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commands/zoneinfo/newctime.3
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.TH NEWCTIME 3
.SH NAME
asctime, ctime, difftime, gmtime, localtime, mktime \- convert date and time to ASCII
.SH SYNOPSIS
.nf
.B extern char *tzname[2];
.PP
.B void tzset()
.PP
.B #include <sys/types.h>
.PP
.B char *ctime(clock)
.B const time_t *clock;
.PP
.B double difftime(time1, time0)
.B time_t time1;
.B time_t time0;
.PP
.B #include <time.h>
.PP
.B char *asctime(tm)
.B const struct tm *tm;
.PP
.B struct tm *localtime(clock)
.B const time_t *clock;
.PP
.B struct tm *gmtime(clock)
.B const time_t *clock;
.PP
.B time_t mktime(tm)
.B struct tm *tm;
.PP
.B cc ... -ltz
.fi
.SH DESCRIPTION
.I Ctime\^
converts a long integer, pointed to by
.IR clock ,
representing the time in seconds since
00:00:00 UTC, 1970-01-01,
and returns a pointer to a
string of the form
.br
.ce
.eo
Thu Nov 24 18:22:48 1986\n\0
.br
.ec
Years requiring fewer than four characters are padded with leading zeroes.
For years longer than four characters, the string is of the form
.br
.ce
.eo
Thu Nov 24 18:22:48 81986\n\0
.ec
.br
with five spaces before the year.
These unusual formats are designed to make it less likely that older
software that expects exactly 26 bytes of output will mistakenly output
misleading values for out-of-range years.
.PP
.I Localtime\^
and
.I gmtime\^
return pointers to ``tm'' structures, described below.
.I Localtime\^
corrects for the time zone and any time zone adjustments
(such as Daylight Saving Time in the United States).
After filling in the ``tm'' structure,
.I localtime
sets the
.BR tm_isdst 'th
element of
.B tzname
to a pointer to an
ASCII string that's the time zone abbreviation to be used with
.IR localtime 's
return value.
.PP
.I Gmtime\^
converts to Coordinated Universal Time.
.PP
.I Asctime\^
converts a time value contained in a
``tm'' structure to a string,
as shown in the above example,
and returns a pointer to the string.
.PP
.I Mktime\^
converts the broken-down time,
expressed as local time,
in the structure pointed to by
.I tm
into a calendar time value with the same encoding as that of the values
returned by the
.I time
function.
The original values of the
.B tm_wday
and
.B tm_yday
components of the structure are ignored,
and the original values of the other components are not restricted
to their normal ranges.
(A positive or zero value for
.B tm_isdst
causes
.I mktime
to presume initially that summer time (for example, Daylight Saving Time
in the U.S.A.)
respectively,
is or is not in effect for the specified time.
A negative value for
.B tm_isdst
causes the
.I mktime
function to attempt to divine whether summer time is in effect
for the specified time.)
On successful completion, the values of the
.B tm_wday
and
.B tm_yday
components of the structure are set appropriately,
and the other components are set to represent the specified calendar time,
but with their values forced to their normal ranges; the final value of
.B tm_mday
is not set until
.B tm_mon
and
.B tm_year
are determined.
.I Mktime\^
returns the specified calendar time;
If the calendar time cannot be represented,
it returns
.BR -1 .
.PP
.I Difftime\^
returns the difference between two calendar times,
.RI ( time1
-
.IR time0 ),
expressed in seconds.
.PP
Declarations of all the functions and externals, and the ``tm'' structure,
are in the
.B <time.h>\^
header file.
