104 lines
2.8 KiB
Groff
104 lines
2.8 KiB
Groff
.\" $NetBSD: zdump.8,v 1.14 2014/10/23 18:45:58 christos Exp $
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.Dd October 23, 2014
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.Dt ZDUMP 8
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.Os
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.Sh NAME
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.Nm zdump
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.Nd time zone dumper
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.Sh SYNOPSIS
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.Nm zdump
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.Op Fl \-version
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.Op Fl v
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.Op Fl V
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.Op Fl c Ar [loyear,]highyear
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.Op Ar zonename ...
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.Nm zdump
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.Fl t
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.Ar [lotime,]hightime
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.Op Ar zonename ...
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.Sh DESCRIPTION
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.Nm
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prints the current time in each
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.Ar zonename
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named on the command line.
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.Pp
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These options are available:
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.Bl -tag -width XXXXXXXXX -compact
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.It Fl \-version
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Output version information and exit.
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.It Fl v
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For each
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.Ar zonename
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on the command line,
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print the time at the lowest possible time value,
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the time one day after the lowest possible time value,
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the times both one second before and exactly at
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each detected time discontinuity,
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the time at one day less than the highest possible time value,
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and the time at the highest possible time value.
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Each line is followed by
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.Dl isdst= D
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where
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.Dl D
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is positive, zero, or negative depending on whether
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the given time is daylight saving time, standard time,
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or an unknown time type, respectively.
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Each line is also followed by
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.Dl gmtoff= N
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if the given local time is known to be
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.D N
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seconds east of Greenwich.
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.It Fl c Ar [loyear,]highyear
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Cut off verbose output at the given year(s).
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Cutoff times are computed using the proleptic Gregorian calendar with year 0
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and with Universal Time (UT) ignoring leap seconds.
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The lower bound is exclusive and the upper is inclusive; for example, a
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.Dl loyear
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of 1970 excludes a transition occurring at 1970-01-01 00:00:00 UTC but a
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.Dl hiyear
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of 1970 includes the transition.
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The default cutoff is
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.Dl \*-500,2500 .
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.It Fl t Ar [lotime,]hightime
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Cut off verbose output at the given time(s),
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given in decimal seconds since 1970-01-01 00:00:00
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Coordinated Universal Time (UTC).
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The
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.Ar zonename
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determines whether the count includes leap seconds.
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As with
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.Fl c ,
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the cutoff's lower bound is exclusive and its upper bound is inclusive.
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.It Fl V
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Like
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.Fl v ,
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except omit the times relative to the extreme time values.
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This generates output that is easier to compare to that of
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implementations with different time representations.
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.El
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.Sh LIMITATIONS
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Time discontinuities are found by sampling the results returned by localtime
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at twelve-hour intervals.
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This works in all real-world cases;
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one can construct artificial time zones for which this fails.
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.Pp
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In the output,
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.Dq UT
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denotes the value returned by
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.Xr gmtime 3 ,
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which uses UTC for modern time stamps and some other UT flavor for
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time stamps that predate the introduction of UTC.
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No attempt is currently made to have the output use
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.Dq UTC
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for newer and
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.Dq UT
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for older time stamps,
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partly because the exact date of the introduction of UTC is problematic.
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.Sh SEE ALSO
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.Xr ctime 3 ,
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.Xr tzfile 5 ,
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.Xr zic 8
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.\" @(#)zdump.8 8.2
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.\" This file is in the public domain, so clarified as of
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.\" 2009-05-17 by Arthur David Olson.
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