Input files use the format described in this section; output
files use tzfile(5) format.
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 1:00d D
The fields that make up a rule line are:
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. There must be no white space characters
within the ON field. The '<=' and '>=' constructs can
result in a day in the neighboring month; for example, the
IN-ON combination 'Oct Sun>=31' stands for the first
Sunday on or after October 31, even if that Sunday occurs
in November.
AT Gives the time of day at which the rule takes effect,
relative to 00:00, the start of a calendar day.
Recognized forms include:
2 time in hours
2:00 time in hours and minutes
01:28:14 time in hours, minutes, and seconds
00:19:32.13 time with fractional seconds
12:00 midday, 12 hours after 00:00
15:00 3 PM, 15 hours after 00:00
24:00 end of day, 24 hours after 00:00
260:00 260 hours after 00:00
-2:30 2.5 hours before 00:00
- equivalent to 0
Although zic rounds times to the nearest integer second
(breaking ties to the even integer), the fractions may be
useful to other applications requiring greater precision.
The source format does not specify any maximum precision.
Any of these forms may be followed by the letter w if the
given time is local or 'wall clock' time, s if the given
time is standard time without any adjustment for daylight
saving, or u (or g or z) if the given time is universal
time; in the absence of an indicator, local (wall clock)
time is assumed. These forms ignore leap seconds; for
example, if a leap second occurs at 00:59:60 local time,
'1:00' stands for 3601 seconds after local midnight
instead of the usual 3600 seconds. 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, and whether the resulting
time is standard or daylight saving. This field has the
same format as the AT field except with a different set of
suffix letters: s for standard time and d for daylight
saving time. The suffix letter is typically omitted, and
defaults to s if the offset is zero and to d otherwise.
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 STDOFF RULES FORMAT [UNTIL]
For example:
Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27 01:00
The fields that make up a zone line are:
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 '/'.
STDOFF The amount of time to add to UT to get standard time,
without any adjustment for daylight saving. 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 one to four fields 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. A zone or continuation line L with a named rule set
starts with standard time by default: that is, any of L's
timestamps preceding L's earliest rule use the rule in effect
after L's first transition into standard time. 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
The TARGET field should appear as the NAME field in some zone
line. The LINK-NAME field is used as an alternative name for
that zone; it has the same syntax as a zone line's NAME field.
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.
The file that describes leap seconds can have leap lines and an
expiration line. Leap lines have the following form:
Leap YEAR MONTH DAY HH:MM:SS CORR R/S
For example:
Leap 2016 Dec 31 23:59:60 + S
The YEAR, MONTH, DAY, and HH:MM:SS fields tell when the leap
second happened. The CORR field should be '+' if a second was
added or '-' if a second was skipped. The R/S field should be
(an abbreviation of) 'Stationary' if the leap second time given
by the other fields should be interpreted as UTC or (an
abbreviation of) 'Rolling' if the leap second time given by the
other fields should be interpreted as local (wall clock) time.
The expiration line, if present, has the form:
Expires YEAR MONTH DAY HH:MM:SS
For example:
Expires 2020 Dec 28 00:00:00
The YEAR, MONTH, DAY, and HH:MM:SS fields give the expiration
timestamp in UTC for the leap second table; zic outputs this
expiration timestamp by truncating the end of the output file to
the timestamp. If there is no expiration line, zic also accepts
a comment '#expires E ...' where E is the expiration timestamp as
a decimal integer count of seconds since the Epoch, not counting
leap seconds. However, the '#expires' comment is an obsolescent
feature, and the leap second file should use an expiration line
instead of relying on a comment.