The structure (of type)
.B struct tm
includes the following fields:
.RS
.PP
.nf
.ta .5i +\w'long tm_gmtoff;\0\0'u
int tm_sec; /\(** seconds (0 - 60) \(**/
int tm_min; /\(** minutes (0 - 59) \(**/
int tm_hour; /\(** hours (0 - 23) \(**/
int tm_mday; /\(** day of month (1 - 31) \(**/
int tm_mon; /\(** month of year (0 - 11) \(**/
int tm_year; /\(** year \- 1900 \(**/
int tm_wday; /\(** day of week (Sunday = 0) \(**/
int tm_yday; /\(** day of year (0 - 365) \(**/
int tm_isdst; /\(** is summer time in effect? \(**/
char \(**tm_zone; /\(** abbreviation of timezone name \(**/
long tm_gmtoff; /\(** offset from UTC in seconds \(**/
.fi
.RE
.PP
The
.I tm_zone
and
.I tm_gmtoff
fields exist, and are filled in, only if arrangements to do
so were made when the library containing these functions was
created.
There is no guarantee that these fields will continue to exist
in this form in future releases of this code.
.PP
.I Tm_isdst\^
is non-zero if summer time is in effect.
.PP
.I Tm_gmtoff
is the offset (in seconds) of the time represented
from UTC, with positive values indicating east
of the Prime Meridian.
.SH FILES
.ta \w'/usr/share/zoneinfo/posixrules\0\0'u
/usr/share/zoneinfo time zone information directory
.br
/usr/share/zoneinfo/localtime local time zone file
.br
/usr/share/zoneinfo/posixrules used with POSIX-style TZ's
.br
/usr/share/zoneinfo/GMT for UTC leap seconds
.sp
If
.B /usr/share/zoneinfo/GMT
is absent,
UTC leap seconds are loaded from
.BR /usr/share/zoneinfo/posixrules .
.SH SEE ALSO
getenv(3),
newstrftime(3),
newtzset(3),
time(2),
tzfile(5)
.SH NOTES
The return values point to static data;
the data is overwritten by each call.
The
.B tm_zone
field of a returned
.B "struct tm"
points to a static array of characters, which
will also be overwritten at the next call
(and by calls to
.IR tzset ).
.PP
.I Asctime\^
and
.I ctime\^
behave strangely for years before 1000 or after 9999.
The 1989 and 1999 editions of the C Standard say
that years from \-99 through 999 are converted without
extra spaces, but this conflicts with longstanding
tradition and with this implementation.
Traditional implementations of these two functions are
restricted to years in the range 1900 through 2099.
To avoid this portability mess, new programs should use
.I strftime\^
instead.
.PP
Avoid using out-of-range values with
.I mktime
when setting up lunch with promptness sticklers in Riyadh.
.\" @(#)newctime.3 7.17

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commands/zoneinfo/newstrftime.3
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.\" Based on the UCB file whose copyright information appears below.
.\" Copyright (c) 1989, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" from: @(#)strftime.3 5.12 (Berkeley) 6/29/91
.\" $Id: strftime.3,v 1.4 1993/12/15 20:33:00 jtc Exp $
.\"
.TH NEWSTRFTIME 3
.SH NAME
strftime \- format date and time
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <time.h>
.PP
.B size_t strftime(buf, maxsize, format, timeptr)
.B char *buf;
.B size_t maxsize;
.B const char *format;
.B const struct tm *timeptr
.PP
.B cc ... -ltz
.fi
.SH DESCRIPTION
The
.I strftime\^
function formats the information from
.I timeptr\^
into the buffer
.I buf\^
according to the string pointed to by
.IR format\^ .
.PP
The
.I format\^
string consists of zero or more conversion specifications and
ordinary characters.
All ordinary characters are copied directly into the buffer.
A conversion specification consists of a percent sign
.Ql %
and one other character.
.PP
No more than
.I maxsize\^
characters are be placed into the array.
If the total number of resulting characters, including the terminating
null character, is not more than
.IR maxsize\^ ,
.I strftime\^
returns the number of characters in the array, not counting the
terminating null.
Otherwise, zero is returned.
.PP
Each conversion specification is replaced by the characters as
follows which are then copied into the buffer.
.TP
%A
is replaced by the locale's full weekday name.
.TP
%a
is replaced by the locale's abbreviated weekday name.
.TP
%B
is replaced by the locale's full month name.
.TP
%b or %h
is replaced by the locale's abbreviated month name.
