| 1 | .TH TZ 5
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| 2 | .SH NAME
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| 3 | TZ \- Time zone environment variable
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| 4 | .SH SYNOPSIS
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| 5 | \fBTZ=\fIzone\fR[\fB\-\fR]\fIoffset\fR[\fIdst\fR[\fIoffset\fR][\fB,\fIstart\fR[\fB/\fItime\fR]\fB,\fIend\fR[\fB/\fItime\fR]]]
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| 6 | .SH DESCRIPTION
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| 7 | .de SP
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| 8 | .if t .sp 0.4
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| 9 | .if n .sp
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| 10 | ..
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| 11 | The
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| 12 | .B TZ
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| 13 | environment variable tells functions such as the
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| 14 | .BR ctime (3)
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| 15 | family and programs like
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| 16 | .B date
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| 17 | what the time zone and daylight saving rule is. The value of
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| 18 | .B TZ
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| 19 | has the \s-2POSIX\s+2 standardized form shown in the synopsis. This form
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| 20 | specifies the zone names, offsets from GMT, and daylight saving changeover
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| 21 | times for at least the current year.
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| 22 | .TP
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| 23 | .I zone
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| 24 | A three or more letter name for the time zone in normal (winter) time.
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| 25 | .TP
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| 26 | .BI [\-] offset
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| 27 | A signed time telling the offset of the time zone westwards from Greenwich.
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| 28 | The time has the form
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| 29 | .I hh[:mm[:ss]]
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| 30 | with a one of two digit hour, and optional two digit minutes and seconds.
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| 31 | .TP
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| 32 | .I dst
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| 33 | The name of the time zone when daylight saving is in effect. It may
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| 34 | be followed by an offset telling how big the clock correction is other than
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| 35 | the default of 1 hour.
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| 36 | .TP
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| 37 | \fIstart\fR/\fItime\fR,\fIend\fR/\fItime\fR
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| 38 | Specifies the start and end of the daylight saving period. The
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| 39 | .I start
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| 40 | and
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| 41 | .I end
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| 42 | fields indicate on what day the changeover occurs. They must be in one of
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| 43 | the following formats:
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| 44 | .SP
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| 45 | .ta +5
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| 46 | .in +5
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| 47 | .ti -5
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| 48 | \fBJ\fIn\fR The Julian day
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| 49 | .I n
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| 50 | (1 <=
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| 51 | .I n
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| 52 | <= 365) ignoring leap days, i.e. there is no February 29.
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| 53 | .SP
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| 54 | .ti -5
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| 55 | \fIn\fR The zero-based Julian day
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| 56 | (0 <=
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| 57 | .I n
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| 58 | <= 365). Leap days are not ignored.
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| 59 | .SP
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| 60 | .ti -5
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| 61 | .BI M m . n . d
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| 62 | .br
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| 63 | This indicates month
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| 64 | .IR m ,
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| 65 | the
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| 66 | .IR n -th
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| 67 | occurrence of day
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| 68 | .I d
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| 69 | (1 <=
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| 70 | .I m
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| 71 | <= 12, 1 <=
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| 72 | .I n
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| 73 | <= 5, 0 <=
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| 74 | .I d
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| 75 | <= 6, 0=Sunday). The 5-th occurrence means the last occurrence of that day
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| 76 | in a month. So
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| 77 | .B M4.1.0
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| 78 | is the first Sunday in April,
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| 79 | .B M9.5.0
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| 80 | is the last Sunday in September.
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| 81 | .in -5
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| 82 | .SP
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| 83 | The
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| 84 | .I time
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| 85 | field indicates the time the changeover occurs on the given day.
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| 86 | .SH EXAMPLES
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| 87 | Greenwich Mean Time:
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| 88 | .PP
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| 89 | .RS
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| 90 | .B TZ=GMT0
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| 91 | .RE
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| 92 | .PP
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| 93 | Central European Time, 1 hour east from Greenwich, daylight saving starts on
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| 94 | the last Sunday in March at 2 AM and ends on the last Sunday in October
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| 95 | at 3 AM:
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| 96 | .PP
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| 97 | .RS
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| 98 | .B TZ='CET\-1CEST,M3.5.0/2,M10.5.0/3'
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| 99 | .RE
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| 100 | .PP
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| 101 | British time, daylight saving starts and ends at the same moment as CET,
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| 102 | but in an earlier time zone:
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| 103 | .PP
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| 104 | .RS
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| 105 | .B TZ=GMT0BST,M3.5.0/1,M10.5.0/2
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| 106 | .RE
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| 107 | .PP
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| 108 | The eastern european time zones also have the changeovers at the same
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| 109 | absolute time as British time and CET.
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| 110 | .PP
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| 111 | U.S. Eastern Standard Time, 5 hours west from Greenwich, daylight saving
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| 112 | starts on the first Sunday in April at 2 AM and ends on the last Sunday in
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| 113 | October at 2 AM:
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| 114 | .PP
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| 115 | .RS
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| 116 | .B TZ=EST5EDT,M4.1.0/2,M10.5.0/2
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| 117 | .RE
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| 118 | .PP
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| 119 | It shouldn't surprise you that daylight saving in New Zealand is observed
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| 120 | in the months opposite from the previous examples. It starts on the first
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| 121 | Sunday in October at 2 AM and ends on the third Sunday in March at 3 AM:
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| 122 | .PP
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| 123 | .RS
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| 124 | .B TZ=NZST\-12NZDT,M10.1.0/2,M3.3.0/3
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| 125 | .RE
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| 126 | .SH "SEE ALSO"
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| 127 | .BR readclock (8),
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| 128 | .BR date (1).
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| 129 | .SH BUGS
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| 130 | You may have noticed that many fields are optional. Do no omit them,
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| 131 | because the defaults are bogus. If you need daylight saving then fully
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| 132 | specify the changeovers.
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| 133 | .PP
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| 134 | West is negative, east is positive, ask any sailor.
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| 135 | .PP
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| 136 | Next year's time zone and daylight saving time are determined by politicians.
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| 137 | .SH AUTHOR
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| 138 | Kees J. Bot (kjb@cs.vu.nl)
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