.\"	$OpenBSD: zic.8,v 1.6 2024/09/18 17:05:50 millert Exp $
.Dd $Mdocdate: September 18 2024 $
.Dt ZIC 8
.Os
.Sh NAME
.Nm zic
.Nd time zone compiler
.Sh SYNOPSIS
.Nm zic
.Bk -words
.Op Fl v
.Op Fl d Ar directory
.Op Fl L Ar leapsecondfilename
.Op Fl l Ar timezone
.Op Fl p Ar timezone
.Op Ar filename ...
.Ek
.Sh DESCRIPTION
.Nm
reads text from the file(s) named on the command line
and creates the time conversion information files specified in this input.
If a
.Ar filename
is
.Dq Fl ,
the standard input is read.
.Pp
These options are available:
.Bl -tag -width "-d directory"
.It Fl d Ar directory
Create time conversion information files in the named directory rather than
in the standard directory named below.
.It Fl L Ar leapsecondfilename
Read leap second information from the file with the given name.
If this option is not used,
no leap second information appears in output files.
.It Fl l Ar timezone
Use the given time zone as local time.
.Nm
will act as if the input contained a link line of the form
.Pp
.Dl Link	timezone		localtime
.It Fl p Ar timezone
Use the given time zone's rules when handling POSIX-format
time zone environment variables.
.Nm
will act as if the input contained a link line of the form
.Pp
.Dl Link	timezone		posixrules
.It Fl v
Complain if a year that appears in a data file is outside the range
of years representable by
.Xr time 3
values.
Also complain if a time of 24:00
(which cannot be handled by pre-1998 versions of
.Nm zic )
appears in the input.
.El
.Pp
Input lines are made up of fields.
Fields are separated from one another by any number of whitespace characters.
Leading and trailing whitespace on input lines is ignored.
An unquoted sharp character (#) in the input introduces a comment which extends
to the end of the line the sharp character appears on.
White space characters and sharp characters may be enclosed in double quotes
(") if they're to be used as part of a field.
Any line that is blank (after comment stripping) is ignored.
Non-blank lines are expected to be of one of three types:
rule lines, zone lines, and link lines.
.Pp
Names (such as month names) must be in English and are case insensitive.
Abbreviations, if used, must be unambiguous in context.
.Pp
A rule line has the form:
.Bd -literal -offset indent
Rule  NAME  FROM  TO    TYPE  IN    ON       AT    SAVE  LETTER/S
.Ed
.Pp
For example:
.Bd -literal -offset indent
Rule  US    1967  1973  -     Apr   lastSun  2:00  1:00  D
.Ed
.Pp
The fields that make up a rule line are:
.Bl -tag -width "LETTER/S"
.It Cm NAME
Gives the (arbitrary) name of the set of rules this rule is part of.
.It Cm FROM
Gives the first year in which the rule applies.
Any integer year can be supplied; the Gregorian calendar is assumed.
The word
.Em minimum
(or an abbreviation) means the minimum year representable as an integer.
The word
.Em maximum
(or an abbreviation) means the maximum year representable as an integer.
Rules can describe times that are not representable as time values,
with the unrepresentable times ignored; this allows rules to be portable
among hosts with differing time value types.
.It Cm TO
Gives the final year in which the rule applies.
In addition to
.Em minimum
and
.Em maximum
(as above),
the word
.Em only
(or an abbreviation)
may be used to repeat the value of the
.Em FROM
field.
.It Cm TYPE
Gives the type of year in which the rule applies.
This field is obsolete and should always be
.Dq Fl .
.It Cm IN
Names the month in which the rule takes effect.
Month names may be abbreviated.
.It Cm ON
Gives the day on which the rule takes effect.
Recognized forms include:
.Pp
.Bl -tag -width "SunXX25" -compact -offset indent
.It 5
the fifth of the month
.It lastSun
the last Sunday in the month
.It lastMon
the last Monday in the month
.It Sun>=8
first Sunday on or after the eighth
.It Sun<=25
last Sunday on or before the 25th
.El
.Pp
Names of days of the week may be abbreviated or spelled out in full.
Note that there must be no spaces within the
.Em ON
field.
.It Cm AT
Gives the time of day at which the rule takes effect.
