zic

zic [ option ... ] [ filename ... ]

The zic program reads text from the file(s) named on the command line and creates the time conversion information files specified in this input. If a filename is “-”, standard input is read.

--version

Output version information and exit.

--help

Output short usage message and exit.

-d directory

Create time conversion information files in the named directory rather than in the standard directory named below.

-l timezone

Use timezone as local time. zic will act as if the input contained a link line of the form

Link timezone localtime

-p timezone

Use timezone's rules when handling POSIX-format timezone environment variables. zic will act as if the input contained a link line of the form

Link timezone posixrules

-L 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.

-v

Be more verbose, and complain about the following situations:

-s

Limit time values stored in output files to values that are the same whether they're taken to be signed or unsigned. You can use this option to generate SVVS-compatible files.

Input files should be text files, that is, they should be a series of zero or more lines, each ending in a newline byte and containing at most 511 bytes, and without any NUL bytes. The input text's encoding is typically UTF-8 or ASCII; it should have a unibyte representation for the POSIX Portable Character Set (PPCS) ⟨http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap06.html⟩ and the encoding's non-unibyte characters should consist entirely of non-PPCS bytes. Non-PPCS characters typically occur only in comments: although output file names and time zone abbreviations can contain nearly any character, other software will work better if these are limited to the restricted syntax described under the -v option.

Input lines are made up of fields. Fields are separated from one another by one or more white space characters. The white space characters are space, form feed, carriage return, newline, tab, and vertical tab. Leading and trailing white space 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. Nonblank lines are expected to be of one of three types: rule lines, zone lines, and link lines.

Names must be in English and are case insensitive. They appear in several contexts, and include month and weekday names and keywords such as maximum, only, Rolling, and Zone. A name can be abbreviated by omitting all but an initial prefix; any abbreviation must be unambiguous in context.

A rule line has the form

Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S

For example:

Rule	US	1967	1973	-	Apr	lastSun	2:00w	1:00	D

NAME

Gives the name of the rule set that contains this line. The name must start with a character that is neither an ASCII digit nor “-” nor “+”. To allow for future extensions, an unquoted name should not contain characters from the set “!$%&'()*,/:;<=>?@[\]^`{|}~”.

FROM

Gives the first year in which the rule applies. Any signed integer year can be supplied; the proleptic Gregorian calendar is assumed, with year 0 preceding year 1. The word minimum (or an abbreviation) means the indefinite past. The word maximum (or an abbreviation) means the indefinite future. 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.

TO

Gives the final year in which the rule applies. In addition to minimum and maximum (as above), the word only (or an abbreviation) may be used to repeat the value of the FROM field.

TYPE

should be “-” and is present for compatibility with older versions of zic in which it could contain year types.

IN

Names the month in which the rule takes effect. Month names may be abbreviated.

ON

Gives the day on which the rule takes effect. Recognized forms include:

5	the fifth of the month
lastSun	the last Sunday in the month
lastMon	the last Monday in the month
Sun>=8	first Sunday on or after the eighth
Sun<=25	last Sunday on or before the 25th

A weekday name (e.g., Sunday) or a weekday name preceded by “last” (e.g., lastSunday) may be abbreviated or spelled out in full. Note that there must be no spaces within the ON field.

AT

Gives the time of day at which the rule takes effect. Recognized forms include:

2	time in hours
2:00	time in hours and minutes
01:28:14	time in hours, minutes, and seconds
15:00	24-hour format time (for times after noon)
260:00	260 hours after 00:00
-2:30	2.5 hours before 00:00
-	equivalent to 0

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 w if the given time is local “wall clock” time, s if the given time is local “standard” time, or u (or g or z) if the given time is universal time; in the absence of an indicator, wall clock time is assumed. The intent is that a rule line describes the instants when a clock/calendar set to the type of time specified in the AT field would show the specified date and time of day.

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 AT field (although, of course, the w and s suffixes are not used). Negative offsets are allowed; in Ireland, for example, daylight saving time is observed in winter and has a negative offset relative to Irish Standard Time. The offset is merely added to standard time; for example, zic does not distinguish a 10:30 standard time plus an 0:30 SAVE from a 10:00 standard time plus a 1:00 SAVE.

LETTER/S

Gives the “variable part” (for example, the “S” or “D” in “EST” or “EDT”) of time zone abbreviations to be used when this rule is in effect. If this field is “-”, the variable part is null.

A zone line has the form

Zone	NAME	UTOFF	RULES	FORMAT	[UNTIL]

For example:

Zone	Asia/Amman	2:00	Jordan	EE%sT	2017 Oct 27 01:00

NAME

The name of the timezone. This is the name used in creating the time conversion information file for the timezone. It should not contain a file name component “.” or “..”; a file name component is a maximal substring that does not contain “/”.

