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75411d1572
MFC after: 3 weeks Sponsored by: Klara, Inc. Reviewed by: philip Differential Revision: https://reviews.freebsd.org/D39712
229 lines
6.4 KiB
Groff
229 lines
6.4 KiB
Groff
.\" 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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.Dd December 15, 2022
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.Dt ZDUMP 8
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.Os
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.Sh NAME
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.Nm zdump
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.Nd timezone dumper
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.Sh SYNOPSIS
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.Nm
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.Op Fl -help
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.Op Fl -version
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.Op Fl ivV
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.Oo
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.Fl c
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.Op Ar loyear , Ns
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.Ar hiyear
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.Oc
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.Oo
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.Fl t
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.Op Ar lotime , Ns
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.Ar hitime
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.Oc
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.Op Ar timezone ...
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.Sh DESCRIPTION
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The
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.Nm
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program prints the current time in each
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.Ar timezone
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named on the command line.
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.Pp
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The following options are available:
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.Bl -tag -width indent
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.It Fl -version
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Output version information and exit.
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.It Fl -help
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Output short usage message and exit.
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.It Fl i
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Output a description of time intervals.
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For each
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.Ar timezone
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on the command line, output an interval-format description of the
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timezone.
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See
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.Sx "INTERVAL FORMAT"
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below.
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.It Fl v
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Output a verbose description of time intervals.
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For each
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.Ar timezone
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on the command line,
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print the times at the two extreme time values,
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the times (if present) at and just beyond the boundaries of years that
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.Xr localtime 3
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and
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.Xr gmtime 3
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can represent, and
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the times both one second before and exactly at
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each detected time discontinuity.
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Each line is followed by
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.Cm isdst= Ns Ar D
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where
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.Ar D
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is positive, zero, or negative depending on whether
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the given time is daylight saving time, standard time,
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or an unknown time type, respectively.
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Each line is also followed by
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.Cm gmtoff= Ns Ar N
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if the given local time is known to be
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.Ar N
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seconds east of Greenwich.
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.It Fl V
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Like
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.Fl v ,
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except omit output concerning extreme time and year values.
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This generates output that is easier to compare to that of
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implementations with different time representations.
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.It Fl c Oo Ar loyear , Oc Ns Ar hiyear
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Cut off interval output at the given year(s).
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Cutoff times are computed using the proleptic Gregorian calendar with year 0
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and with Universal Time (UT) ignoring leap seconds.
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Cutoffs are at the start of each year, where the lower-bound
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timestamp is inclusive and the upper is exclusive; for example,
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.Ql "-c 1970,2070"
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selects transitions on or after 1970-01-01 00:00:00 UTC
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and before 2070-01-01 00:00:00 UTC.
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The default cutoff is
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.Ql -500,2500 .
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.It Fl t Oo Ar lotime , Oc Ns Ar hitime
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Cut off interval output at the given time(s),
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given in decimal seconds since 1970-01-01 00:00:00
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Coordinated Universal Time (UTC).
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The
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.Ar timezone
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determines whether the count includes leap seconds.
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As with
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.Fl c ,
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the cutoff's lower bound is inclusive and its upper bound is exclusive.
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.El
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.Sh "INTERVAL FORMAT"
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The interval format is a compact text representation that is intended
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to be both human- and machine-readable.
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It consists of an empty line,
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then a line
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.Dq "TZ=\fIstring\fP"
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where
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.Ar string
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is a double-quoted string giving the timezone, a second line
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.Dq "\*- \*- \fIinterval\fP"
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describing the time interval before the first transition if any, and
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zero or more following lines
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.Dq "\fIdate time interval\fP",
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one line for each transition time and following interval.
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Fields are
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separated by single tabs.
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.Pp
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Dates are in
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.Ql "yyyy - mm - dd"
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format and times are in 24-hour
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.Ql "hh : mm : ss"
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format where
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.Ql "hh <24" .
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Times are in local time immediately after the transition.
