tzset tzsetwall - initialize time conversion information
If TZ does not appear in the environment, the best available approximation to local wall clock time, as specified by the tzfile(5)Ns-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)Ns-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)Ns-format file and cannot be interpreted as a direct specification, UTC is used.
function sets things up so that localtime(3) returns the best available approximation of local wall clock time.
std offset Bo dst Bq Em offset Bq , Em rule Bc
hh Bo : mm Bq Em : ss Bc
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 indicated by an optional preceding (`+' ) ).
where the first date describes when the change from standard to summer time occurs and the second date describes when the change back happens. 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:
The time has the same format as offset 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 the TZ specification, the rules specified by the tzfile(5)Ns-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.
If the file /usr/share/zoneinfo/GMT does not exist, UTC leap seconds are loaded from /usr/share/zoneinfo/posixrules
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Created 1996-2023 by Maxim Chirkov
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