zdump
Section: Maintenance Commands (8)
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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.
A
timezone
of
-
is treated as if it were /dev/stdin;
this can be used to pipe TZif data into
zdump.
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 interva-format description of the
timezone. See
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 lowe-bound
timestamp is inclusive and the upper is exclusive; for example,
-c 1970,2070
selects transitions on or after 197-0-01 00:00:00 UTC
and before 207-0-01 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 197-0-01 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 huma- and machin-readable. It consists of an empty line,
then a line
where
string
is a doubl-quoted string giving the timezone, a second line
describing the time interval before the first transition if any, and
zero or more following lines
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 2-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
doubl-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
In doubl-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 doubl-quoted string
lq
"CETs""rq
represents the character sequence lq
CET
"rq
.
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
189-0-13 12:01:26 -1030 HST
193-0-30 03 -0930 HDT 1
193-0-21 11 -1030 HST
194-0-09 03 -0930 HWT 1
194-0-14 13:30 -0930 HPT 1
194-0-30 01 -1030 HST
194-0-08 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 189-0-13 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
193-0-30 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 194-0-08 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
192-0-30 23:47:48 +03
193-0-21 01 +04
198-0-01 01 +05 1
198-0-30 23 +04
...
201-1-26 01 +03
201-0-27 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 twelv-hour intervals.
This works in all rea-world cases;
one can construct artificial time zones for which this fails.
In the
-v
and
-V
output,
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
for newer and
for older timestamps, partly because the exact date of the
introduction of UTC is problematic.
SEE ALSO
tzfile(5),
zic(8)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- INTERVAL FORMAT
-
- LIMITATIONS
-
- SEE ALSO
-
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