.TP
%C
is replaced by the century (a year divided by 100 and truncated to an integer)
as a decimal number (00-99).
.TP
%c
is replaced by the locale's appropriate date and time representation.
.TP
%D
is replaced by the date in the format %m/%d/%y.
.TP
%d
is replaced by the day of the month as a decimal number (01-31).
.TP
%e
is replaced by the day of month as a decimal number (1-31);
single digits are preceded by a blank.
.TP
%F
is replaced by the date in the format %Y-%m-%d.
.TP
%G
is replaced by the ISO 8601 year with century as a decimal number.
.TP
%g
is replaced by the ISO 8601 year without century as a decimal number (00-99).
.TP
%H
is replaced by the hour (24-hour clock) as a decimal number (00-23).
.TP
%I
is replaced by the hour (12-hour clock) as a decimal number (01-12).
.TP
%j
is replaced by the day of the year as a decimal number (001-366).
.TP
%k
is replaced by the hour (24-hour clock) as a decimal number (0-23);
single digits are preceded by a blank.
.TP
%l
is replaced by the hour (12-hour clock) as a decimal number (1-12);
single digits are preceded by a blank.
.TP
%M
is replaced by the minute as a decimal number (00-59).
.TP
%m
is replaced by the month as a decimal number (01-12).
.TP
%n
is replaced by a newline.
.TP
%p
is replaced by the locale's equivalent of either AM or PM.
.TP
%R
is replaced by the time in the format %H:%M.
.TP
%r
is replaced by the locale's representation of 12-hour clock time
using AM/PM notation.
.TP
%S
is replaced by the second as a decimal number (00-60).
.TP
%s
is replaced by the number of seconds since the Epoch, UTC (see mktime(3)).
.TP
%T
is replaced by the time in the format %H:%M:%S.
.TP
%t
is replaced by a tab.
.TP
%U
is replaced by the week number of the year (Sunday as the first day of
the week) as a decimal number (00-53).
.TP
%u
is replaced by the weekday (Monday as the first day of the week)
as a decimal number (1-7).
.TP
%V
is replaced by the week number of the year (Monday as the first day of
the week) as a decimal number (01-53). If the week containing January
1 has four or more days in the new year, then it is week 1; otherwise
it is week 53 of the previous year, and the next week is week 1.
.TP
%W
is replaced by the week number of the year (Monday as the first day of
the week) as a decimal number (00-53).
.TP
%w
is replaced by the weekday (Sunday as the first day of the week)
as a decimal number (0-6).
.TP
%X
is replaced by the locale's appropriate time representation.
.TP
%x
is replaced by the locale's appropriate date representation.
.TP
%Y
is replaced by the year with century as a decimal number.
.TP
%y
is replaced by the year without century as a decimal number (00-99).
.TP
%Z
is replaced by the time zone name,
or by the empty string if this is not determinable.
.TP
%z
is replaced by the offset from UTC in the format +HHMM or -HHMM as appropriate,
with positive values representing locations east of Greenwich,
or by the empty string if this is not determinable.
.TP
%%
is replaced by a single %.
.TP
%+
is replaced by the date and time in date(1) format.
.SH SEE ALSO
date(1),
getenv(3),
newctime(3),
newtzset(3),
time(2),
tzfile(5)
.\" @(#)newstrftime.3 7.15

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commands/zoneinfo/newtzset.3
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.TH NEWTZSET 3
.SH NAME
tzset \- initialize time conversion information
.SH SYNOPSIS
.nf
.B void tzset()
.PP
.B cc ... -ltz
.fi
.SH DESCRIPTION
.I Tzset
uses the value of the environment variable
.B TZ
to set time conversion information used by
.IR localtime .
If
.B TZ
does not appear in the environment,
the best available approximation to local wall clock time, as specified
by the
.IR tzfile (5)-format
file
.B localtime
in the system time conversion information directory, is used by
.IR localtime .