Recognized forms include:
.Pp
.Bl -tag -width "1:28:14" -compact -offset indent
.It 2
time in hours
.It 2:00
time in hours and minutes
.It 15:00
24-hour format time (for times after noon)
.It 1:28:14
time in hours, minutes, and seconds
.It \&-
equivalent to 0
.El
.Pp
where hour 0 is midnight at the start of the day,
and hour 24 is midnight at the end of the day.
Any of these forms may be followed by the letter
.Em w
if the given time is local
.Dq wall clock
time,
.Em s
if the given time is local
.Dq standard
time, or
.Em u
(or
.Em g
or
.Em z )
if the given time is universal time;
in the absence of an indicator,
wall clock time is assumed.
.It Cm SAVE
Gives the amount of time to be added to local standard time when the rule is in
effect.
This field has the same format as the
.Em AT
field
(although, of course, the
.Em w
and
.Em s
suffixes are not used).
.It Cm LETTER/S
Gives the
.Dq variable part
(for example, the
.Dq S
or
.Dq D
in
.Dq EST
or
.Dq EDT )
of time zone abbreviations to be used when this rule is in effect.
If this field is
.Dq \- ,
the variable part is null.
.El
.Pp
A zone line has the form:
.Bd -literal -offset 3n
Zone NAME GMTOFF RULES/SAVE FORMAT [UNTILYEAR [MONTH [DAY [TIME]]]]
.Ed
.Pp
For example:
.Bd -literal -offset 3n
Zone Australia/Adelaide 9:30 Aus CST 1971 Oct 31 2:00
.Ed
.Pp
The fields that make up a zone line are:
.Bl -tag -width GMTOFF
.It Cm NAME
The name of the time zone.
This is the name used in creating the time conversion information file for the
zone.
.It Cm GMTOFF
The amount of time to add to UTC to get standard time in this zone.
This field has the same format as the
.Em AT
and
.Em SAVE
fields of rule lines;
begin the field with a minus sign if time must be subtracted from UTC.
.It Cm RULES/SAVE
The name of the rule(s) that apply in the time zone or,
alternately, an amount of time to add to local standard time.
If this field is
.Dq \-
then standard time always applies in the time zone.
.It Cm FORMAT
The format for time zone abbreviations in this time zone.
The pair of characters
.Em %s
is used to show where the
.Dq variable part
of the time zone abbreviation goes.
Alternately, a format can use the pair of characters
.Em %z
to stand for the UTC offset in the form
.No \(+- Ns Em hh ,
.No \(+- Ns Em hhmm ,
or
.No \(+- Ns Em hhmmss ,
using the shortest form that does not lose information, where
.Em hh ,
.Em mm ,
and
.Em ss
are the hours, minutes, and seconds east (+) or west (\(mi) of UTC.
Alternately,
a slash
.Pq \&/
separates standard and daylight abbreviations.
.It Cm UNTILYEAR [MONTH [DAY [TIME]]]
The time at which the UTC offset or the rule(s) change for a location.
It is specified as a year, a month, a day, and a time of day.
If this is specified,
the time zone information is generated from the given UTC offset
and rule change until the time specified.
The month, day, and time of day have the same format as the IN, ON, and AT
fields of a rule; trailing fields can be omitted, and default to the
earliest possible value for the missing fields.
.Pp
The next line must be a
.Dq continuation
line; this has the same form as a zone line except that the
string
.Dq Zone
and the name are omitted, as the continuation line will
place information starting at the time specified as the
.Dq until
information in the previous line in the file used by the previous line.
Continuation lines may contain
.Dq until
information, just as zone lines do, indicating that the next line is a further
continuation.
.El
.Pp
A link line has the form:
.Bd -literal -offset indent
Link	LINK-FROM	LINK-TO
.Ed
.Pp
For example:
.Bd -literal -offset indent
Link	Europe/Istanbul	Asia/Istanbul
.Ed
.Pp
The
.Em LINK-FROM
field should appear as the
.Em NAME
field in some zone line;
the
.Em LINK-TO
field is used as an alternate name for that zone.
.Pp
Except for continuation lines,
lines may appear in any order in the input.
.Pp
Lines in the file that describes leap seconds have the following form:
.Bd -literal -offset indent
Leap	YEAR	MONTH	DAY	HH:MM:SS	CORR	R/S
.Ed
.Pp
For example:
.Bd -literal -offset indent
Leap	1974	Dec	31	23:59:60	+	S
.Ed
.Pp
The
.Em YEAR ,
.Em MONTH ,
.Em DAY ,
and
.Em HH:MM:SS
fields tell when the leap second happened.
