| ZIC(8) | System Manager's Manual | ZIC(8) | 
zic —
| zic | [ --version]
      [--help]
      [-b] [-ddirectory] [-Lleapsecondfilename] [-llocaltime] [-pposixrules] [-s]
      [-tfile]
      [-v] [-ycommand] [file ...] | 
zic program reads text from the file(s) named on the
  command line and creates the timezone information format (TZif) files
  specified in this input. If a file is
  ‘-’, standard input is read.
--version--help-b
    bloatfat’, generate additional data
      entries that work around potential bugs or incompatibilities in older
      software, such as software that mishandles the 64-bit generated data. If
      bloat is
      ‘slim’, keep the output files small;
      this can help check for the bugs and incompatibilities. The default is
      ‘slim’, as software that mishandles
      64-bit data typically mishandles timestamps after the year 2038 anyway.
      Also see the -r option for another way to alter
      output size.-d
    directory-l
    timezonezic will act as if the input contained a link line
      of the form
    
    Link
      timezone localtimeIf timezone is
        ‘-’, any already-existing link is
        removed.
-L
    leapsecondfilename-p
    timezoneEET-2EEST’ that lack
      transition rules. zic will act as if the input
      contained a link line of the form
    
    Link
      timezone posixrulesUnless timezone is
        ‘-’, this option is obsolete and
        poorly supported. Among other things it should not be used for
        timestamps after the year 2037, and it should not be combined with
        -b slim if
        timezone's transitions are at standard time or
        Universal Time (UT) instead of local time. If
        timezone is
        ‘-’, any already-existing link is
        removed.
-r
    [@lo[/@hi]]-00’ in place of the omitted
      timestamp data. For example,
    
    zic -r @0omits data intended for negative timestamps (i.e., before the Epoch), and
zic -r
      @0/@2147483648outputs data intended only for nonnegative timestamps that fit into 31-bit signed integers. Or using date(1),
zic -r @$(date +%s)omits data intended for past timestamps. Although this option
        typically reduces the output file's size, the size can increase due to
        the need to represent the timestamp range boundaries, particularly if
        hi causes a TZif file to contain explicit entries
        for pre-hi transitions
        rather than concisely representing them with an extended POSIX TZ
        string. Also see the -b
        slim option for another way to shrink output
        size.
-R
    @hi-t
    file-vzic itself through
          release 2022e.zic prohibit 24:00, and pre-2007 versions
          prohibit times greater than 24:00.zic prohibit this.%z’ format. Pre-2015 versions
          of zic do not support this.zic do not support this.zic due to a longstanding coding
          bug. These abbreviations include
          ‘L’ for
          ‘Link’,
          ‘mi’ for
          ‘min’,
          ‘Sa’ for
          ‘Sat’, and
          ‘Su’ for
          ‘Sun’.zic output formats.
          These compatibility issues affect only timestamps before 1970 or after
          the start of 2038.-L option is used, and either an
          ‘Expires’ line is present or the
          -r option is also used.-’,
          ‘/’, or
          ‘_’; or it contains a file name
          component that contains more than 14 bytes or that starts with
          ‘-’.-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 | - | 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:
-’ nor
      ‘+’. To allow for future extensions,
      an unquoted name should not contain characters from the set
      ‘!$%&'()*,/:;<=>?@[\]^`{|}~’.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.minimum’ and
      ‘maximum’ (as above), the word
      ‘only’ (or an abbreviation) may be
      used to repeat the value of the FROM field.--’ for
      compatibility with older versions of zic. It was
      previously known as the TYPE field, which could
      contain values to allow a separate script to further restrict in which
      “types” of years the rule would apply.Names of days of the week may be abbreviated or spelled out in
        full. 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.
22:0001:28:1400:19:32.1312:0015:0024:00260:00-2:30-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.
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.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/SAVE | FORMAT | [UNTIL] | 
For example:
| Zone | Asia/Amman | 2:00 | Jordan | EE%sT | 2017 Oct 27 1:00 | 
The fields that make up a zone line are:
.’ or
      ‘..’; a file name component is a
      maximal substring that does not contain
      ‘/’.-’ then standard time always
      applies. When an amount of time is given, only the sum of standard time
      and this amount matters.%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
      ‘-’. By convention, the time zone
      abbreviation ‘-00’ is a placeholder
      that means local time is unspecified.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.
If a continuation line subtracts N seconds from the UT offset after a transition that would be interpreted to be later if using the continuation line's UT offset and rules, the UNTIL time of the previous zone or continuation line is interpreted according to the continuation line's UT offset and rules, and any rule that would otherwise take effect in the next N seconds is instead assumed to take effect simultaneously. For example:
| # Rule | NAME | FROM | TO | - | IN | ON | AT | SAVE | LETTER/S | 
| Rule | US | 1967 | 2006 | - | Oct | lastSun | 2:00 | 0 | S | 
| Rule | US | 1967 | 1973 | - | Apr | lastSun | 2:00 | 1:00 | D | 
| # Zone | NAME | STDOFF | RULES | FORMAT | [UNTIL] | 
| Zone | America/Menominee | -5:00 | - | EST | 1973 Apr 29 2:00 | 
| -6:00 | US | C%sT | 
Here, an incorrect reading would be there were two clock changes
    on 1973-04-29, the first from 02:00 EST (-05) to 01:00 CST (-06), and the
    second an hour later from 02:00 CST (-06) to 03:00 CDT (-05). However,
    zic interprets this more sensibly as a single
    transition from 02:00 CST (-05) to 02:00 CDT (-05).
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 or as the LINK-NAME field in some link 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. Links can chain together, although the behavior is unspecified if a chain of one or more links does not terminate in a Zone name. A link line can appear before the line that defines the link target. For example:
| Link | Greenwich | G_M_T | 
| Link | Etc/GMT | Greenwich | 
| Zone | Etc/GMT 0 | - GMT | 
The two links are chained together, and G_M_T, Greenwich, and Etc/GMT all name the same zone.
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.
| 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.
Rolling leap seconds were implemented back when it was not clear
    whether common practice was rolling or stationary, with concerns that one
    would see Times Square ball drops where there'd be a “3... 2... 1...
    leap... Happy New Year” countdown, placing the leap second at
    midnight New York time rather than midnight UTC. However, this countdown
    style does not seem to have caught on, which means rolling leap seconds are
    not used in practice; also, they are not supported if the
    -r option is used.
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 input, intended to
  illustrate many of its features.
| # Rule | NAME | FROM | TO | - | 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 | STDOFF | RULES/SAVE | FORMAT | [UNTIL] | 
| Zone | Europe/Zurich | 0:34:08 | - | LMT | 1853 Jul 16 | 
| 0:29:45.50 | - | BMT | 1894 Jun | ||
| 1:00 | Swiss | CE%sT | 1981 | ||
| 1:00 | EU | CE%sT | 
| Link | Europe/Zurich | Europe/Vaduz | 
In this example, the EU rules are for the European Union and for
    its predecessor organization, the European Communities. The timezone is
    named Europe/Zurich and it has the alias 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″; which this works out to 0:29:45.50;
    zic treats this by rounding it to 0:29:46. 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.
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
    local (wall clock) time. To get separate transitions use multiple zone
    continuation lines specifying transition instants using universal time.
| December 6, 2023 | NetBSD 10.1 |