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145 lines
7.2 KiB
Plaintext
145 lines
7.2 KiB
Plaintext
zdump(8) System Manager's Manual zdump(8)
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NAME
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zdump - timezone dumper
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SYNOPSIS
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zdump [ option ... ] [ timezone ... ]
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DESCRIPTION
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The zdump program prints the current time in each timezone named on the
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command line.
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OPTIONS
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--version
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Output version information and exit.
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--help Output short usage message and exit.
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-i Output a description of time intervals. For each timezone on
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the command line, output an interval-format description of the
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timezone. See "INTERVAL FORMAT" below.
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-v Output a verbose description of time intervals. For each
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timezone on the command line, print the times at the two extreme
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time values, the times (if present) at and just beyond the
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boundaries of years that localtime(3) and gmtime(3) can
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represent, and the times both one second before and exactly at
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each detected time discontinuity. Each line is followed by
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isdst=D where D is positive, zero, or negative depending on
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whether the given time is daylight saving time, standard time,
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or an unknown time type, respectively. Each line is also
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followed by gmtoff=N if the given local time is known to be N
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seconds east of Greenwich.
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-V Like -v, except omit output concerning extreme time and year
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values. This generates output that is easier to compare to that
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of implementations with different time representations.
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-c [loyear,]hiyear
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Cut off interval output at the given year(s). Cutoff times are
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computed using the proleptic Gregorian calendar with year 0 and
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with Universal Time (UT) ignoring leap seconds. Cutoffs are at
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the start of each year, where the lower-bound timestamp is
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inclusive and the upper is exclusive; for example, -c 1970,2070
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selects transitions on or after 1970-01-01 00:00:00 UTC and
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before 2070-01-01 00:00:00 UTC. The default cutoff is
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-500,2500.
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-t [lotime,]hitime
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Cut off interval output at the given time(s), given in decimal
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seconds since 1970-01-01 00:00:00 Coordinated Universal Time
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(UTC). The timezone determines whether the count includes leap
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seconds. As with -c, the cutoff's lower bound is inclusive and
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its upper bound is exclusive.
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INTERVAL FORMAT
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The interval format is a compact text representation that is intended
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to be both human- and machine-readable. It consists of an empty line,
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then a line "TZ=string" where string is a double-quoted string giving
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the timezone, a second line "- - interval" describing the time interval
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before the first transition if any, and zero or more following lines
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"date time interval", one line for each transition time and following
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interval. Fields are separated by single tabs.
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Dates are in yyyy-mm-dd format and times are in 24-hour hh:mm:ss format
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where hh<24. Times are in local time immediately after the transition.
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A time interval description consists of a UT offset in signed +-hhmmss
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format, a time zone abbreviation, and an isdst flag. An abbreviation
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that equals the UT offset is omitted; other abbreviations are double-
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quoted strings unless they consist of one or more alphabetic
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characters. An isdst flag is omitted for standard time, and otherwise
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is a decimal integer that is unsigned and positive (typically 1) for
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daylight saving time and negative for unknown.
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In times and in UT offsets with absolute value less than 100 hours, the
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seconds are omitted if they are zero, and the minutes are also omitted
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if they are also zero. Positive UT offsets are east of Greenwich. The
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UT offset -00 denotes a UT placeholder in areas where the actual offset
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is unspecified; by convention, this occurs when the UT offset is zero
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and the time zone abbreviation begins with "-" or is "zzz".
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In double-quoted strings, escape sequences represent unusual
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characters. The escape sequences are \s for space, and \", \\, \f, \n,
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\r, \t, and \v with their usual meaning in the C programming language.
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E.g., the double-quoted string ""CET\s\"\\"" represents the character
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sequence "CET "\".
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Here is an example of the output, with the leading empty line omitted.
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(This example is shown with tab stops set far enough apart so that the
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tabbed columns line up.)
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TZ="Pacific/Honolulu"
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- - -103126 LMT
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1896-01-13 12:01:26 -1030 HST
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1933-04-30 03 -0930 HDT 1
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1933-05-21 11 -1030 HST
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1942-02-09 03 -0930 HWT 1
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1945-08-14 13:30 -0930 HPT 1
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1945-09-30 01 -1030 HST
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1947-06-08 02:30 -10 HST
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Here, local time begins 10 hours, 31 minutes and 26 seconds west of UT,
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and is a standard time abbreviated LMT. Immediately after the first
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transition, the date is 1896-01-13 and the time is 12:01:26, and the
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following time interval is 10.5 hours west of UT, a standard time
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abbreviated HST. Immediately after the second transition, the date is
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1933-04-30 and the time is 03:00:00 and the following time interval is
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9.5 hours west of UT, is abbreviated HDT, and is daylight saving time.
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Immediately after the last transition the date is 1947-06-08 and the
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time is 02:30:00, and the following time interval is 10 hours west of
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UT, a standard time abbreviated HST.
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Here are excerpts from another example:
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TZ="Europe/Astrakhan"
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- - +031212 LMT
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1924-04-30 23:47:48 +03
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1930-06-21 01 +04
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1981-04-01 01 +05 1
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1981-09-30 23 +04
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...
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2014-10-26 01 +03
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2016-03-27 03 +04
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This time zone is east of UT, so its UT offsets are positive. Also,
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many of its time zone abbreviations are omitted since they duplicate
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the text of the UT offset.
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LIMITATIONS
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Time discontinuities are found by sampling the results returned by
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localtime(3) at twelve-hour intervals. This works in all real-world
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cases; one can construct artificial time zones for which this fails.
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In the -v and -V output, "UT" denotes the value returned by gmtime(3),
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which uses UTC for modern timestamps and some other UT flavor for
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timestamps that predate the introduction of UTC. No attempt is
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currently made to have the output use "UTC" for newer and "UT" for
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older timestamps, partly because the exact date of the introduction of
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UTC is problematic.
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SEE ALSO
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tzfile(5), zic(8)
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Time Zone Database zdump(8)
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