138 lines
3.3 KiB
Groff
138 lines
3.3 KiB
Groff
.TH TZ 5
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.SH NAME
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TZ \- Time zone environment variable
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.SH SYNOPSIS
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\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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.SH DESCRIPTION
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.de SP
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.if t .sp 0.4
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.if n .sp
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..
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The
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.B TZ
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environment variable tells functions such as the
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.BR ctime (3)
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family and programs like
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.B date
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what the time zone and daylight saving rule is. The value of
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.B TZ
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has the \s-2POSIX\s+2 standardized form shown in the synopsis. This form
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specifies the zone names, offsets from GMT, and daylight saving changeover
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times for at least the current year.
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.TP
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.I zone
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A three or more letter name for the time zone in normal (winter) time.
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.TP
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.BI [\-] offset
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A signed time telling the offset of the time zone westwards from Greenwich.
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The time has the form
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.I hh[:mm[:ss]]
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with a one of two digit hour, and optional two digit minutes and seconds.
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.TP
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.I dst
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The name of the time zone when daylight saving is in effect. It may
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be followed by an offset telling how big the clock correction is other than
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the default of 1 hour.
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.TP
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\fIstart\fR/\fItime\fR,\fIend\fR/\fItime\fR
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Specifies the start and end of the daylight saving period. The
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.I start
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and
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.I end
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fields indicate on what day the changeover occurs. They must be in one of
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the following formats:
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.SP
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.ta +5
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.in +5
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.ti -5
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\fBJ\fIn\fR The Julian day
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.I n
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(1 <=
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.I n
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<= 365) ignoring leap days, i.e. there is no February 29.
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.SP
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.ti -5
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\fIn\fR The zero-based Julian day
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(0 <=
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.I n
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<= 365). Leap days are not ignored.
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.SP
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.ti -5
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.BI M m . n . d
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.br
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This indicates month
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.IR m ,
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the
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.IR n -th
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occurrence of day
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.I d
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(1 <=
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.I m
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<= 12, 1 <=
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.I n
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<= 5, 0 <=
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.I d
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<= 6, 0=Sunday). The 5-th occurrence means the last occurrence of that day
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in a month. So
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.B M4.1.0
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is the first Sunday in April,
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.B M9.5.0
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is the last Sunday in September.
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.in -5
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.SP
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The
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.I time
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field indicates the time the changeover occurs on the given day.
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.SH EXAMPLES
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Greenwich Mean Time:
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.PP
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.RS
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.B TZ=GMT0
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.RE
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.PP
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Central European Time, 1 hour east from Greenwich, daylight saving starts on
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the last Sunday in March at 2 AM and ends on the last Sunday in October
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at 3 AM:
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.PP
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.RS
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.B TZ='CET\-1CEST,M3.5.0/2,M10.5.0/3'
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.RE
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.PP
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British time, daylight saving starts and ends at the same moment as CET,
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but in an earlier time zone:
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.PP
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.RS
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.B TZ=GMT0BST,M3.5.0/1,M10.5.0/2
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.RE
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.PP
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The eastern european time zones also have the changeovers at the same
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absolute time as British time and CET.
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.PP
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U.S. Eastern Standard Time, 5 hours west from Greenwich, daylight saving
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starts on the second Sunday in March at 2 AM and ends on the first Sunday
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in November at 2 AM:
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.PP
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.RS
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.B TZ=EST5EDT,M3.2.0/2,M11.1.0/2
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.RE
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.PP
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It shouldn't surprise you that daylight saving in New Zealand is observed
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in the months opposite from the previous examples. It starts on the first
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Sunday in October at 2 AM and ends on the third Sunday in March at 3 AM:
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.PP
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.RS
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.B TZ=NZST\-12NZDT,M10.1.0/2,M3.3.0/3
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.RE
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.SH "SEE ALSO"
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.BR readclock (8),
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.BR date (1).
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.SH BUGS
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You may have noticed that many fields are optional. Do not omit them,
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because the defaults are bogus. If you need daylight saving then fully
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specify the changeovers.
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.PP
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West is negative, east is positive, ask any sailor.
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.PP
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Next year's time zone and daylight saving time are determined by politicians.
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.SH AUTHOR
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Kees J. Bot (kjb@cs.vu.nl)
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