zic Command

A rule line has the form:

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

The fields that make up the rule line are as follows:

NAME

Provides a random name for the set of rules for which this Rule is applicable.

FROM

Provides the first year in which the rule applies. Specifying minimum (min) indicates the minimum year with a representable time value. Specifying maximum (max) indicates the maximum year with a representable time value.

TO

Provides the final year in which the rule applies. This is indicated as a valid time value or by specifying minimum and maximum. Specifying only is used to repeat the value of the FROM field.

TYPE

Provides the type of year in which the rule applies.

The TYPE field has the following values:

'-'

The rule applies in all years between FROM and TO, inclusively.

uspres

The rule applies in U.S. Presidential election years.

nonpres

The rule applies in years other than U.S. Presidential election years.

If the TYPE field has a value other than what is mentioned above, the zic command runs the /usr/sbin/yearistype year type command to check the type of year.

The yearistype command accepts two parameters; the year and the type of year. An exit status of 0 is taken to mean that the year is of the given type. Otherwise, 1 is returned as exit status.

IN

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

ON

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

• lastFri represents the last Friday in the month.
• lastMon represents the last Monday in the month.
• A number representing the day of the month. For example, 5 represents the fifth of the month.
• lastSun represents the last Sunday in the month.
• lastMon represents the last Monday in the month.
• Sun>=8 represents first Sunday on or after the eighth.
• Sun<=25 represents last Sunday on or before the 25th.

Names of days of the week can be abbreviated or spelled out in full. Note that there must be no spaces within the ON field.

AT

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

• A number representing time in hours. For example, 2 indicates two hours.
• 2:00 indicates two o'clock in hours and minutes.
• 15:00 represents 3 o'clock in the afternoon using the 24-hour format time format.
• 1:28:14 indicates one o'clock, twenty-eight minutes and fourteen seconds, using the hours, minutes, seconds format.

Any of these forms may be followed by the letter w if the given time is local wall-clock time or s if the given time is local standard time. In the absence of w or s, wall-clock time is assumed.

Regions with more than two types of local time are required to use the local standard time in the AT field of the earliest transition time's rule to ensure the accuracy of the earliest transition time that is stored in the resulting time-zone binary.

SAVE

Prepresents 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 The w and s suffixes are not valid with this field.

LETTER/S

Provides the variable part of the time-zone abbreviations that are used when this rule is in effect. When this field contains - (hyphen), the variable is null. The S character is used to indicate EST and the D character is used to indicate EDT.

A zone line has the form:

Zone   NAME   GMTOFF   RULES/SAVE   FORMAT   [UNTIL]

The fields that make up a zone line are:

NAME

Indicates the name of the time zone. This is the name used to create the time conversion information file for the zone.

GMTOFF

Indicated the amount of time to add to GMT 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 GMT.

RULES/SAVE

Indicated the name of the rules that apply in the time zone or, alternately, an amount of time to add to local standard time. If value of this field is - (hyphen), then standard time always applies in the time zone.

FORMAT

Indicates the format for time zone abbreviations in this time zone. The %s characters are used to show where the variable part of the time zone abbreviation goes.

UNTIL

Indicates the time at which the GMT offset or the rules change for a location. It is specified as year, month, day, and time of day. If this is specified, the time zone information is generated from the given GMT offset and rule change until the time specified.

The next line must be a continuation line. The continuation line places information starting at the time specified in the UNTIL field of the previous line into the file used by the previous line. This line has the same format as a zone line, except that the Zone string and the name are omitted. Continuation lines can contain an UNTIL field, just as zone lines do, indicating that the next line is a further continuation.

A link line has the form:

Link    LINK-FROM    LINK-TO

The LINK-FROM field should appear as the NAME field in a zone line; the LINK-TO field is used as an alternate name for that zone.