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File: [cvs.NetBSD.org] / src / lib / libc / time / zdump.8 (download)

Revision 1.19, Sat Oct 27 22:29:24 2018 UTC (23 months, 4 weeks ago) by christos
Branch: MAIN
CVS Tags: phil-wifi-20200421, phil-wifi-20200411, phil-wifi-20200406, phil-wifi-20191119, phil-wifi-20190609, pgoyette-compat-20190127, pgoyette-compat-20190118, pgoyette-compat-1226, pgoyette-compat-1126, netbsd-9-base, netbsd-9-1-RELEASE, netbsd-9-0-RELEASE, netbsd-9-0-RC2, netbsd-9-0-RC1, netbsd-9, is-mlppp-base, is-mlppp
Changes since 1.18: +11 -10 lines

Welcome tzcode-2018g

  Changes to code

    When generating TZif files with leap seconds, zic no longer uses a
    format that trips up older 32-bit clients, fixing a bug introduced
    in 2018f.  (Reported by Daniel Fischer.)  Also, the zic workaround
    for QTBUG-53071 now also works for TZif files with leap seconds.

    The translator to rearguard format now rewrites the line
    "Rule Japan 1948 1951 - Sep Sat>=8 25:00 0 S" to
    "Rule Japan 1948 1951 - Sep Sun>=9  1:00 0 S".
    This caters to zic before 2007 and to Oracle TZUpdater 2.2.0
    and earlier.  (Reported by Christos Zoulas.)

  Changes to documentation

    tzfile.5 has new sections on interoperability issues.

.\"	$NetBSD: zdump.8,v 1.19 2018/10/27 22:29:24 christos Exp $
.Dd October 27, 2018
.Nm zdump
.Nd timezone dumper
.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 ...
program prints the current time in each
.Ar timezone
named on the command line.
.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
.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
.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).
.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
.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.
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
.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.
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
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.
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 .
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
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
.Bl -column "XXXX-XX-XX" "HH:MM:SS" "-HHMMSS" "TZT" "X" -compact
.It - Ta - Ta -103126 Ta LMT Ta
.It 1896-01-13 Ta 12:01:26 Ta -1030 Ta HST Ta
.It 1933-04-30 Ta 03 Ta -0930 Ta HDT Ta 1
.It 1933-05-21 Ta 11 Ta -1030 Ta HST Ta
.It 1942-02-09 Ta 03 Ta -0930 Ta HDT Ta 1
.It 1945-08-14 Ta 13:30 Ta -0930 Ta HPT Ta 1
.It 1945-09-30 Ta 01 Ta -1030 Ta HST Ta
.It 1947-06-08 Ta 02:30 Ta -10 Ta HST Ta
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.
Here are excerpts from another example:
.Bd -literal
.Bl -column "XXXX-XX-XX" "HH:MM:SS" "-HH:MM:SS" "TZT" "X" -compact
.It - Ta - Ta +031212 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
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.
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.
In the
.Fl v
.Fl V
.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
for newer and
.Dq UT
for older timestamps, partly because the exact date of the
introduction of UTC is problematic.
.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.