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31 .\" @(#)tzset.3 8.2 (Berkeley) 11/17/93
38 .Nd initialize time conversion information
49 initializes time conversion information used by the library routine
51 The environment variable
53 specifies how this is done.
57 does not appear in the environment, the best available approximation to
58 local wall clock time, as specified by the
59 .Xr tzfile 5 Ns -format
66 appears in the environment but its value is a null string, Coordinated
69 is used (without leap second correction).
73 appears in the environment and its value begins with a colon
75 the rest of its value is used as a pathname of a
76 .Xr tzfile 5 Ns -format
77 file from which to read the time conversion information.
78 If the first character of the pathname is a slash
81 an absolute pathname; otherwise, it is used as a pathname relative to
82 the system time conversion information directory.
84 If its value does not begin with a colon, it is first used as the pathname
85 of a file (as described above) from which to read the time conversion
87 If that file cannot be read, the value is then interpreted as a direct
88 specification (the format is described below) of the time conversion
93 environment variable does not specify a
94 .Xr tzfile 5 Ns -format
95 file and cannot be interpreted as a direct specification,
98 .Sh SPECIFICATION FORMAT
101 is used directly as a specification of the time conversion information,
102 it must have the following syntax (spaces inserted for clarity):
103 .Bd -ragged -offset indent
113 .Bl -tag -width std_and_dst -offset indent
114 .It Em std No and Em dst
115 Three or more bytes that are the designation for the standard
124 is missing, then summer time does not apply in this locale.
125 Upper and lowercase letters are explicitly allowed.
127 except a leading colon
140 Indicates the value one must add to the local time to arrive at
141 Coordinated Universal Time.
145 .Bd -ragged -offset indent
161 is required and may be a single digit.
171 summer time is assumed to be one hour ahead of standard time.
173 more digits may be used; the value is always interpreted as a decimal
175 The hour must be between zero and 24, and the minutes (and
176 seconds) \(em if present \(em between zero and 59.
179 the time zone shall be east of the Prime Meridian; otherwise it shall be
180 west (which may be indicated by an optional preceding
183 Indicates when to change to and back from summer time.
187 .Bd -ragged -offset indent
188 .Em date/time,date/time
193 describes when the change from standard to summer time occurs and the
196 describes when the change back happens.
199 field describes when, in current local time, the change to the other
204 is one of the following:
205 .Bl -tag -width "M.m.n.d"
212 Leap days are not counted; that is, in all years \(em including leap
213 years \(em February 28 is day 59 and March 1 is day 60.
215 impossible to explicitly refer to the occasional February 29.
217 The zero-based Julian day
221 Leap days are counted, and it is possible to refer to February 29.
246 which may occur in either the fourth or the fifth week).
248 first week in which the
255 has the same format as
257 except that no leading sign
272 specification, the rules specified
274 .Xr tzfile 5 Ns -format
277 in the system time conversion information directory are used, with the
278 standard and summer time offsets from
280 replaced by those specified by
287 For compatibility with System V Release 3.1, a semicolon
289 may be used to separate the
291 from the rest of the specification.
293 .Bl -tag -width /usr/share/zoneinfo/posixrules -compact
294 .It Pa /etc/localtime
296 .It Pa /usr/share/zoneinfo
298 .It Pa /usr/share/zoneinfo/posixrules
302 .It Pa /usr/share/zoneinfo/Etc/GMT
309 .Pa /usr/share/zoneinfo/UTC
312 leap seconds are loaded from
313 .Pa /usr/share/zoneinfo/posixrules .
324 function first appeared in