If
.B TZ
appears in the environment but its value is a null string,
Coordinated Universal Time (UTC) is used (without leap second
correction). If
.B TZ
appears in the environment and its value is not a null string:
.IP
if the value begins with a colon, it is used as a pathname of a file
from which to read the time conversion information;
.IP
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 specification of
the time conversion information.
.PP
When
.B 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 information
directory.
The file must be in the format specified in
.IR tzfile (5).
.PP
When
.B TZ
is used directly as a specification of the time conversion information,
it must have the following syntax (spaces inserted for clarity):
.IP
\fIstd\|offset\fR[\fIdst\fR[\fIoffset\fR][\fB,\fIrule\fR]]
.PP
Where:
.RS
.TP 15
.IR std " and " dst
Three or more bytes that are the designation for the standard
.RI ( std )
or summer
.RI ( dst )
time zone. Only
.I std
is required; if
.I 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
.RB ( : ),
digits, comma
.RB ( , ),
minus
.RB ( \(mi ),
plus
.RB ( \(pl ),
and ASCII NUL are allowed.
.TP
.I offset
Indicates the value one must add to the local time to arrive at
Coordinated Universal Time. The
.I offset
has the form:
.RS
.IP
\fIhh\fR[\fB:\fImm\fR[\fB:\fIss\fR]]
.RE
.IP
The minutes
.RI ( mm )
and seconds
.RI ( ss )
are optional. The hour
.RI ( hh )
is required and may be a single digit. The
.I offset
following
.I std
is required. If no
.I offset
follows
.IR 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) \(em if present \(em between zero and 59. If preceded by a
.RB `` \(mi '',
the time zone shall be east of the Prime Meridian; otherwise it shall be
west (which may be indicated by an optional preceding
.RB `` \(pl '').
.TP
.I rule
Indicates when to change to and back from summer time. The
.I rule
has the form:
.RS
.IP
\fIdate\fB/\fItime\fB,\fIdate\fB/\fItime\fR
.RE
.IP
where the first
.I date
describes when the change from standard to summer time occurs and the
second
.I date
describes when the change back happens. Each
.I time
field describes when, in current local time, the change to the other
time is made.
.IP
The format of
.I date
is one of the following:
.RS
.TP 10
.BI J n
The Julian day
.I n
.RI "(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.
.TP
.I n
The zero-based Julian day
.RI "(0\ \(<=" "\ n\ " "\(<=\ 365).
Leap days are counted, and it is possible to refer to February 29.
.TP
.BI M m . n . d
The
.IR d' th
day
.RI "(0\ \(<=" "\ d\ " "\(<=\ 6)
of week
.I n
of month
.I m
of the year
.RI "(1\ \(<=" "\ n\ " "\(<=\ 5,
.RI "1\ \(<=" "\ m\ " "\(<=\ 12,
where week 5 means ``the last
.I d
day in month
.IR m ''
which may occur in either the fourth or the fifth week). Week 1 is the
first week in which the
.IR d' th
day occurs. Day zero is Sunday.
.RE
.IP "" 15
The
.I time
has the same format as
.I offset
except that no leading sign
.RB (`` \(mi ''
or
.RB `` \(pl '')
is allowed. The default, if
.I time
is not given, is
.BR 02:00:00 .
.RE
.LP
If no
.I rule
is present in
.BR TZ ,
the rules specified
by the
.IR tzfile (5)-format
file
.B 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
.I offset
values in
.BR TZ .
.PP
For compatibility with System V Release 3.1, a semicolon
.RB ( ; )
may be used to separate the
.I rule
from the rest of the specification.
.PP
If the
.B TZ
environment variable does not specify a
.IR tzfile (5)-format
and cannot be interpreted as a direct specification,
UTC is used.
.SH FILES
.ta \w'/usr/share/zoneinfo/posixrules\0\0'u
/usr/share/zoneinfo time zone information directory
.br
/usr/share/zoneinfo/localtime local time zone file
.br
/usr/share/zoneinfo/posixrules used with POSIX-style TZ's
.br
/usr/share/zoneinfo/GMT for UTC leap seconds
.sp
If
.B /usr/share/zoneinfo/GMT
is absent,
UTC leap seconds are loaded from
.BR /usr/share/zoneinfo/posixrules .
