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35 .\" @(#)tzset.3 8.2 (Berkeley) 11/17/93
44 .Nd initialize time conversion information
57 initializes time conversion information used by the library routine
59 The environment variable
61 specifies how this is done.
65 does not appear in the environment, the best available approximation to
66 local wall clock time, as specified by the
67 .Xr tzfile 5 Ns -format
74 appears in the environment but its value is a null string, Coordinated
77 is used (without leap second correction).
81 appears in the environment and its value begins with a colon
83 the rest of its value is used as a pathname of a
84 .Xr tzfile 5 Ns -format
85 file from which to read the time conversion information.
86 If the first character of the pathname is a slash
89 an absolute pathname; otherwise, it is used as a pathname relative to
90 the system time conversion information directory.
92 If its value does not begin with a colon, it is first used as the pathname
93 of a file (as described above) from which to read the time conversion
95 If that file cannot be read, the value is then interpreted as a direct
96 specification (the format is described below) of the time conversion
101 environment variable does not specify a
102 .Xr tzfile 5 Ns -format
103 file and cannot be interpreted as a direct specification,
110 sets things up so that
112 returns the best available approximation of local wall clock time.
113 .Sh SPECIFICATION FORMAT
116 is used directly as a specification of the time conversion information,
117 it must have the following syntax (spaces inserted for clarity):
118 .Bd -ragged -offset indent
128 .Bl -tag -width std_and_dst -offset indent
129 .It Em std No and Em dst
130 Three or more bytes that are the designation for the standard
139 is missing, then summer time does not apply in this locale.
140 Upper and lowercase letters are explicitly allowed.
142 except a leading colon
155 Indicates the value one must add to the local time to arrive at
156 Coordinated Universal Time.
160 .Bd -ragged -offset indent
176 is required and may be a single digit.
186 summer time is assumed to be one hour ahead of standard time.
188 more digits may be used; the value is always interpreted as a decimal
190 The hour must be between zero and 24, and the minutes (and
191 seconds) \(em if present \(em between zero and 59.
194 the time zone shall be east of the Prime Meridian; otherwise it shall be
195 west (which may be indicated by an optional preceding
198 Indicates when to change to and back from summer time.
202 .Bd -ragged -offset indent
203 .Em date/time,date/time
208 describes when the change from standard to summer time occurs and the
211 describes when the change back happens.
214 field describes when, in current local time, the change to the other
219 is one of the following:
220 .Bl -tag -width "M.m.n.d"
227 Leap days are not counted; that is, in all years \(em including leap
228 years \(em February 28 is day 59 and March 1 is day 60.
230 impossible to explicitly refer to the occasional February 29.
232 The zero-based Julian day
236 Leap days are counted, and it is possible to refer to February 29.
261 which may occur in either the fourth or the fifth week).
263 first week in which the
270 has the same format as
272 except that no leading sign
287 specification, the rules specified
289 .Xr tzfile 5 Ns -format
292 in the system time conversion information directory are used, with the
293 standard and summer time offsets from
295 replaced by those specified by
302 For compatibility with System V Release 3.1, a semicolon
304 may be used to separate the
306 from the rest of the specification.
308 .Bl -tag -width /usr/share/zoneinfo/posixrules -compact
309 .It Pa /etc/localtime
311 .It Pa /usr/share/zoneinfo
313 .It Pa /usr/share/zoneinfo/posixrules
317 .It Pa /usr/share/zoneinfo/GMT
324 .Pa /usr/share/zoneinfo/GMT
327 leap seconds are loaded from
328 .Pa /usr/share/zoneinfo/posixrules .
341 functions first appeared in