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Update to 2018f:

  Changes to code

    zic now always generates TZif files where time type 0 is used for
    timestamps before the first transition.  This simplifies the
    reading of TZif files and should not affect behavior of existing
    TZif readers because the same set of time types is used; only
    their internal indexes may have changed.  This affects only the
    legacy zones EST5EDT, CST6CDT, MST7MDT, PST8PDT, CET, MET, and
    EET, which previously used nonzero types for these timestamps.

    Because of the type 0 change, zic no longer outputs a dummy
    transition at time -2**59 (before the Big Bang), as clients should
    no longer need this to handle historical timestamps correctly.
    This reverts a change introduced in 2013d and shrinks most TZif
    files by a few bytes.

    zic now supports negative time-of-day in Rule and Leap lines, e.g.,
    "Rule X min max - Apr lastSun -6:00 1:00 -" means the transition
    occurs at 18:00 on the Saturday before the last Sunday in April.
    This behavior was documented in 2018a but the code did not
    entirely match the documentation.

    localtime.c no longer requires at least one time type in TZif
    files that lack transitions or have a POSIX-style TZ string.  This
    future-proofs the code against possible future extensions to the
    format that would allow TZif files with POSIX-style TZ strings and
    without transitions or time types.

    A read-access subscript error in localtime.c has been fixed.
    It could occur only in TZif files with timecnt == 0, something that
    does not happen in practice now but could happen in future versions.

    localtime.c no longer ignores TZif POSIX-style TZ strings that
    specify only standard time.  Instead, these TZ strings now
    override the default time type for timestamps after the last
    transition (or for all time stamps if there are no transitions),
    just as DST strings specifying DST have always done.

    leapseconds.awk now outputs "#updated" and "#expires" comments,
    and supports leap seconds at the ends of months other than June
    and December.  (Inspired by suggestions from Chris Woodbury.)

  Changes to documentation

    New restrictions: A Rule name must start with a character that
    is neither an ASCII digit nor "-" nor "+", and an unquoted name
    should not use characters in the set "!$%&'()*,/:;<=>?@[\]^`{|}~".
    The latter restriction makes room for future extensions (a
    possibility noted by Tom Lane).

    tzfile.5 now documents what time types apply before the first and
    after the last transition, if any.

    Documentation now uses the spelling "timezone" for a TZ setting
    that determines timestamp history, and "time zone" for a
    geographic region currently sharing the same standard time.

    The name "TZif" is now used for the tz binary data format.

    tz-link.htm now mentions the A0 TimeZone Migration utilities.
    (Thanks to Aldrin Martoq for the link.)