.SH SEE ALSO
getenv(3),
newctime(3),
newstrftime(3),
time(2),
tzfile(5)
.\" @(#)newtzset.3 7.5

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.TH TIME2POSIX 3
.SH NAME
time2posix, posix2time \- convert seconds since the Epoch
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <time.h>
.PP
.B time_t time2posix(t)
.B time_t t
.PP
.B time_t posix2time(t)
.B time_t t
.PP
.B cc ... -ltz
.fi
.SH DESCRIPTION
IEEE Standard 1003.1
(POSIX)
legislates that a time_t value of
536457599 shall correspond to "Wed Dec 31 23:59:59 UTC 1986."
This effectively implies that POSIX time_t's cannot include leap
seconds and,
therefore,
that the system time must be adjusted as each leap occurs.
.PP
If the time package is configured with leap-second support
enabled,
however,
no such adjustment is needed and
time_t values continue to increase over leap events
(as a true `seconds since...' value).
This means that these values will differ from those required by POSIX
by the net number of leap seconds inserted since the Epoch.
.PP
Typically this is not a problem as the type time_t is intended
to be
(mostly)
opaque\(emtime_t values should only be obtained-from and
passed-to functions such as
.IR time(2) ,
.IR localtime(3) ,
.IR mktime(3) ,
and
.IR difftime(3) .
However,
POSIX gives an arithmetic
expression for directly computing a time_t value from a given date/time,
and the same relationship is assumed by some
(usually older)
applications.
Any programs creating/dissecting time_t's
using such a relationship will typically not handle intervals
over leap seconds correctly.
.PP
The
.I time2posix
and
.I posix2time
functions are provided to address this time_t mismatch by converting
between local time_t values and their POSIX equivalents.
This is done by accounting for the number of time-base changes that
would have taken place on a POSIX system as leap seconds were inserted
or deleted.
These converted values can then be used in lieu of correcting the older
applications,
or when communicating with POSIX-compliant systems.
.PP
.I Time2posix
is single-valued.
That is,
every local time_t
corresponds to a single POSIX time_t.
.I Posix2time
is less well-behaved:
for a positive leap second hit the result is not unique,
and for a negative leap second hit the corresponding
POSIX time_t doesn't exist so an adjacent value is returned.
Both of these are good indicators of the inferiority of the
POSIX representation.
.PP
The following table summarizes the relationship between a time
T and it's conversion to,
and back from,
the POSIX representation over the leap second inserted at the end of June,
1993.
.nf
.ta \w'93/06/30 'u +\w'23:59:59 'u +\w'A+0 'u +\w'X=time2posix(T) 'u
DATE TIME T X=time2posix(T) posix2time(X)
93/06/30 23:59:59 A+0 B+0 A+0
93/06/30 23:59:60 A+1 B+1 A+1 or A+2
93/07/01 00:00:00 A+2 B+1 A+1 or A+2
93/07/01 00:00:01 A+3 B+2 A+3
A leap second deletion would look like...
DATE TIME T X=time2posix(T) posix2time(X)
??/06/30 23:59:58 A+0 B+0 A+0
??/07/01 00:00:00 A+1 B+2 A+1
??/07/01 00:00:01 A+2 B+3 A+2
.sp
.ce
[Note: posix2time(B+1) => A+0 or A+1]
.fi
.PP
If leap-second support is not enabled,
local time_t's and
POSIX time_t's are equivalent,
and both
.I time2posix
and
.I posix2time
degenerate to the identity function.
.SH SEE ALSO
difftime(3),
localtime(3),
mktime(3),
time(2)
.\" @(#)time2posix.3 7.8
.\" This file is in the public domain, so clarified as of
.\" 1996-06-05 by Arthur David Olson.

