154 lines
6.7 KiB
Text
154 lines
6.7 KiB
Text
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NAME
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tzset - initialize time conversion information
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SYNOPSIS
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void tzset()
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cc ... -ltz
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DESCRIPTION
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Tzset uses the value of the environment variable TZ to set
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time conversion information used by localtime. If TZ does
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not appear in the environment, the best available
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approximation to local wall clock time, as specified by the
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tzfile(5)-format file localtime in the system time
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conversion information directory, is used by localtime. If
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TZ appears in the environment but its value is a null
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string, Coordinated Universal Time (UTC) is used (without
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leap second correction). If TZ appears in the environment
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and its value is not a null string:
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if the value begins with a colon, it is used as a
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pathname of a file from which to read the time
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conversion information;
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if the value does not begin with a colon, it is first
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used as the pathname of a file from which to read the
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time conversion information, and, if that file cannot
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be read, is used directly as a specification of the
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time conversion information.
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When TZ is used as a pathname, if it begins with a slash, it
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is used as an absolute pathname; otherwise, it is used as a
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pathname relative to a system time conversion information
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directory. The file must be in the format specified in
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tzfile(5).
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When TZ is used directly as a specification of the time
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conversion information, it must have the following syntax
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(spaces inserted for clarity):
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stdoffset[dst[offset][,rule]]
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Where:
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std and dst Three or more bytes that are the
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designation for the standard (std) or
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summer (dst) time zone. Only std is
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required; if dst is missing, then summer
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time does not apply in this locale.
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Upper- and lowercase letters are
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explicitly allowed. Any characters
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except a leading colon (:), digits,
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comma (,), minus (-), plus (+), and
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ASCII NUL are allowed.
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offset Indicates the value one must add to the
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local time to arrive at Coordinated
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Universal Time. The offset has the
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form:
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hh[:mm[:ss]]
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The minutes (mm) and seconds (ss) are
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optional. The hour (hh) is required and
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may be a single digit. The offset
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following std is required. If no offset
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follows dst, summer time is assumed to
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be one hour ahead of standard time. One
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or more digits may be used; the value is
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always interpreted as a decimal number.
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The hour must be between zero and 24,
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and the minutes (and seconds) - if
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present - between zero and 59. If
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preceded by a ``-'', the time zone shall
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be east of the Prime Meridian; otherwise
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it shall be west (which may be indicated
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by an optional preceding ``+'').
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rule Indicates when to change to and back
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from summer time. The rule has the
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form:
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date/time,date/time
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where the first date describes when the
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change from standard to summer time
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occurs and the second date describes
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when the change back happens. Each time
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field describes when, in current local
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time, the change to the other time is
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made.
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The format of date is one of the
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following:
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Jn The Julian day n
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(1 < n < 365). Leap days are
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not counted; that is, in all
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years - including leap years -
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February 28 is day 59 and
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March 1 is day 60. It is
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impossible to explicitly refer
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to the occasional February 29.
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n The zero-based Julian day
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(0 < n < 365). Leap days are
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counted, and it is possible to
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refer to February 29.
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Mm.n.d The d'th day (0 < d < 6) of
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week n of month m of the year
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(1 < n < 5, 1 < m < 12, where
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week 5 means ``the last d day
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in month m'' which may occur
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in either the fourth or the
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fifth week). Week 1 is the
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first week in which the d'th
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day occurs. Day zero is
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Sunday.
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The time has the same format as offset
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except that no leading sign (``-'' or
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``+'') is allowed. The default, if time
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is not given, is 02:00:00.
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If no rule is present in TZ, the rules specified by the
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tzfile(5)-format file posixrules in the system time
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conversion information directory are used, with the standard
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and summer time offsets from UTC replaced by those specified
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by the offset values in TZ.
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For compatibility with System V Release 3.1, a semicolon (;)
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may be used to separate the rule from the rest of the
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specification.
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If the TZ environment variable does not specify a
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tzfile(5)-format and cannot be interpreted as a direct
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specification, UTC is used.
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FILES
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/usr/local/etc/zoneinfo time zone information
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directory
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/usr/local/etc/zoneinfo/localtime local time zone file
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/usr/local/etc/zoneinfo/posixrules used with POSIX-style
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TZ's
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/usr/local/etc/zoneinfo/GMT for UTC leap seconds
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If /usr/local/etc/zoneinfo/GMT is absent, UTC leap seconds
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are loaded from /usr/local/etc/zoneinfo/posixrules.
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SEE ALSO
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getenv(3), newctime(3), newstrftime(3), time(2), tzfile(5)
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