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.q "\*-"
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or
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.q "+" ).
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As an extension to POSIX, the hours part of
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.I time
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can range from \-167 through 167; this allows for unusual rules such
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as
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.q "the Saturday before the first Sunday of March" .
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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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Here are some examples of
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.B TZ
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values that directly specify the time zone rules; they use some of the
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extensions to POSIX.
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.TP
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.B EST5
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stands for US Eastern Standard
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Time (EST), 5 hours behind UTC, without daylight saving.
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.TP
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.B FJT\*-12FJST,M11.1.0,M1.3.4/75
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stands for Fiji Time (FJT) and Fiji Summer Time (FJST), 12 hours ahead
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of UTC, springing forward on November's first Sunday at 02:00, and
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falling back on January's third Thursday at 75:00 (i.e., 03:00 on the
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first Sunday on or after January 18).
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.TP
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.B IST\*-2IDT,M3.4.4/26,M10.5.0
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stands for Israel Standard Time (IST) and Israel Daylight Time (IDT),
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2 hours ahead of UTC, springing forward on March's fourth
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Thursday at 26:00 (i.e., 02:00 on the first Friday on or after March
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23), and falling back on October's last Sunday at 02:00.
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.TP
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.B WART4WARST,J1/0,J365/25
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stands for Western Argentina Summer Time (WARST), 3 hours behind UTC.
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There is a dummy fall-back transition on December 31 at 25:00 daylight
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saving time (i.e., 24:00 standard time, equivalent to January 1 at
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00:00 standard time), and a simultaneous spring-forward transition on
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January 1 at 00:00 standard time, so daylight saving time is in effect
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all year and the initial
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.B WART
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is a placeholder.
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.TP
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.B WGT3WGST,M3.5.0/\*-2,M10.5.0/\*-1
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stands for Western Greenland Time (WGT) and Western Greenland Summer
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Time (WGST), 3 hours behind UTC, where clocks follow the EU rules of
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springing forward on March's last Sunday at 01:00 UTC (\-02:00 local
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time) and falling back on October's last Sunday at 01:00 UTC
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(\-01:00 local time).
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.PP
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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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.SH FILES
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.ta \w'/usr/local/etc/zoneinfo/posixrules\0\0'u
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/usr/local/etc/zoneinfo time zone information directory
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.br
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/usr/local/etc/zoneinfo/localtime local time zone file
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.br
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/usr/local/etc/zoneinfo/posixrules used with POSIX-style TZ's
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.br
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/usr/local/etc/zoneinfo/GMT for UTC leap seconds
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.sp
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If
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.B /usr/local/etc/zoneinfo/GMT
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is absent,
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UTC leap seconds are loaded from
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.BR /usr/local/etc/zoneinfo/posixrules .
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.SH SEE ALSO
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getenv(3),
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newctime(3),
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newstrftime(3),
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time(2),
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tzfile(5)
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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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