All rights reserved.
This code is derived from software contributed to Berkeley by
Arthur Olson.
%sccs.include.redist.man%
@(#)tzset.3 5.1 (Berkeley) 12/04/90
void tzset() void tzsetwall()
If TZ does not appear in the environment, the best available approximation to local wall clock time, as specified by the tzfile (5)-format file ``/etc/localtime'' is used.
If TZ appears in the environment but its value is a null string, Coordinated Universal Time (UTC) is used (without leap second correction).
If TZ appears in the environment and its value begins with a colon (``:''), the rest of its value is used as a pathname of a tzfile (5)-format file from which to read the time conversion information. If the first character of the pathname is a slash (``/'') it is used as an absolute pathname; otherwise, it is used as a pathname relative to the system time conversion information directory.
If its value does not begin with a colon, it is first used as the pathname of a file (as described above) from which to read the time conversion information. If that file cannot be read, the value is then interpreted as a direct specification (the format is described below) of the time conversion information.
If the TZ environment variable does not specify a tzfile (5)-format file and cannot be interpreted as a direct specification, UTC is used.
Tzsetwall sets things up so that localtime returns the best available approximation of local wall clock time.
Where:
15 std " and " dst Three or more bytes that are the designation for the standard ( std ) or summer ( dst ) time zone. Only std is required; if dst is missing, then summer time does not apply in this locale. Upper- and lowercase letters are explicitly allowed. Any characters except a leading colon ( : ), digits, comma ( , ), minus ( - ), plus ( \(pl ), and ASCII NUL are allowed.
offset Indicates the value one must add to the local time to arrive at Coordinated Universal Time. The offset has the form:
hh[:mm[:ss]]
rule Indicates when to change to and back from summer time. The rule has the form:
date/time,date/time
10 J n The Julian day n "(1 \(<=" " n " "\(<= 365). Leap days are not counted; that is, in all years \(em including leap years \(em February 28 is day 59 and March 1 is day 60. It is impossible to explicitly refer to the occasional February 29.
n The zero-based Julian day "(0 \(<=" " n " "\(<= 365). Leap days are counted, and it is possible to refer to February 29.
M m . n . d The d' th day "(0 \(<=" " d " "\(<= 6) of week n of month m of the year "(1 \(<=" " n " "\(<= 5, "1 \(<=" " m " "\(<= 12, where week 5 means ``the last d day in month m '' which may occur in either the fourth or the fifth week). Week 1 is the first week in which the d' th day occurs. Day zero is Sunday.
If no rule is present in the TZ specification, the rules specified by the tzfile (5)-format file posixrules in the system time conversion information directory are used, with the standard and summer time offsets from UTC replaced by those specified by the offset values in TZ .
For compatibility with System V Release 3.1, a semicolon ( ; ) may be used to separate the rule from the rest of the specification.
/usr/share/zoneinfo time zone directory
/usr/share/zoneinfo/posixrules rules for POSIX-style TZ's
/usr/share/zoneinfo/GMT for UTC leap seconds If /usr/share/zoneinfo/GMT is absent, UTC leap seconds are loaded from /usr/share/zoneinfo/posixrules .