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31 .\" @(#)tzset.3 8.2 (Berkeley) 11/17/93
39 .Nd initialize time conversion information
50 initializes time conversion information used by the library routine
52 The environment variable
54 specifies how this is done.
58 does not appear in the environment, the best available approximation to
59 local wall clock time, as specified by the
60 .Xr tzfile 5 Ns -format
67 appears in the environment but its value is a null string, Coordinated
70 is used (without leap second correction).
74 appears in the environment and its value begins with a colon
76 the rest of its value is used as a pathname of a
77 .Xr tzfile 5 Ns -format
78 file from which to read the time conversion information.
79 If the first character of the pathname is a slash
82 an absolute pathname; otherwise, it is used as a pathname relative to
83 the system time conversion information directory.
85 If its value does not begin with a colon, it is first used as the pathname
86 of a file (as described above) from which to read the time conversion
88 If that file cannot be read, the value is then interpreted as a direct
89 specification (the format is described below) of the time conversion
94 environment variable does not specify a
95 .Xr tzfile 5 Ns -format
96 file and cannot be interpreted as a direct specification,
99 .Sh SPECIFICATION FORMAT
102 is used directly as a specification of the time conversion information,
103 it must have the following syntax (spaces inserted for clarity):
104 .Bd -ragged -offset indent
114 .Bl -tag -width std_and_dst -offset indent
115 .It Em std No and Em dst
116 Three or more bytes that are the designation for the standard
125 is missing, then summer time does not apply in this locale.
126 Upper and lowercase letters are explicitly allowed.
128 except a leading colon
141 Indicates the value one must add to the local time to arrive at
142 Coordinated Universal Time.
146 .Bd -ragged -offset indent
162 is required and may be a single digit.
172 summer time is assumed to be one hour ahead of standard time.
174 more digits may be used; the value is always interpreted as a decimal
176 The hour must be between zero and 24, and the minutes (and
177 seconds) \(em if present \(em between zero and 59.
180 the time zone shall be east of the Prime Meridian; otherwise it shall be
181 west (which may be indicated by an optional preceding
184 Indicates when to change to and back from summer time.
188 .Bd -ragged -offset indent
189 .Em date/time,date/time
194 describes when the change from standard to summer time occurs and the
197 describes when the change back happens.
200 field describes when, in current local time, the change to the other
205 is one of the following:
206 .Bl -tag -width "M.m.n.d"
213 Leap days are not counted; that is, in all years \(em including leap
214 years \(em February 28 is day 59 and March 1 is day 60.
216 impossible to explicitly refer to the occasional February 29.
218 The zero-based Julian day
222 Leap days are counted, and it is possible to refer to February 29.
247 which may occur in either the fourth or the fifth week).
249 first week in which the
256 has the same format as
258 except that no leading sign
273 specification, the rules specified
275 .Xr tzfile 5 Ns -format
278 in the system time conversion information directory are used, with the
279 standard and summer time offsets from
281 replaced by those specified by
288 For compatibility with System V Release 3.1, a semicolon
290 may be used to separate the
292 from the rest of the specification.
294 .Bl -tag -width /usr/share/zoneinfo/posixrules -compact
295 .It Pa /etc/localtime
297 .It Pa /usr/share/zoneinfo
299 .It Pa /usr/share/zoneinfo/posixrules
303 .It Pa /usr/share/zoneinfo/Etc/GMT
310 .Pa /usr/share/zoneinfo/UTC
313 leap seconds are loaded from
314 .Pa /usr/share/zoneinfo/posixrules .
325 function first appeared in