UTOFF

The amount of time to add to UT to get standard time. This field has the same format as the AT and SAVE fields of rule lines; begin the field with a minus sign if time must be subtracted from UT.

RULES

The name of the rules that apply in the timezone or, alternatively, a field in the same format as a rule-line SAVE column, giving of the amount of time to be added to local standard time effect, and whether the resulting time is standard or daylight saving. If this field is - then standard time always applies. When an amount of time is given, only the sum of standard time and this amount matters.

FORMAT

The format for time zone abbreviations. The pair of characters %s is used to show where the “variable part” of the time zone abbreviation goes. Alternatively, a format can use the pair of characters %z to stand for the UT offset in the form ±hh, ±hhmm, or ±hhmmss, using the shortest form that does not lose information, where hh, mm, and ss are the hours, minutes, and seconds east (+) or west (−) of UT. Alternatively, a slash (/) separates standard and daylight abbreviations. To conform to POSIX, a time zone abbreviation should contain only alphanumeric ASCII characters, “+” and “-”.

UNTIL

The time at which the UT offset or the rule(s) change for a location. It takes the form of YEAR [MONTH [DAY [TIME]]]. If this is specified, the time zone information is generated from the given UT offset and rule change until the time specified, which is interpreted using the rules in effect just before the transition. 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.

The next line must be a “continuation” line; this has the same form as a zone line except that the string “Zone” and the name are omitted, as the continuation line will place information starting at the time specified as the “until” information in the previous line in the file used by the previous line. Continuation lines may contain “until” information, just as zone lines do, indicating that the next line is a further continuation.

If a zone changes at the same instant that a rule would otherwise take effect in the earlier zone or continuation line, the rule is ignored. In a single zone it is an error if two rules take effect at the same instant, or if two zone changes take effect at the same instant.

A link line has the form

Link	TARGET	LINK-NAME

For example:

Link	Europe/Istanbul	Asia/Istanbul

Except for continuation lines, lines may appear in any order in the input. However, the behavior is unspecified if multiple zone or link lines define the same name, or if the source of one link line is the target of another.

Lines in the file that describes leap seconds have the following form:

Leap	YEAR	MONTH	DAY	HH:MM:SS	CORR	R/S

For example:

Leap	2016	Dec	31	23:59:60	+	S

Here is an extended example of zic input, intended to illustrate many of its features. In this example, the EU rules are for the European Union and for its predecessor organization, the European Communities.

# Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
Rule	Swiss	1941	1942	-	May	Mon>=1	1:00	1:00	S
Rule	Swiss	1941	1942	-	Oct	Mon>=1	2:00	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	UTOFF	RULES	FORMAT	[UNTIL]
Zone	Europe/Zurich	0:34:08	-	LMT	1853 Jul 16
		0:29:46	-	BMT	1894 Jun
		1:00	Swiss	CE%sT	1981
		1:00	EU	CE%sT

Link	Europe/Zurich	Europe/Vaduz

In this example, the timezone is named Europe/Zurich but it has an alias as Europe/Vaduz. This example says that Zurich was 34 minutes and 8 seconds east of UT until 1853-07-16 at 00:00, when the legal offset was changed to 7°26′22.50″; although this works out to 0:29:45.50, the input format cannot represent fractional seconds so it is rounded here. After 1894-06-01 at 00:00 the UT offset became one hour and Swiss daylight saving rules (defined with lines beginning with “Rule Swiss”) apply. From 1981 to the present, EU daylight saving rules have applied, and the UTC offset has remained at one hour.

In 1941 and 1942, daylight saving time applied from the first Monday in May at 01:00 to the first Monday in October at 02:00. 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.

For purposes of display, “LMT” and “BMT” were initially used, respectively. Since Swiss rules and later EU rules were applied, the time zone abbreviation has been CET for standard time and CEST for daylight saving time.

/etc/localtime

Default local timezone file.

/usr/share/zoneinfo

Default timezone information directory.

For areas with more than two types of local time, you may need to use local standard time in the AT field of the earliest transition time's rule to ensure that the earliest transition time recorded in the compiled file is correct.

If, for a particular timezone, a clock advance caused by the start of daylight saving coincides with and is equal to a clock retreat caused by a change in UT offset, zic produces a single transition to daylight saving at the new UT offset (without any change in wall clock time). To get separate transitions use multiple zone continuation lines specifying transition instants using universal time.

tzfile(5), zdump(8)

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