tzset(3)
- NetBSD Manual Pages
TZSET(3) TZSET(3)
NAME
tzset - initialize time conversion information
SYNOPSIS
void tzset(void)
DESCRIPTION
Tzset uses the value of the environment variable TZ to set
time conversion information used by localtime. If TZ does
not appear in the environment, the best available approxi-
mation to local wall clock time, as specified by the
tzfile(5)-format file localtime in the system time conver-
sion information directory, is used by localtime. 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 is not a null string:
if the value begins with a colon, it is used as a
pathname of a file from which to read the time con-
version information;
if the value does not begin with a colon, it is
first used as the pathname of a file from which to
read the time conversion information, and, if that
file cannot be read, is used directly as a specifi-
cation of the time conversion information.
When TZ is used as a pathname, if it begins with a slash,
it is used as an absolute pathname; otherwise, it is used
as a pathname relative to a system time conversion infor-
mation directory. The file must be in the format speci-
fied in tzfile(5).
When TZ is used directly as a specification of the time
conversion information, it must have the following syntax
(spaces inserted for clarity):
stdoffset[dst[offset][,rule]]
Where:
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 let-
ters are explicitly allowed. Any
characters except a leading colon
(:), digits, comma (,), minus (-),
plus (+), and ASCII NUL are allowed.
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TZSET(3) TZSET(3)
offset Indicates the value one must add to
the local time to arrive at Coordi-
nated Universal Time. The offset
has the form:
hh[:mm[:ss]]
The minutes (mm) and seconds (ss)
are optional. The hour (hh) is
required and may be a single digit.
The offset following std is
required. If no offset follows dst,
summer time is assumed to be one
hour ahead of standard time. One or
more digits may be used; the value
is always interpreted as a decimal
number. The hour must be between
zero and 24, and the minutes (and
seconds) -- if present -- between
zero and 59. If preceded by a
``-'', the time zone shall be east
of the Prime Meridian; otherwise it
shall be west (which may be indi-
cated by an optional preceding
``+'').
rule Indicates when to change to and back
from summer time. The rule has the
form:
date/time,date/time
where the first date describes when
the change from standard to summer
time occurs and the second date
describes when the change back hap-
pens. Each time field describes
when, in current local time, the
change to the other time is made.
The format of date is one of the
following:
Jn The Julian day n
(1 <= n <= 365). Leap
days are not counted; that
is, in all years --
including leap years --
February 28 is day 59 and
March 1 is day 60. It is
impossible to explicitly
refer to the occasional
February 29.
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TZSET(3) TZSET(3)
n The zero-based Julian day
(0 <= n <= 365). Leap
days are counted, and it
is possible to refer to
February 29.
Mm.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.
The time has the same format as off-
set except that no leading sign
(``-'' or ``+'') is allowed. The
default, if time is not given, is
02:00:00.
If no rule is present in TZ, the rules specified by the
tzfile(5)-format file posixrules in the system time con-
version information directory are used, with the standard
and summer time offsets from UTC replaced by those speci-
fied 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.
If the TZ environment variable does not specify a
tzfile(5)-format and cannot be interpreted as a direct
specification, UTC is used.
FILES
/etc/localtime local time zone file
/usr/share/zoneinfo time zone information
directory
/usr/share/zoneinfo/posixrules used with 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.
SEE ALSO
getenv(3), ctime(3), strftime(3), time(3), tzfile(5)
STANDARDS
The tzset() function conforms to IEEE Std1003.1-1988
(``POSIX'').
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