time zone compiler
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
”, the standard input is
These options are available:
- Create time conversion information files in the named directory rather
than in the standard directory named below.
- Read leap second information from the file with the given name. If this
option is not used, no leap second information appears in output
- Use the given time zone as local time.
zic will act as if the input contained
a link line of the form
Link timezone localtime
- Use the given time zone's rules when handling POSIX-format time zone
zic will act as
if the input contained a link line of the form
Link timezone posixrules
- Complain if a year that appears in a data file is outside the range of
years representable by
Also complain if a time of 24:00 (which cannot be handled by pre-1998
zic) appears in the
- Use the given command rather than
yearistype when checking year types (see
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.
Names (such as month names) must be in English and are case insensitive.
Abbreviations, if used, must be unambiguous in context.
A rule line has the form:
Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S
Rule US 1967 1973 - Apr lastSun 2:00 1:00 D
The fields that make up a rule line are:
- Gives the (arbitrary) name of the set of rules this rule is part of.
- Gives the first year in which the rule applies. Any integer year can be
supplied; the Gregorian calendar is assumed. The word
minimum (or an abbreviation) means the
minimum year representable as an integer. The word
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
- Gives the final year in which the rule applies. In addition to
maximum (as above), the word
only (or an abbreviation) may be used to
repeat the value of the FROM field.
- Gives the type of year in which the rule applies. If
-” then the rule applies
in all years between FROM and
TO inclusive. If
TYPE is something else, then
zic executes the command
to check the type of a year: an exit status of zero is taken to mean that
the year is of the given type; an exit status of one is taken to mean that
the year is not of the given type.
- Names the month in which the rule takes effect. Month names may be
- Gives the day on which the rule takes effect. Recognized forms include:
Names of days of the week may be abbreviated or spelled out in full. Note
that there must be no spaces within the ON
- the fifth of the month
- the last Sunday in the month
- the last Monday in the month
- first Sunday on or after the eighth
- last Sunday on or before the 25th
- Gives the time of day at which the rule takes effect. Recognized forms
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.
- time in hours
- time in hours and minutes
- 24-hour format time (for times after noon)
- time in hours, minutes, and seconds
- equivalent to 0
- 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).
- 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
A zone line has the form:
Zone NAME GMTOFF RULES/SAVE FORMAT [UNTILYEAR [MONTH [DAY [TIME]]]]
Zone Australia/Adelaide 9:30 Aus CST 1971 Oct 31 2:00
The fields that make up a zone line are:
- The name of the time zone. This is the name used in creating the time
conversion information file for the zone.
- The amount of time to add to UTC to get standard time in this zone. 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 UTC.
- 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
“-” then standard time always applies in the time zone.
- The format for time zone abbreviations in this time zone. The pair of
characters %s is used to show where the
“variable part” of the time zone abbreviation goes.
Alternately, a slash (/) separates standard and daylight
[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.
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.
A link line has the form:
Link Europe/Istanbul Asia/Istanbul
field should appear as the
field in some zone line; the
field is used as an alternate name for
Except for continuation lines, lines may appear in any order in the input.
Lines in the file that describes leap seconds have the following form:
Leap YEAR MONTH DAY HH:MM:SS CORR R/S
Leap 1974 Dec 31 23:59:60 + S
, and HH:MM:SS
fields tell when the leap second happened. The
field should be “+” if a
second was added or “-” if a second was skipped. The
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.
Here is an extended example of
intended to illustrate many of its features.
# 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
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.
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.
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.
- link to local time zone
- standard directory used for created files
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 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
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.