man8/zdump.8

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   5 .TH zdump 8 2020-04-27 "" "Linux System Administration"
   6 .SH NAME
   7 zdump \- timezone dumper
   8 .SH SYNOPSIS
   9 .B zdump
  10 [
  11 .I option
  12 \&... ] [
  13 .I timezone
  14 \&... ]
  15 .SH DESCRIPTION
  16 .ie '\(lq'' .ds lq \&"\"
  17 .el .ds lq \(lq\"
  18 .ie '\(rq'' .ds rq \&"\"
  19 .el .ds rq \(rq\"
  20 .de q
  21 \\$3\*(lq\\$1\*(rq\\$2
  22 ..
  23 .ie \n(.g .ds - \f(CW-\fP
  24 .el ds - \-
  25 The
  26 .B zdump
  27 program prints the current time in each
  28 .I timezone
  29 named on the command line.
  30 .SH OPTIONS
  31 .TP
  32 .B \*-\*-version
  33 Output version information and exit.
  34 .TP
  35 .B \*-\*-help
  36 Output short usage message and exit.
  37 .TP
  38 .B \*-i
  39 Output a description of time intervals.  For each
  40 .I timezone
  41 on the command line, output an interval-format description of the
  42 timezone.  See
  43 .q "INTERVAL FORMAT"
  44 below.
  45 .TP
  46 .B \*-v
  47 Output a verbose description of time intervals.
  48 For each
  49 .I timezone
  50 on the command line,
  51 print the time at the lowest possible time value,
  52 the time one day after the lowest possible time value,
  53 the times both one second before and exactly at
  54 each detected time discontinuity,
  55 the time at one day less than the highest possible time value,
  56 and the time at the highest possible time value.
  57 Each line is followed by
  58 .BI isdst= D
  59 where
  60 .I D
  61 is positive, zero, or negative depending on whether
  62 the given time is daylight saving time, standard time,
  63 or an unknown time type, respectively.
  64 Each line is also followed by
  65 .BI gmtoff= N
  66 if the given local time is known to be
  67 .I N
  68 seconds east of Greenwich.
  69 .TP
  70 .B \*-V
  71 Like
  72 .BR \*-v ,
  73 except omit the times relative to the extreme time values.
  74 This generates output that is easier to compare to that of
  75 implementations with different time representations.
  76 .TP
  77 .BI "\*-c " \fR[\fIloyear , \fR]\fIhiyear
  78 Cut off interval output at the given year(s).
  79 Cutoff times are computed using the proleptic Gregorian calendar with year 0
  80 and with Universal Time (UT) ignoring leap seconds.
  81 Cutoffs are at the start of each year, where the lower-bound
  82 timestamp is exclusive and the upper is inclusive; for example,
  83 .B "\*-c 1970,2070"
  84 selects transitions after 1970-01-01 00:00:00 UTC
  85 and on or before 2070-01-01 00:00:00 UTC.
  86 The default cutoff is
  87 .BR \*-500,2500 .
  88 .TP
  89 .BI "\*-t " \fR[\fIlotime , \fR]\fIhitime
  90 Cut off interval output at the given time(s),
  91 given in decimal seconds since 1970-01-01 00:00:00
  92 Coordinated Universal Time (UTC).
  93 The
  94 .I timezone
  95 determines whether the count includes leap seconds.
  96 As with
  97 .BR \*-c ,
  98 the cutoff's lower bound is exclusive and its upper bound is inclusive.
  99 .SH "INTERVAL FORMAT"
 100 The interval format is a compact text representation that is intended
 101 to be both human- and machine-readable.  It consists of an empty line,
 102 then a line
 103 .q "TZ=\fIstring\fP"
 104 where
 105 .I string
 106 is a double-quoted string giving the timezone, a second line
 107 .q "\*- \*- \fIinterval\fP"
 108 describing the time interval before the first transition if any, and
 109 zero or more following lines
 110 .q "\fIdate time interval\fP",
 111 one line for each transition time and following interval.  Fields are
 112 separated by single tabs.
 113 .PP
 114 Dates are in
 115 .IR yyyy - mm - dd
 116 format and times are in 24-hour
 117 .IR hh : mm : ss
 118 format where
 119 .IR hh <24.
 120 Times are in local time immediately after the transition.  A
 121 time interval description consists of a UT offset in signed
 122 .RI \(+- hhmmss
 123 format, a time zone abbreviation, and an isdst flag.  An abbreviation
 124 that equals the UT offset is omitted; other abbreviations are
 125 double-quoted strings unless they consist of one or more alphabetic
 126 characters.  An isdst flag is omitted for standard time, and otherwise
 127 is a decimal integer that is unsigned and positive (typically 1) for
 128 daylight saving time and negative for unknown.
