Command format


TZ= standardHH[:MM[:SS]] [daylight[HH[:MM[:SS:]]] [,startdate[/starttime],enddate[/endtime]] ]


All commands assume that times stored in the file system and returned by the operating system are stored using Universal Time Coordinated (UTC), hereafter referred to as the universal reference time. The mapping from the universal reference time to local time is specified by the TZ (time zone) environment variable.

The value of the TZ environment variable has these fields (two required and three optional):
An alphabetic abbreviation for the local standard time zone; for example, GMT, EST, MSEZ.
The time offset westward from the universal reference time. A leading minus sign (-) means that the local time zone is east of the universal reference time. An offset of this form must follow standard and can also optionally follow daylight. An optional colon (:) separates hours from optional minutes and seconds.

If daylight is specified without a daylight offset, daylight saving time is assumed to be one hour ahead of the standard time.

The abbreviation for your local daylight saving time zone. If the daylight field is missing, the conversion to daylight saving time is disabled. The number of hours, minutes, and seconds your local daylight saving time is offset from UTC when daylight saving time is in effect. If the daylight saving time abbreviation is specified, and the offset omitted, the offset of one hour is assumed.
A rule that identifies the start and end of daylight saving time, specifying when it should be in effect. Both the startdate and enddate must be present, and must either take the form Jn, n, or Mm.w.d..
  • Jn is the Julian day n (1 <= n <=365). Leap days are not counted. In all years, including leap years, February 28 is day 59 and March 9 is day 60. It is impossible to implicitly refer to the occasional February 29.
  • n is the zero-based Julian day (0 <= n <= 365). Leap days are counted, and it is possible to refer to February 29.
    Non-leap year
    January 1
    Day 0
    February 28
    Day 58
    March 1
    Day 59
    December 31
    Day 364
    Leap year
    January 1
    Day 0
    February 29
    Day 59
    March 1
    Day 60
    December 31
    Day 365
  • Mm.w.d defines the day (0 <= d <= 6) of week w (1 <= w <= 5) of month m (1 <= 12) of the year. Week 5 has the last day (d) in month m, which may occur in either the fourth or fifth week). Week 1 is the first week in which the dth day occurs. Day zero is Sunday.

Neither starttime nor endtime are required. If they are omitted, their values default to 02:00:00. If this daylight saving time rule is omitted altogether, the values in the rule default to the standard rules for American daylight saving time.

When the TZ variable is not set, time conversions behave as if TZ were set to TZ=GMT0.


This interpretation of the TZ environment variable is a superset of that supported by UNIX System V.


The locale, date and touch commands.