| blob | 7751858bc5a05a26c29019ab46840375e576c116 |
1 .TH TZ 5
2 .SH NAME
3 TZ \- Time zone environment variable
4 .SH SYNOPSIS
5 \fBTZ=\fIzone\fR[\fB\-\fR]\fIoffset\fR[\fIdst\fR[\fIoffset\fR][\fB,\fIstart\fR[\fB/\fItime\fR]\fB,\fIend\fR[\fB/\fItime\fR]]]
6 .SH DESCRIPTION
7 .de SP
8 .if t .sp 0.4
9 .if n .sp
10 ..
11 The
12 .B TZ
13 environment variable tells functions such as the
14 .BR ctime (3)
15 family and programs like
16 .B date
17 what the time zone and daylight saving rule is. The value of
18 .B TZ
19 has the \s-2POSIX\s+2 standardized form shown in the synopsis. This form
20 specifies the zone names, offsets from GMT, and daylight saving changeover
21 times for at least the current year.
22 .TP
23 .I zone
24 A three or more letter name for the time zone in normal (winter) time.
25 .TP
26 .BI [\-] offset
27 A signed time telling the offset of the time zone westwards from Greenwich.
28 The time has the form
29 .I hh[:mm[:ss]]
30 with a one or two digit hour, and optional two digit minutes and seconds.
31 .TP
32 .I dst
33 The name of the time zone when daylight saving is in effect. It may
34 be followed by an offset telling how big the clock correction is other than
35 the default of 1 hour.
36 .TP
37 \fIstart\fR/\fItime\fR,\fIend\fR/\fItime\fR
38 Specifies the start and end of the daylight saving period. The
39 .I start
40 and
41 .I end
42 fields indicate on what day the changeover occurs. They must be in one of
43 the following formats:
44 .SP
45 .ta +5
46 .in +5
47 .ti -5
48 \fBJ\fIn\fR The Julian day
49 .I n
50 (1 <=
51 .I n
52 <= 365) ignoring leap days, i.e. there is no February 29.
53 .SP
54 .ti -5
55 \fIn\fR The zero-based Julian day
56 (0 <=
57 .I n
58 <= 365). Leap days are not ignored.
59 .SP
60 .ti -5
61 .BI M m . n . d
62 .br
63 This indicates month
64 .IR m ,
65 the
66 .IR n -th
67 occurrence of day
68 .I d
69 (1 <=
70 .I m
71 <= 12, 1 <=
72 .I n
73 <= 5, 0 <=
74 .I d
75 <= 6, 0=Sunday). The 5-th occurrence means the last occurrence of that day
76 in a month. So
77 .B M4.1.0
78 is the first Sunday in April,
79 .B M9.5.0
80 is the last Sunday in September.
81 .in -5
82 .SP
83 The
84 .I time
85 field indicates the time the changeover occurs on the given day.
86 .SH EXAMPLES
87 Greenwich Mean Time:
88 .PP
89 .RS
90 .B TZ='GMT0'
91 .RE
92 .PP
93 Central European Time, 1 hour east from Greenwich, daylight saving starts on
94 the last Sunday in March at 2 AM and ends on the last Sunday in October
95 at 3 AM:
96 .PP
97 .RS
98 .B TZ='CET\-1CEST,M3.5.0/2,M10.5.0/3'
99 .RE
100 .PP
101 British time, daylight saving starts and ends at the same moment as CET,
102 but in an earlier time zone:
103 .PP
104 .RS
105 .B TZ='GMT0BST,M3.5.0/1,M10.5.0/2'
106 .RE
107 .PP
108 The eastern european time zones also have the changeovers at the same
109 absolute time as British time and CET.
110 .PP
111 U.S. Eastern Standard Time, 5 hours west from Greenwich, daylight saving
112 starts on the second Sunday in March at 2 AM and ends on the first Sunday in
113 November at 2 AM:
114 .PP
115 .RS
116 .B TZ='EST5EDT,M3.2.0/2,M11.1.0/2'
117 .RE
118 .PP
119 It shouldn't surprise you that daylight saving in New Zealand is observed
120 in the months opposite from the previous examples. It starts on the first
121 Sunday in October at 2 AM and ends on the third Sunday in March at 3 AM:
122 .PP
123 .RS
124 .B TZ='NZST\-12NZDT,M10.1.0/2,M3.3.0/3'
125 .RE
126 .SH "SEE ALSO"
127 .BR readclock (8),
128 .BR date (1).
129 .SH BUGS
130 You may have noticed that many fields are optional. Do not omit them,
131 because the defaults are bogus. If you need daylight saving then fully
132 specify the changeovers.
133 .PP
134 West is negative, east is positive, ask any sailor.
135 .PP
136 Next year's time zone and daylight saving time are determined by politicians.
137 .SH AUTHOR
138 Kees J. Bot (kjb@cs.vu.nl)
140 .\" corrected for US/Canada 2007 changes by ASW 2007-02-20