ZDUMP(8) System Manager's Manual ZDUMP(8)
NAME
zdump – timezone dumper
SYNOPSIS
zdump [--help] [--version] [-ivV] [-c [loyear,]hiyear] [-t
[lotime,]hitime] [timezone ...]
DESCRIPTION
The zdump program prints the current time in each timezone named on the
command line.
The following options are available:
--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
timezone 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 followed
by gmtoff=N if the given local time is known to be N seconds east
of Greenwich.
-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.
-c [loyear,]hiyear
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
‘-500,2500’.
-t [lotime,]hitime
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 inclusive and
its upper bound is exclusive.
INTERVAL FORMAT
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 ‘hh : mm :
ss’ format where ‘hh <24’. Times are in local time immediately after the
transition. A time interval description consists of a UT offset in
signed ‘± hhmmss’ 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
double-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.)
TZ="Pacific/Honolulu"
- - -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 HWT 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
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:
TZ="Europe/Astrakhan"
- - +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.
LIMITATIONS
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
timestamps that predate the introduction of UTC. No attempt is currently
made to have the output use “UTC” for newer and “UT” for older
timestamps, partly because the exact date of the introduction of UTC is
problematic.
SEE ALSO
tzfile(5), zic(8)
macOS 15.2 December 15, 2022 macOS 15.2