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.TH TZFILE 5
.SH NAME
tzfile \- time zone information
.SH SYNOPSIS
.B
#include <tzfile.h>
.SH DESCRIPTION
The time zone information files used by
.IR tzset (3)
begin with the magic characters "TZif" to identify then as
time zone information files,
followed by sixteen bytes reserved for future use,
followed by six four-byte values of type
.BR long ,
written in a ``standard'' byte order
(the high-order byte of the value is written first).
These values are,
in order:
.TP
.I tzh_ttisgmtcnt
The number of UTC/local indicators stored in the file.
.TP
.I tzh_ttisstdcnt
The number of standard/wall indicators stored in the file.
.TP
.I tzh_leapcnt
The number of leap seconds for which data is stored in the file.
.TP
.I tzh_timecnt
The number of "transition times" for which data is stored
in the file.
.TP
.I tzh_typecnt
The number of "local time types" for which data is stored
in the file (must not be zero).
.TP
.I tzh_charcnt
The number of characters of "time zone abbreviation strings"
stored in the file.
.PP
The above header is followed by
.I tzh_timecnt
four-byte values of type
.BR long ,
sorted in ascending order.
These values are written in ``standard'' byte order.
Each is used as a transition time (as returned by
.IR time (2))
at which the rules for computing local time change.
Next come
.I tzh_timecnt
one-byte values of type
.BR "unsigned char" ;
each one tells which of the different types of ``local time'' types
described in the file is associated with the same-indexed transition time.
These values serve as indices into an array of
.I ttinfo
structures that appears next in the file;
these structures are defined as follows:
.in +.5i
.sp
.nf
.ta .5i +\w'unsigned int\0\0'u
struct ttinfo {
long tt_gmtoff;
int tt_isdst;
unsigned int tt_abbrind;
};
.in -.5i
.fi
.sp
Each structure is written as a four-byte value for
.I tt_gmtoff
of type
.BR long ,
in a standard byte order, followed by a one-byte value for
.I tt_isdst
and a one-byte value for
.IR tt_abbrind .
In each structure,
.I tt_gmtoff
gives the number of seconds to be added to UTC,
.I tt_isdst
tells whether
.I tm_isdst
should be set by
.I localtime (3)
and
.I tt_abbrind
serves as an index into the array of time zone abbreviation characters
that follow the
.I ttinfo
structure(s) in the file.
.PP
Then there are
.I tzh_leapcnt
pairs of four-byte values, written in standard byte order;
the first value of each pair gives the time
(as returned by
.IR time(2))
at which a leap second occurs;
the second gives the
.I total
number of leap seconds to be applied after the given time.
The pairs of values are sorted in ascending order by time.
.PP
Then there are
.I tzh_ttisstdcnt
standard/wall indicators, each stored as a one-byte value;
they tell whether the transition times associated with local time types
were specified as standard time or wall clock time,
and are used when a time zone file is used in handling POSIX-style
time zone environment variables.
.PP
Finally there are
.I tzh_ttisgmtcnt
UTC/local indicators, each stored as a one-byte value;
they tell whether the transition times associated with local time types
were specified as UTC or local time,
and are used when a time zone file is used in handling POSIX-style
time zone environment variables.
.PP
.I Localtime
uses the first standard-time
.I ttinfo
structure in the file
(or simply the first
.I ttinfo
structure in the absence of a standard-time structure)
if either
.I tzh_timecnt
is zero or the time argument is less than the first transition time recorded
in the file.
.SH SEE ALSO
newctime(3)
.\" @(#)tzfile.5 7.12
.\" This file is in the public domain, so clarified as of
.\" 1996-06-05 by Arthur David Olson.

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.TH TZSELECT 8
.SH NAME
tzselect \- select a time zone
.SH SYNOPSIS
.B tzselect
.SH DESCRIPTION
The
.B tzselect
program asks the user for information about the current location,
and outputs the resulting time zone description to standard output.
The output is suitable as a value for the TZ environment variable.
.PP
All interaction with the user is done via standard input and standard error.
