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NAME
zdump - timezone dumper
SYNOPSIS
zdump [ option ... ] [ timezone ... ]
DESCRIPTION
The zdump program prints the current time in each timezone named on the command line.
OPTIONS
--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 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 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 the times relative to the extreme time 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
exclusive and the upper is inclusive; for example, -c 1970,2070 selects transitions
after 1970-01-01 00:00:00 UTC and on or 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
exclusive and its upper bound is inclusive.
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 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)
2020-04-27 zdump(8)