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Revision 1.22, Wed Apr 16 13:34:58 2003 UTC (18 years ago) by wiz
Use .In header.h instead of .Fd #include \*[Lt]header.h\*[Gt] Much easier to read and write, and supported by groff for ages. Okayed by ross.
.\" $NetBSD: tzset.3,v 1.22 2003/04/16 13:34:58 wiz Exp $ .Dd April 1, 2001 .Dt TZSET 3 .Os .Sh NAME .Nm tzset .Nd initialize time conversion information .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In time.h .Ft void .Fn tzset "void" .Sh DESCRIPTION The .Fn tzset function uses the value of the environment variable .Ev TZ to set time conversion information used by .Xr localtime 3 . If .Ev TZ does not appear in the environment, the best available approximation to local wall clock time, as specified by the .Xr tzfile 5 format file .Pa /etc/localtime is used by .Xr localtime 3 . If .Ev TZ appears in the environment but its value is a null string, Coordinated Universal Time (UTC) is used (without leap second correction). If .Ev TZ appears in the environment and its value is not a null string: .Bl -dash .It if the value begins with a colon, it is used as a pathname of a file from which to read the time conversion information; .It if the value does not begin with a colon, it is first used as the pathname of a file from which to read the time conversion information, and, if that file cannot be read, is used directly as a specification of the time conversion information. .El .Pp When .Ev TZ is used as a pathname, if it begins with a slash, it is used as an absolute pathname; otherwise, it is used as a pathname relative to .Pa /usr/share/zoneinfo . The file must be in the format specified in .Xr tzfile 5 . .Pp When .Ev TZ is used directly as a specification of the time conversion information, it must have the following syntax (spaces inserted for clarity): .Sm off .Bd -literal -offset indent .Cm std Cm offset Oo .Cm dst Oo .Cm offset Oc Oo .No , Cm rule Oc Oc .Ed .Sm on .Pp where: .Bl -tag -width "std and dst" -compact .It Cm std No and Cm dst Three or more bytes that are the designation for the standard .Cm ( std ) or summer .Cm ( dst ) time zone. Only .Cm std is required; if .Cm dst is missing, then summer time does not apply in this locale. Upper- and lowercase letters are explicitly allowed. Any characters except a leading colon (:), digits, comma (,), minus (-), plus (+), and ASCII NUL are allowed. .It Cm offset Indicates the value one must add to the local time to arrive at Coordinated Universal Time. The .Cm offset has the form: .Sm off .Bd -literal -offset indent .Cm hh Oo .Cm :mm Oo .Cm :ss Oc Oc .Ed .Sm on .Pp The minutes .Cm ( mm ) and seconds .Cm ( ss ) are optional. The hour .Cm ( hh ) is required and may be a single digit. The .Cm offset following .Cm std is required. If no .Cm offset follows .Cm dst , summer time is assumed to be one hour ahead of standard time. One or more digits may be used; the value is always interpreted as a decimal number. The hour must be between zero and 24, and the minutes (and seconds) \(em if present \(em between zero and 59. If preceded by a .Dq - the time zone shall be east of the Prime Meridian; otherwise it shall be west (which may be indicated by an optional preceding .Dq + ) . .It Cm rule Indicates when to change to and back from summer time. The .Cm rule has the form: .Sm off .Bd -literal -offset indent .Xo .Cm date No / .Cm time No , .Cm date No / .Cm time .Xc .Ed .Sm on .Pp where the first .Cm date describes when the change from standard to summer time occurs and the second .Cm date describes when the change back happens. Each .Cm time field describes when, in current local time, the change to the other time is made. .IP The format of .Fa date is one of the following: .Bl -tag -width "The Julian day" -compact .It Cm J Ns Ar n The Julian day .Ar n (1 \*[Le] .Ar n \*[Le] 365). Leap days are not counted; that is, in all years \(em including leap years \(em February 28 is day 59 and March 1 is day 60. It is impossible to explicitly refer to the occasional February 29. .It Ar n The zero-based Julian day (0\ \*[Le] .Ar n \*[Le]\ 365). Leap days are counted, and it is possible to refer to February 29. .Sm off .It Xo Cm M Ns Ar m .No . Ar n No . Ar d .Xc .Sm on The .Ar d Ns 'th day (0 \*[Le] .Ar d \*[Le]\ 6) of week .Ar n of month .Ar m of the year (1 \*[Le] .Ar n \*[Le]\ 5, 1 \*[Le] .Ar m \*[Le]\ 12, where week 5 means .Dq the\ last Ar d No day\ in\ month Ar m which may occur in either the fourth or the fifth week). Week 1 is the first week in which the .Ar d Ns 'th day occurs. Day zero is Sunday. .El The .Cm time has the same format as .Cm offset except that no leading sign .Dq - or .Dq + is allowed. The default, if .Cm time is not given, is .Cm 02:00:00 . .El If no .Cm rule is present in .Ev TZ , the rules specified by the .Xr tzfile 5 format file .Pa posixrules in .Pa /usr/share/zoneinfo are used, with the standard and summer time offsets from UTC replaced by those specified by the .Cm offset values in .Ev TZ . .Pp For compatibility with System V Release 3.1, a semicolon (;) may be used to separate the .Cm rule from the rest of the specification. .Pp If the .Ev TZ environment variable does not specify a .Xr tzfile 5 format file and cannot be interpreted as a direct specification, UTC is used. .Sh FILES .Bl -tag -width /usr/share/zoneinfo/posixrules -compact .It Pa /etc/localtime local time zone file .It Pa /usr/share/zoneinfo time zone information directory .It Pa /usr/share/zoneinfo/posixrules used with POSIX-style TZ's .It Pa /usr/share/zoneinfo/GMT for UTC leap seconds .El .Pp If .Pa /usr/share/zoneinfo/GMT is absent, UTC leap seconds are loaded from .Pa /usr/share/zoneinfo/posixrules . .Sh SEE ALSO .Xr ctime 3 , .Xr getenv 3 , .Xr strftime 3 , .Xr time 3 , .Xr tzfile 5 .Sh STANDARDS The tzset() function conforms to .St -p1003.1-88 . .\" @(#)newtzset.3 7.5