.SH "ENVIRONMENT VARIABLES"
.TP
\f3AWK\fP
Name of a Posix-compliant
.I awk
program (default:
.BR awk ).
.TP
\f3TZDIR\fP
Name of the directory containing time zone data files (default:
.BR /usr/share/zoneinfo ).
.SH FILES
.TP
\f2TZDIR\fP\f3/iso3166.tab\fP
Table of ISO 3166 2-letter country codes and country names.
.TP
\f2TZDIR\fP\f3/zone.tab\fP
Table of country codes, latitude and longitude, TZ values, and
descriptive comments.
.TP
\f2TZDIR\fP\f3/\fP\f2TZ\fP
Time zone data file for time zone \f2TZ\fP.
.SH "EXIT STATUS"
The exit status is zero if a time zone was successfully obtained from the user,
nonzero otherwise.
.SH "SEE ALSO"
newctime(3), tzfile(5), zdump(8), zic(8)
.\" @(#)tzselect.8 1.3

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.TH ZDUMP 8
.SH NAME
zdump \- time zone dumper
.SH SYNOPSIS
.B zdump
[
.B \-\-version
]
[
.B \-v
] [
.B \-c
[loyear,]hiyear ] [ zonename ... ]
.SH DESCRIPTION
.I Zdump
prints the current time in each
.I zonename
named on the command line.
.PP
These options are available:
.TP
.BI "\-\-version"
Output version information and exit.
.TP
.B \-v
For each
.I zonename
on the command line,
print the time at the lowest possible time value,
the time one day after the lowest possible time value,
the times both one second before and exactly at
each detected time discontinuity,
the time at one day less than the highest possible time value,
and the time at the highest possible time value,
Each line ends with
.B isdst=1
if the given time is Daylight Saving Time or
.B isdst=0
otherwise.
.TP
.BI "\-c " [loyear,]hiyear
Cut off verbose output near the start of the given year(s).
By default,
the program cuts off verbose output near the starts of the years -500 and 2500.
.SH LIMITATIONS
The
.B \-v
option may not be used on systems with floating-point time_t values
that are neither float nor double.
.PP
Time discontinuities are found by sampling the results returned by localtime
at twelve-hour intervals.
This works in all real-world cases;
one can construct artificial time zones for which this fails.
.SH "SEE ALSO"
newctime(3), tzfile(5), zic(8)
.\" @(#)zdump.8 7.7

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.TH ZIC 8
.SH NAME
zic \- time zone compiler
.SH SYNOPSIS
.B zic
[
.B \-\-version
]
[
.B \-v
] [
.B \-d
.I directory
] [
.B \-l
.I localtime
] [
.B \-p
.I posixrules
] [
.B \-L
.I leapsecondfilename
] [
.B \-s
] [
.B \-y
.I command
] [
.I filename
\&... ]
.SH DESCRIPTION
.if t .ds lq ``
.if t .ds rq ''
.if n .ds lq \&"\"
.if n .ds rq \&"\"
.de q
\\$3\*(lq\\$1\*(rq\\$2
..
.I Zic
reads text from the file(s) named on the command line
and creates the time conversion information files specified in this input.
If a
.I filename
is
.BR \- ,
the standard input is read.
.PP
These options are available:
.TP
.BI "\-\-version"
Output version information and exit.
.TP
.BI "\-d " directory
Create time conversion information files in the named directory rather than
in the standard directory named below.
.TP
.BI "\-l " timezone
Use the given time zone as local time.
.I Zic
will act as if the input contained a link line of the form
.sp
.ti +.5i
Link \fItimezone\fP localtime
.TP
.BI "\-p " timezone
Use the given time zone's rules when handling POSIX-format
time zone environment variables.
.I Zic
will act as if the input contained a link line of the form
.sp
.ti +.5i
Link \fItimezone\fP posixrules
.TP
.BI "\-L " leapsecondfilename
Read leap second information from the file with the given name.
If this option is not used,
no leap second information appears in output files.
.TP
.B \-v
Complain if a year that appears in a data file is outside the range
of years representable by
.IR time (2)
values.
