Annotation of src/lib/libc/time/zdump.8, Revision 1.19
1.19 ! christos 1: .\" $NetBSD: zdump.8,v 1.18 2018/10/19 23:05:35 christos Exp $
! 2: .Dd October 27, 2018
1.6 joerg 3: .Dt ZDUMP 8
1.4 wiz 4: .Os
5: .Sh NAME
6: .Nm zdump
1.18 christos 7: .Nd timezone dumper
1.4 wiz 8: .Sh SYNOPSIS
9: .Nm zdump
1.5 kleink 10: .Op Fl \-version
1.4 wiz 11: .Op Fl v
1.10 christos 12: .Op Fl V
1.7 mlelstv 13: .Op Fl c Ar [loyear,]highyear
1.18 christos 14: .Op Ar timezone ...
1.10 christos 15: .Nm zdump
16: .Fl t
1.13 christos 17: .Ar [lotime,]hightime
1.10 christos 18: .Op Ar zonename ...
1.4 wiz 19: .Sh DESCRIPTION
1.18 christos 20: The
1.4 wiz 21: .Nm
1.18 christos 22: program prints the current time in each
23: .Ar timezone
1.1 jtc 24: named on the command line.
1.18 christos 25: .SH OPTIONS
1.5 kleink 26: .Bl -tag -width XXXXXXXXX -compact
27: .It Fl \-version
28: Output version information and exit.
1.18 christos 29: .It Fl \-help
30: Output short usage message and exit.
1.15 christos 31: .It Fl i
32: Output a description of time intervals.
33: For each
1.18 christos 34: .Ar timezone
1.15 christos 35: on the command line, output an interval-format description of the
1.18 christos 36: timezone.
1.15 christos 37: See
38: .Sx "INTERVAL FORMAT"
39: below.
1.4 wiz 40: .It Fl v
1.15 christos 41: Output a verbose description of time intervals.
1.1 jtc 42: For each
1.18 christos 43: .Ar timezon
1.1 jtc 44: on the command line,
1.3 jtc 45: print the time at the lowest possible time value,
1.1 jtc 46: the time one day after the lowest possible time value,
47: the times both one second before and exactly at
48: each detected time discontinuity,
49: the time at one day less than the highest possible time value,
1.13 christos 50: and the time at the highest possible time value.
51: Each line is followed by
1.15 christos 52: .Em isdst=D
1.13 christos 53: where
1.15 christos 54: .Em D
1.13 christos 55: is positive, zero, or negative depending on whether
56: the given time is daylight saving time, standard time,
57: or an unknown time type, respectively.
58: Each line is also followed by
1.15 christos 59: .Em gmtoff=N
1.13 christos 60: if the given local time is known to be
1.15 christos 61: .Em N
1.13 christos 62: seconds east of Greenwich.
1.7 mlelstv 63: .It Fl c Ar [loyear,]highyear
1.15 christos 64: Cut off interval output at the given year(s).
1.13 christos 65: Cutoff times are computed using the proleptic Gregorian calendar with year 0
66: and with Universal Time (UT) ignoring leap seconds.
67: The lower bound is exclusive and the upper is inclusive; for example, a
1.15 christos 68: .Em loyear
1.14 christos 69: of 1970 excludes a transition occurring at 1970-01-01 00:00:00 UTC but a
1.15 christos 70: .Em hiyear
1.13 christos 71: of 1970 includes the transition.
72: The default cutoff is
1.15 christos 73: .Em \&-500,2500 .
1.13 christos 74: .It Fl t Ar [lotime,]hightime
1.15 christos 75: Cut off interval output at the given time(s),
1.13 christos 76: given in decimal seconds since 1970-01-01 00:00:00
77: Coordinated Universal Time (UTC).
78: The
1.18 christos 79: .Ar timezone
1.13 christos 80: determines whether the count includes leap seconds.
81: As with
82: .Fl c ,
83: the cutoff's lower bound is exclusive and its upper bound is inclusive.
1.10 christos 84: .It Fl V
85: Like
86: .Fl v ,
87: except omit the times relative to the extreme time values.
88: This generates output that is easier to compare to that of
89: implementations with different time representations.
1.4 wiz 90: .El
1.15 christos 91: .Sh "INTERVAL FORMAT"
92: .Pp
93: The interval format is a compact text representation that is intended
94: to be both human- and machine-readable.
95: It consists of an empty line, then a line
96: .Dq TZ=string
97: where
98: .Dv string
1.18 christos 99: is a double-quoted string giving the timezone, a second line
1.15 christos 100: .Dq \&- \&- interval
101: describing the time interval before the first transition if any, and
102: zero or more following lines
103: .Dq date time interval
104: one line for each transition time and following interval.
105: Fields are separated by single tabs.
106: .Pp
107: Dates are in
108: .Dv yyyy-mm-dd
109: format and times are in 24-hour
1.16 christos 110: .Dv hhmmss
1.15 christos 111: format where
1.17 wiz 112: .Dv hh < 24 .
1.15 christos 113: Times are in local time immediately after the transition.
114: A time interval description consists of a UT offset in signed
115: .Dv \&+- hh : mm : ss
116: format, a time zone abbreviation, and an isdst flag.