 129 .PP
 130 In times and in UT offsets with absolute value less than 100 hours,
 131 the seconds are omitted if they are zero, and
 132 the minutes are also omitted if they are also zero.  Positive UT
 133 offsets are east of Greenwich.  The UT offset \*-00 denotes a UT
 134 placeholder in areas where the actual offset is unspecified; by
 135 convention, this occurs when the UT offset is zero and the time zone
 136 abbreviation begins with
 137 .q "\*-"
 138 or is
 139 .q "zzz".
 140 .PP
 141 In double-quoted strings, escape sequences represent unusual
 142 characters.  The escape sequences are \es for space, and \e", \e\e,
 143 \ef, \en, \er, \et, and \ev with their usual meaning in the C
 144 programming language.  E.g., the double-quoted string
 145 \*(lq"CET\es\e"\e\e"\*(rq represents the character sequence \*(lqCET
 146 "\e\*(rq.\""
 147 .PP
 148 .ne 9
 149 Here is an example of the output, with the leading empty line omitted.
 150 (This example is shown with tab stops set far enough apart so that the
 151 tabbed columns line up.)
 152 .nf
 153 .sp
 154 .if \n(.g .ft CW
 155 .if t .in +.5i
 156 .if n .in +2
 157 .nr w \w'1896-01-13  'u+\n(.i
 158 .ta \w'1896-01-13  'u +\w'12:01:26  'u +\w'-103126  'u +\w'HWT  'u
 159 TZ="Pacific/Honolulu"
 160 -       -       -103126 LMT
 161 1896-01-13      12:01:26        -1030   HST
 162 1933-04-30      03      -0930   HDT     1
 163 1933-05-21      11      -1030   HST
 164 1942-02-09      03      -0930   HWT     1
 165 1945-08-14      13:30   -0930   HPT     1
 166 1945-09-30      01      -1030   HST
 167 1947-06-08      02:30   -10     HST
 168 .in
 169 .if \n(.g .ft
 170 .sp
 171 .fi
 172 Here, local time begins 10 hours, 31 minutes and 26 seconds west of
 173 UT, and is a standard time abbreviated LMT.  Immediately after the
 174 first transition, the date is 1896-01-13 and the time is 12:01:26, and
 175 the following time interval is 10.5 hours west of UT, a standard time
 176 abbreviated HST.  Immediately after the second transition, the date is
 177 1933-04-30 and the time is 03:00:00 and the following time interval is
 178 9.5 hours west of UT, is abbreviated HDT, and is daylight saving time.
 179 Immediately after the last transition the date is 1947-06-08 and the
 180 time is 02:30:00, and the following time interval is 10 hours west of
 181 UT, a standard time abbreviated HST.
 182 .PP
 183 .ne 10
 184 Here are excerpts from another example:
 185 .nf
 186 .sp
 187 .if \n(.g .ft CW
 188 .if t .in +.5i
 189 .if n .in +2
 190 TZ="Europe/Astrakhan"
 191 -       -       +031212 LMT
 192 1924-04-30      23:47:48        +03
 193 1930-06-21      01      +04
 194 1981-04-01      01      +05             1
 195 1981-09-30      23      +04
 196 \&...
 197 2014-10-26      01      +03
 198 2016-03-27      03      +04
 199 .in
 200 .if \n(.g .ft
 201 .sp
 202 .fi
 203 This time zone is east of UT, so its UT offsets are positive.  Also,
 204 many of its time zone abbreviations are omitted since they duplicate
 205 the text of the UT offset.
 206 .SH LIMITATIONS
 207 Time discontinuities are found by sampling the results returned by localtime
 208 at twelve-hour intervals.
 209 This works in all real-world cases;
 210 one can construct artificial time zones for which this fails.
 211 .PP
 212 In the
 213 .B \*-v
 214 and
 215 .B \*-V
 216 output,
 217 .q "UT"
 218 denotes the value returned by
 219 .BR gmtime (3),
 220 which uses UTC for modern timestamps and some other UT flavor for
 221 timestamps that predate the introduction of UTC.
 222 No attempt is currently made to have the output use
 223 .q "UTC"
 224 for newer and
 225 .q "UT"
 226 for older timestamps, partly because the exact date of the
 227 introduction of UTC is problematic.
 228 .SH SEE ALSO
 229 .BR tzfile (5),
 230 .BR zic (8)
 231 .\" This file is in the public domain, so clarified as of
 232 .\" 2009-05-17 by Arthur David Olson.