.\"	$NetBSD: zdump.8,v 1.18 2018/10/19 23:05:35 christos Exp $
.Dd October 19, 2018
.Dt ZDUMP 8
.Os
.Sh NAME
.Nm zdump
.Nd timezone dumper
.Sh SYNOPSIS
.Nm zdump
.Op Fl \-version
.Op Fl v
.Op Fl V
.Op Fl c Ar [loyear,]highyear
.Op Ar timezone ...
.Nm zdump
.Fl t
.Ar [lotime,]hightime
.Op Ar zonename ...
.Sh DESCRIPTION
The
.Nm
program prints the current time in each
.Ar timezone
named on the command line.
.SH OPTIONS
.Bl -tag -width XXXXXXXXX -compact
.It Fl \-version
Output version information and exit.
.It Fl \-help
Output short usage message and exit.
.It Fl i
Output a description of time intervals.
For each
.Ar timezone
on the command line, output an interval-format description of the
timezone.
See
.Sx "INTERVAL FORMAT"
below.
.It Fl v
Output a verbose description of time intervals.
For each
.Ar timezon
on the command line,
print the time at the lowest possible time value,
the time one day after the lowest possible time value,
the times both one second before and exactly at
each detected time discontinuity,
the time at one day less than the highest possible time value,
and the time at the highest possible time value.
Each line is followed by
.Em isdst=D
where
.Em D
is positive, zero, or negative depending on whether
the given time is daylight saving time, standard time,
or an unknown time type, respectively.
Each line is also followed by
.Em gmtoff=N
if the given local time is known to be
.Em N
seconds east of Greenwich.
.It Fl c Ar [loyear,]highyear
Cut off interval output at the given year(s).
Cutoff times are computed using the proleptic Gregorian calendar with year 0
and with Universal Time (UT) ignoring leap seconds.
The lower bound is exclusive and the upper is inclusive; for example, a
.Em loyear
of 1970 excludes a transition occurring at 1970-01-01 00:00:00 UTC but a
.Em hiyear
of 1970 includes the transition.
The default cutoff is
.Em \&-500,2500 .
.It Fl t Ar [lotime,]hightime
Cut off interval output at the given time(s),
given in decimal seconds since 1970-01-01 00:00:00
Coordinated Universal Time (UTC).
The
.Ar timezone
determines whether the count includes leap seconds.
As with
.Fl c ,
the cutoff's lower bound is exclusive and its upper bound is inclusive.
.It Fl V
Like
.Fl v ,
except omit the times relative to the extreme time values.
This generates output that is easier to compare to that of
implementations with different time representations.
.El
.Sh "INTERVAL FORMAT"
.Pp
The interval format is a compact text representation that is intended
to be both human- and machine-readable.
It consists of an empty line, then a line
.Dq TZ=string
where
.Dv string
is a double-quoted string giving the timezone, a second line
.Dq \&- \&- interval
describing the time interval before the first transition if any, and
zero or more following lines
.Dq date time interval
one line for each transition time and following interval.
Fields are separated by single tabs.
.Pp
Dates are in
.Dv yyyy-mm-dd
format and times are in 24-hour
.Dv hhmmss
format where
.Dv hh < 24 .
Times are in local time immediately after the transition.
A time interval description consists of a UT offset in signed
.Dv \&+- hh : mm : ss
format, a time zone abbreviation, and an isdst flag.
An abbreviation that equals the UT offset is omitted; other abbreviations are
double-quoted strings unless they consist of one or more alphabetic
characters.
An isdst flag is omitted for standard time, and otherwise
is a decimal integer that is unsigned and positive (typically 1) for
daylight saving time and negative for unknown.
.Pp
In times and in UT offsets with absolute value less than 100 hours,
the seconds are omitted if they are zero, and
the minutes are also omitted if they are also zero.
Positive UT offsets are east of Greenwich.  The UT offset \&-00 denotes a UT
placeholder in areas where the actual offset is unspecified; by
convention, this occurs when the UT offset is zero and the time zone
abbreviation begins with
.Dq \&-
or is
.Dq zzz .
.Pp
In double-quoted strings, escape sequences represent unusual
characters.  The escape sequences are \es for space, and \e", \e\e,
\ef, \en, \er, \et, and \ev with their usual meaning in the C
programming language.
E.g., the double-quoted string
.Sq "CET\es\e"\e\e"
represents the character sequence
.Sq CET
.Pp
Here is an example of the output, with the leading empty line omitted.
(This example is shown with tab stops set far enough apart so that the
tabbed columns line up.)
.Bd -literal
TZ="Pacific/Honolulu"
.Ed
.Bl -column "XXXX-XX-XX" "HH:MM:SS" "-HH:MM:SS" "TZT" "X" -compact
.It - Ta - Ta -10:31:26 Ta LMT Ta
.It 1896-01-13 Ta 12:01:26 Ta -10:30 Ta HST Ta
.It 1933-04-30 Ta 03 Ta -09:30 Ta HDT Ta 1
.It 1933-05-21 Ta 11 Ta -10:30 Ta HST Ta
.It 1942-02-09 Ta 03 Ta -09:30 Ta HDT Ta 1
.It 1945-09-30 Ta 01 Ta -10:30 Ta HST Ta
.It 1947-06-08 Ta 02:30 Ta -10 Ta HST Ta
.El
.Pp
Here, local time begins 10 hours, 31 minutes and 26 seconds west of
UT, and is a standard time abbreviated LMT.  Immediately after the
first transition, the date is 1896-01-13 and the time is 12:01:26, and
the following time interval is 10.5 hours west of UT, a standard time
abbreviated HST.
Immediately after the second transition, the date is
1933-04-30 and the time is 03:00:00 and the following time interval is
9.5 hours west of UT, is abbreviated HDT, and is daylight saving time.
Immediately after the last transition the date is 1947-06-08 and the
time is 02:30:00, and the following time interval is 10 hours west of
UT, a standard time abbreviated HST.
.Pp
Here are excerpts from another example:
.Bd -literal
TZ="Europe/Astrakhan"
.Ed
.Bl -column "XXXX-XX-XX" "HH:MM:SS" "-HH:MM:SS" "TZT" "X" -compact
.It - Ta - Ta +03:12:12 Ta LMT Ta
.It 1924-04-30 Ta 23:47:48 Ta +03 Ta Ta
.It 1930-06-21 Ta 01 Ta +04 Ta Ta
.It 1981-04-01 Ta 01 Ta +05 Ta Ta 1
.It 1981-09-30 Ta 23 Ta +04 Ta Ta
.It \&... Ta Ta Ta Ta
.It 2014-10-26 Ta 01 Ta +03 Ta Ta
.It 2016-03-27 Ta 03 Ta +04 Ta Ta
.El
.Pp
This time zone is east of UT, so its UT offsets are positive.  Also,
many of its time zone abbreviations are omitted since they duplicate
the text of the UT offset.
.Sh LIMITATIONS
Time discontinuities are found by sampling the results returned by localtime
at twelve-hour intervals.
This works in all real-world cases;
one can construct artificial time zones for which this fails.
.Pp
In the
.Fl v
and
.Fl V
output,
.Dq UT
denotes the value returned by
.Xr gmtime 3 ,
which uses UTC for modern timestamps and some other UT flavor for
timestamps that predate the introduction of UTC.
No attempt is currently made to have the output use
.Dq UTC
for newer and
.Dq UT
for older timestamps, partly because the exact date of the
introduction of UTC is problematic.
.Sh SEE ALSO
.Xr tzfile 5 ,
.Xr zic 8
.\" @(#)zdump.8	8.2
.\" This file is in the public domain, so clarified as of
.\" 2009-05-17 by Arthur David Olson.