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35 .\" $FreeBSD: src/lib/libc/gen/tzset.3,v 1.6.2.5 2001/12/14 18:33:51 ru Exp $
43 .Nd initialize time conversion information
56 initializes time conversion information used by the library routine
58 The environment variable
60 specifies how this is done.
64 does not appear in the environment, the best available approximation to
65 local wall clock time, as specified by the
66 .Xr tzfile 5 Ns -format
73 appears in the environment but its value is a null string, Coordinated
76 is used (without leap second correction).
80 appears in the environment and its value begins with a colon
82 the rest of its value is used as a pathname of a
83 .Xr tzfile 5 Ns -format
84 file from which to read the time conversion information.
85 If the first character of the pathname is a slash
88 an absolute pathname; otherwise, it is used as a pathname relative to
89 the system time conversion information directory.
91 If its value does not begin with a colon, it is first used as the pathname
92 of a file (as described above) from which to read the time conversion
94 If that file cannot be read, the value is then interpreted as a direct
95 specification (the format is described below) of the time conversion
100 environment variable does not specify a
101 .Xr tzfile 5 Ns -format
102 file and cannot be interpreted as a direct specification,
109 sets things up so that
111 returns the best available approximation of local wall clock time.
112 .Sh SPECIFICATION FORMAT
115 is used directly as a specification of the time conversion information,
116 it must have the following syntax (spaces inserted for clarity):
117 .Bd -ragged -offset indent
127 .Bl -tag -width std_and_dst -offset indent
128 .It Em std No and Em dst
129 Three or more bytes that are the designation for the standard
137 is missing, then summer time does not apply in this locale.
138 Upper and lowercase letters are explicitly allowed. Any characters
139 except a leading colon
152 Indicates the value one must add to the local time to arrive at
153 Coordinated Universal Time. The
156 .Bd -ragged -offset indent
169 are optional. The hour
171 is required and may be a single digit. The
179 summer time is assumed to be one hour ahead of standard time. One or
180 more digits may be used; the value is always interpreted as a decimal
181 number. The hour must be between zero and 24, and the minutes (and
182 seconds) \(em if present \(em between zero and 59. If preceded by a
184 the time zone shall be east of the Prime Meridian; otherwise it shall be
185 west (which may be indicated by an optional preceding
188 Indicates when to change to and back from summer time. The
191 .Bd -ragged -offset indent
192 .Em date/time,date/time
197 describes when the change from standard to summer time occurs and the
200 describes when the change back happens. Each
202 field describes when, in current local time, the change to the other
207 is one of the following:
208 .Bl -tag -width "M.m.n.d"
215 Leap days are not counted; that is, in all years \(em including leap
216 years \(em February 28 is day 59 and March 1 is day 60. It is
217 impossible to explicitly refer to the occasional February 29.
219 The zero-based Julian day
223 Leap days are counted, and it is possible to refer to February 29.
248 which may occur in either the fourth or the fifth week). Week 1 is the
249 first week in which the
251 day occurs. Day zero is Sunday.
255 has the same format as
257 except that no leading sign
261 is allowed. The default, if
271 specification, the rules specified
273 .Xr tzfile 5 Ns -format
276 in the system time conversion information directory are used, with the
277 standard and summer time offsets from
279 replaced by those specified by
286 For compatibility with System V Release 3.1, a semicolon
288 may be used to separate the
290 from the rest of the specification.
292 .Bl -tag -width /usr/share/zoneinfo/posixrules -compact
293 .It Pa /etc/localtime
295 .It Pa /usr/share/zoneinfo
297 .It Pa /usr/share/zoneinfo/posixrules
301 .It Pa /usr/share/zoneinfo/GMT
308 .Pa /usr/share/zoneinfo/GMT
311 leap seconds are loaded from
312 .Pa /usr/share/zoneinfo/posixrules .
326 functions first appeared in