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A
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time interval description consists of a UT offset in signed
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.Ql "\(+- hhmmss"
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format, a time zone abbreviation, and an isdst flag.
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An abbreviation
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that equals the UT offset is omitted; other abbreviations are
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double-quoted strings unless they consist of one or more alphabetic
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characters.
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An isdst flag is omitted for standard time, and otherwise
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is a decimal integer that is unsigned and positive (typically 1) for
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daylight saving time and negative for unknown.
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.Pp
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In times and in UT offsets with absolute value less than 100 hours,
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the seconds are omitted if they are zero, and
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the minutes are also omitted if they are also zero.
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Positive UT
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offsets are east of Greenwich.
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The UT offset \*-00 denotes a UT
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placeholder in areas where the actual offset is unspecified; by
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convention, this occurs when the UT offset is zero and the time zone
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abbreviation begins with
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.Dq "-"
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or is
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.Dq "zzz".
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.Pp
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In double-quoted strings, escape sequences represent unusual
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characters.
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The escape sequences are \es for space, and \e", \e\e,
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\ef, \en, \er, \et, and \ev with their usual meaning in the C
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programming language.
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E.g., the double-quoted string
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\*(lq"CET\es\e"\e\e"\*(rq represents the character sequence \*(lqCET
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"\e\*(rq.\""
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.Pp
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Here is an example of the output, with the leading empty line omitted.
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(This example is shown with tab stops set far enough apart so that the
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tabbed columns line up.)
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.Bd -literal -offset indent
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TZ="Pacific/Honolulu"
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- - -103126 LMT
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1896-01-13 12:01:26 -1030 HST
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1933-04-30 03 -0930 HDT 1
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1933-05-21 11 -1030 HST
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1942-02-09 03 -0930 HWT 1
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1945-08-14 13:30 -0930 HPT 1
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1945-09-30 01 -1030 HST
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1947-06-08 02:30 -10 HST
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.Ed
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.Pp
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Here, local time begins 10 hours, 31 minutes and 26 seconds west of
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UT, and is a standard time abbreviated LMT.
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Immediately after the
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first transition, the date is 1896-01-13 and the time is 12:01:26, and
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the following time interval is 10.5 hours west of UT, a standard time
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abbreviated HST.
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Immediately after the second transition, the date is
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1933-04-30 and the time is 03:00:00 and the following time interval is
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9.5 hours west of UT, is abbreviated HDT, and is daylight saving time.
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Immediately after the last transition the date is 1947-06-08 and the
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time is 02:30:00, and the following time interval is 10 hours west of
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UT, a standard time abbreviated HST.
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.Pp
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Here are excerpts from another example:
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.Bd -literal -offset indent
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TZ="Europe/Astrakhan"
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- - +031212 LMT
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1924-04-30 23:47:48 +03
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1930-06-21 01 +04
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1981-04-01 01 +05 1
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1981-09-30 23 +04
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\&...
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2014-10-26 01 +03
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2016-03-27 03 +04
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.Ed
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.Pp
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This time zone is east of UT, so its UT offsets are positive.
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Also,
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many of its time zone abbreviations are omitted since they duplicate
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the text of the UT offset.
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.Sh LIMITATIONS
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Time discontinuities are found by sampling the results returned by
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.Xr localtime 3
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at twelve-hour intervals.
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This works in all real-world cases;
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one can construct artificial time zones for which this fails.
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.Pp
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In the
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.Fl v
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and
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.Fl V
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output,
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.Dq "UT"
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denotes the value returned by
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.Xr gmtime 3 ,
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which uses UTC for modern timestamps and some other UT flavor for
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timestamps that predate the introduction of UTC.
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No attempt is currently made to have the output use
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.Dq "UTC"
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for newer and
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.Dq "UT"
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for older timestamps, partly because the exact date of the
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introduction of UTC is problematic.
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.Sh SEE ALSO
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.Xr tzfile 5 ,
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.Xr zic 8
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