xref: /third_party/tzdata/zdump.8.txt

zdump(8)                    System Manager's Manual                   zdump(8)

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 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)

Time Zone Database                                                    zdump(8)