TZ
Defines time zone information. This information is used by date(C) to display the appropriate time. The variable may have any value of the form:

std offset [ dst [ offset ],[ start [ /time ], end [ /time ]]]

(You may also have:

std offset [ dst [ offset ];[ start [ /time ], end [ /time ]]]

which is the XENIX format. Note that this format is not POSIX compatible.)

std, the standard local time zone abbreviation (1-9 characters), and offset, the difference between the local time and GMT, are the only mandatory fields.

offset should be specified as:

[ + | - ] hh [ :mm [ :ss ]]

where hh is hours (0-24), mm is minutes (0-59), and ss is seconds (0-59). Only the hours field is mandatory. If offset is preceded by a minus (-), it is east of the Prime Meridian, otherwise it is assumed to be west (this can be specified with an optional plus (+)).

dst is a 1-9 character abbreviation for the local summertime timezone. If dst is not specified, the system will not be aware of summertime; it will always be on standard time.

The offset after dst is the difference between local standard time and local summertime. If you do not specify an offset, it is assumed to be one hour. (This is usually what you want.)

Everything following the second offset is the rule for when to change from standard to summertime. start/time is when the change to summertime occurs; end/time is when the time changes back. (Note that, for systems in the Southern Hemisphere, start/time does not have to come earlier in the year than end/time.)

start and end describe the day, while time specifies the time. time is specified in the same way as offset (see above), but the leading ``+'' or ``-'' is not valid. If time is not specified, it is assumed to be 02:00:00 (2 A.M.).

start and end can be specified in any of the following ways:


Jn
The Julian day (1-365). Leap years are not counted; February 28 is day 59 and March 1 is day 60, always.

n
The zero-based Julian day (0-365); you can refer to February 29 in a leap year.

Wn.d
The dth day (0-6, where 0 is Sunday) of week n (1-4).

Mm.n.d
The dth day (0-6, where 0 is Sunday) of week n (1-5) of month m (1-12). If you specify the week (n) as 5, this means the last d day in m month, as in M8.5.1 which would be the last Monday in August.

If you specify the comma starting off the summertime rule, it is advisable to specify the rest of the rule.

A sample TZ for Eastern Standard Time, EST, might look like this:

EST5:00:00EDT4:00:00,M4.1.0/2:00:00,M10.5.0/2:00:00.

We start off with ``EST5:00'': this names our time zone and defines it as five hours west of Greenwich Mean Time. Summertime in this locale is called EDT (Eastern Daylight Time), and is four hours ahead of GMT. Summertime starts on a Sunday in the first week in April at 2 A.M., and standard time resumes on the last Sunday in October at 2 A.M.

Refer to the tz(M) and timezone(F) manual pages for more information on TZ.