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ZDUMP(8) NetBSD System Manager's Manual ZDUMP(8)
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zdump -- timezone dumper
zdump [--version] [-v] [-V] [-c [loyear,]highyear] [timezone ...]
zdump -t [lotime,]hightime [zonename ...]
The zdump program prints the current time in each timezone named on the
--version Output version information and exit.
--help Output short usage message and exit.
-i Output a description of time intervals. For each timezone on
the command line, output an interval-format description of the
timezone. See INTERVAL FORMAT below.
-v Output a verbose description of time intervals. For each
timezon on the command line, print the times at the two
extreme time values, the times (if present) at and just beyond
the boundaries of years that localtime(3) and gmtime(3) can
represent, and the times both one second before and exactly at
each detected time discontinuity. Each line is followed by
isdst=D where 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 fol-
lowed by gmtoff=N if the given local time is known to be N
seconds east of Greenwich.
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. Cutoffs
are at the start of each year, where the lower-bound timestamp
is inclusive and the upper is exclusive; for example, -c
1970,2070 selects transitions on or after 1970-01-01 00:00:00
UTC and before 2070-01-01 00:00:00 UTC. The default cutoff is
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 timezone determines whether the count includes
leap seconds. As with -c, the cutoff's lower bound is inclu-
sive and its upper bound is exclusive.
-V Like -v, except omit output concerning extreme time and year
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 ``TZ=string'' where string is a double-quoted string giving the
timezone, a second line ``- - interval'' describing the time interval
before the first transition if any, and zero or more following lines
``date time interval'' one line for each transition time and following
interval. Fields are separated by single tabs.
Dates are in yyyy-mm-dd format and times are in 24-hour hhmmss format
where hh < 24. Times are in local time immediately after the transition.
A time interval description consists of a UT offset in signed +- 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.
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 ``-'' or is ``zzz''.
In double-quoted strings, escape sequences represent unusual characters.
The escape sequences are \s for space, and \", \\, \f, \n, \r, \t, and \v
with their usual meaning in the C programming language. E.g., the dou-
ble-quoted string `CET\s\ \\"' represents the character sequence `CET'
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.)
- - -103126 LMT
1896-01-13 12:01:26 -1030 HST
1933-04-30 03 -0930 HDT 1
1933-05-21 11 -1030 HST
1942-02-09 03 -0930 HDT 1
1945-08-14 13:30 -0930 HPT 1
1945-09-30 01 -1030 HST
1947-06-08 02:30 -10 HST
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 fol-
lowing time interval is 10.5 hours west of UT, a standard time abbrevi-
ated 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:
- - +031212 LMT
1924-04-30 23:47:48 +03
1930-06-21 01 +04
1981-04-01 01 +05 1
1981-09-30 23 +04
2014-10-26 01 +03
2016-03-27 03 +04
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(3) at twelve-hour intervals. This works in all real-world
cases; one can construct artificial time zones for which this fails.
In the -v and -V output, ``UT'' denotes the value returned by gmtime(3),
which uses UTC for modern timestamps and some other UT flavor for time-
stamps that predate the introduction of UTC. No attempt is currently
made to have the output use ``UTC'' for newer and ``UT'' for older time-
stamps, partly because the exact date of the introduction of UTC is prob-
localtime(3), tzfile(5), zic(8)
NetBSD 10.99 October 22, 2021 NetBSD 10.99