117: An abbreviation that equals the UT offset is omitted; other abbreviations are
118: double-quoted strings unless they consist of one or more alphabetic
119: characters.
120: An isdst flag is omitted for standard time, and otherwise
121: is a decimal integer that is unsigned and positive (typically 1) for
122: daylight saving time and negative for unknown.
123: .Pp
1.16 christos 124: In times and in UT offsets with absolute value less than 100 hours,
125: the seconds are omitted if they are zero, and
1.15 christos 126: the minutes are also omitted if they are also zero.
127: Positive UT offsets are east of Greenwich. The UT offset \&-00 denotes a UT
128: placeholder in areas where the actual offset is unspecified; by
129: convention, this occurs when the UT offset is zero and the time zone
130: abbreviation begins with
131: .Dq \&-
132: or is
133: .Dq zzz .
134: .Pp
135: In double-quoted strings, escape sequences represent unusual
136: characters. The escape sequences are \es for space, and \e", \e\e,
137: \ef, \en, \er, \et, and \ev with their usual meaning in the C
138: programming language.
139: E.g., the double-quoted string
140: .Sq "CET\es\e"\e\e"
141: represents the character sequence
142: .Sq CET
143: .Pp
144: Here is an example of the output, with the leading empty line omitted.
145: (This example is shown with tab stops set far enough apart so that the
146: tabbed columns line up.)
147: .Bd -literal
148: TZ="Pacific/Honolulu"
149: .Ed
1.19 ! christos 150: .Bl -column "XXXX-XX-XX" "HH:MM:SS" "-HHMMSS" "TZT" "X" -compact
! 151: .It - Ta - Ta -103126 Ta LMT Ta
! 152: .It 1896-01-13 Ta 12:01:26 Ta -1030 Ta HST Ta
! 153: .It 1933-04-30 Ta 03 Ta -0930 Ta HDT Ta 1
! 154: .It 1933-05-21 Ta 11 Ta -1030 Ta HST Ta
! 155: .It 1942-02-09 Ta 03 Ta -0930 Ta HDT Ta 1
! 156: .It 1945-08-14 Ta 13:30 Ta -0930 Ta HPT Ta 1
! 157: .It 1945-09-30 Ta 01 Ta -1030 Ta HST Ta
1.15 christos 158: .It 1947-06-08 Ta 02:30 Ta -10 Ta HST Ta
159: .El
160: .Pp
161: Here, local time begins 10 hours, 31 minutes and 26 seconds west of
162: UT, and is a standard time abbreviated LMT. Immediately after the
163: first transition, the date is 1896-01-13 and the time is 12:01:26, and
164: the following time interval is 10.5 hours west of UT, a standard time
165: abbreviated HST.
166: Immediately after the second transition, the date is
167: 1933-04-30 and the time is 03:00:00 and the following time interval is
168: 9.5 hours west of UT, is abbreviated HDT, and is daylight saving time.
169: Immediately after the last transition the date is 1947-06-08 and the
170: time is 02:30:00, and the following time interval is 10 hours west of
171: UT, a standard time abbreviated HST.
172: .Pp
173: Here are excerpts from another example:
174: .Bd -literal
175: TZ="Europe/Astrakhan"
176: .Ed
177: .Bl -column "XXXX-XX-XX" "HH:MM:SS" "-HH:MM:SS" "TZT" "X" -compact
1.19 ! christos 178: .It - Ta - Ta +031212 Ta LMT Ta
1.15 christos 179: .It 1924-04-30 Ta 23:47:48 Ta +03 Ta Ta
180: .It 1930-06-21 Ta 01 Ta +04 Ta Ta
181: .It 1981-04-01 Ta 01 Ta +05 Ta Ta 1
182: .It 1981-09-30 Ta 23 Ta +04 Ta Ta
183: .It \&... Ta Ta Ta Ta
184: .It 2014-10-26 Ta 01 Ta +03 Ta Ta
185: .It 2016-03-27 Ta 03 Ta +04 Ta Ta
186: .El
187: .Pp
188: This time zone is east of UT, so its UT offsets are positive. Also,
189: many of its time zone abbreviations are omitted since they duplicate
190: the text of the UT offset.
1.8 joerg 191: .Sh LIMITATIONS
1.7 mlelstv 192: Time discontinuities are found by sampling the results returned by localtime
193: at twelve-hour intervals.
194: This works in all real-world cases;
195: one can construct artificial time zones for which this fails.
1.11 christos 196: .Pp
1.15 christos 197: In the
198: .Fl v
199: and
200: .Fl V
201: output,
1.11 christos 202: .Dq UT
203: denotes the value returned by
204: .Xr gmtime 3 ,
1.18 christos 205: which uses UTC for modern timestamps and some other UT flavor for
206: timestamps that predate the introduction of UTC.
1.11 christos 207: No attempt is currently made to have the output use
208: .Dq UTC
209: for newer and
210: .Dq UT
1.18 christos 211: for older timestamps, partly because the exact date of the
1.15 christos 212: introduction of UTC is problematic.
1.4 wiz 213: .Sh SEE ALSO
214: .Xr tzfile 5 ,
215: .Xr zic 8
1.7 mlelstv 216: .\" @(#)zdump.8 8.2
217: .\" This file is in the public domain, so clarified as of
218: .\" 2009-05-17 by Arthur David Olson.
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