The
.Em CORR
field
should be
.Dq +
if a second was added
or
.Dq -
if a second was skipped.
.\" There's no need to document the following, since it's impossible for more
.\" than one leap second to be inserted or deleted at a time.
.\" The C Standard is in error in suggesting the possibility.
.\" See Terry J Quinn, The BIPM and the accurate measure of time,
.\" Proc IEEE 79, 7 (July 1991), 894-905.
.\"	or
.\"	.q ++
.\"	if two seconds were added
.\"	or
.\"	.q --
.\"	if two seconds were skipped.
The
.Em R/S
field should be (an abbreviation of)
.Dq Stationary
if the leap second time given by the other fields should be interpreted as UTC
or (an abbreviation of)
.Dq Rolling
if the leap second time given by the other fields should be interpreted as
local wall clock time.
.Sh EXTENDED EXAMPLE
Here is an extended example of
.Nm
input, intended to illustrate many of its features.
.Bd -literal
# Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
Rule	Swiss	1940	only	-	Nov	2	0:00	1:00	S
Rule	Swiss	1940	only	-	Dec	31	0:00	0	-
Rule	Swiss	1941	1942	-	May	Sun>=1	2:00	1:00	S
Rule	Swiss	1941	1942	-	Oct	Sun>=1	0:00	0

Rule	EU	1977	1980	-	Apr	Sun>=1	1:00u	1:00	S
Rule	EU	1977	only	-	Sep	lastSun	1:00u	0	-
Rule	EU	1978	only	-	Oct	 1	1:00u	0	-
Rule	EU	1979	1995	-	Sep	lastSun	1:00u	0	-
Rule	EU	1981	max	-	Mar	lastSun	1:00u	1:00	S
Rule	EU	1996	max	-	Oct	lastSun	1:00u	0	-

# Zone	NAME	GMTOFF	RULES	FORMAT	UNTIL
Zone	Europe/Zurich	0:34:08	-	LMT	1848 Sep 12
		0:29:44	-	BMT	1894 Jun
		1:00	Swiss	CE%sT	1981
		1:00	EU	CE%sT

Link	Europe/Zurich	Switzerland
.Ed
.Pp
In this example, the zone is named Europe/Zurich
but it has an alias as Switzerland.
Zurich was 34 minutes and 8 seconds west of GMT until 1848-09-12 at 00:00,
when the offset changed to 29 minutes and 44 seconds.
After 1894-06-01 at 00:00 Swiss daylight saving rules
(defined with lines beginning with "Rule Swiss") apply,
and the GMT offset became one hour.
From 1981 to the present,
EU daylight saving rules have applied,
and the UTC offset has remained at one hour.
.Pp
In 1940, daylight saving time applied from
November 2 at 00:00 to December 31 at 00:00.
In 1941 and 1942, daylight saving time applied
from the first Sunday in May at 02:00
to the first Sunday in October at 00:00.
The pre-1981 EU daylight-saving rules have no effect here,
but are included for completeness.
Since 1981,
daylight saving has begun on the last Sunday in March at 01:00 UTC.
Until 1995 it ended the last Sunday in September at 01:00 UTC,
but this changed to the last Sunday in October starting in 1996.
.Pp
For purposes of display,
"LMT" and "BMT" were initially used, respectively.
Since Swiss rules and later EU rules were applied,
the display name for the timezone has been CET for standard time
and CEST for daylight saving time.
.Sh FILES
.Bl -tag -width "/usr/share/zoneinfo" -compact
.It Pa /etc/localtime
link to local time zone
.It Pa /usr/share/zoneinfo
standard directory used for created files
.El
.Sh SEE ALSO
.Xr ctime 3 ,
.Xr tzfile 5 ,
.Xr zdump 8
.Sh CAVEATS
For areas with more than two types of local time,
you may need to use local standard time in the
.Em AT
field of the earliest transition time's rule to ensure that
the earliest transition time recorded in the compiled file is correct.
.Pp
If,
for a particular zone,
a clock advance caused by the start of daylight saving
coincides with and is equal to
a clock retreat caused by a change in UTC offset,
.Nm
produces a single transition to daylight saving at the new UTC offset
(without any change in wall clock time).
To get separate transitions
use multiple zone continuation lines
specifying transition instants using universal time.
.\" This file is in the public domain, so clarified as of
.\" 2009-05-17 by Arthur David Olson.