Also complain if a time of 24:00
(which cannot be handled by pre-1998 versions of
.IR zic )
appears in the input.
.TP
.B \-s
Limit time values stored in output files to values that are the same
whether they're taken to be signed or unsigned.
You can use this option to generate SVVS-compatible files.
.TP
.BI "\-y " command
Use the given
.I command
rather than
.B yearistype
when checking year types (see below).
.PP
Input lines are made up of fields.
Fields are separated from one another by any number of white space characters.
Leading and trailing white space on input lines is ignored.
An unquoted sharp character (#) in the input introduces a comment which extends
to the end of the line the sharp character appears on.
White space characters and sharp characters may be enclosed in double quotes
(") if they're to be used as part of a field.
Any line that is blank (after comment stripping) is ignored.
Non-blank lines are expected to be of one of three types:
rule lines, zone lines, and link lines.
.PP
A rule line has the form
.nf
.ti +.5i
.ta \w'Rule\0\0'u +\w'NAME\0\0'u +\w'FROM\0\0'u +\w'1973\0\0'u +\w'TYPE\0\0'u +\w'Apr\0\0'u +\w'lastSun\0\0'u +\w'2:00\0\0'u +\w'SAVE\0\0'u
.sp
Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S
.sp
For example:
.ti +.5i
.sp
Rule US 1967 1973 \- Apr lastSun 2:00 1:00 D
.sp
.fi
The fields that make up a rule line are:
.TP "\w'LETTER/S'u"
.B NAME
Gives the (arbitrary) name of the set of rules this rule is part of.
.TP
.B FROM
Gives the first year in which the rule applies.
Any integer year can be supplied; the Gregorian calendar is assumed.
The word
.B minimum
(or an abbreviation) means the minimum year representable as an integer.
The word
.B maximum
(or an abbreviation) means the maximum year representable as an integer.
Rules can describe times that are not representable as time values,
with the unrepresentable times ignored; this allows rules to be portable
among hosts with differing time value types.
.TP
.B TO
Gives the final year in which the rule applies.
In addition to
.B minimum
and
.B maximum
(as above),
the word
.B only
(or an abbreviation)
may be used to repeat the value of the
.B FROM
field.
.TP
.B TYPE
Gives the type of year in which the rule applies.
If
.B TYPE
is
.B \-
then the rule applies in all years between
.B FROM
and
.B TO
inclusive.
If
.B TYPE
is something else, then
.I zic
executes the command
.ti +.5i
\fByearistype\fP \fIyear\fP \fItype\fP
.br
to check the type of a year:
an exit status of zero is taken to mean that the year is of the given type;
an exit status of one is taken to mean that the year is not of the given type.
.TP
.B IN
Names the month in which the rule takes effect.
Month names may be abbreviated.
.TP
.B ON
Gives the day on which the rule takes effect.
Recognized forms include:
.nf
.in +.5i
.sp
.ta \w'Sun<=25\0\0'u
5 the fifth of the month
lastSun the last Sunday in the month
lastMon the last Monday in the month
Sun>=8 first Sunday on or after the eighth
Sun<=25 last Sunday on or before the 25th
.fi
.in -.5i
.sp
Names of days of the week may be abbreviated or spelled out in full.
Note that there must be no spaces within the
.B ON
field.
.TP
.B AT
Gives the time of day at which the rule takes effect.
Recognized forms include:
.nf
.in +.5i
.sp
.ta \w'1:28:13\0\0'u
2 time in hours
2:00 time in hours and minutes
15:00 24-hour format time (for times after noon)
1:28:14 time in hours, minutes, and seconds
\- equivalent to 0
.fi
.in -.5i
.sp
where hour 0 is midnight at the start of the day,
and hour 24 is midnight at the end of the day.
Any of these forms may be followed by the letter
.B w
if the given time is local
.q "wall clock"
time,
.B s
if the given time is local
.q standard
time, or
.B u
(or
.B g
or
.BR z )
if the given time is universal time;
in the absence of an indicator,
wall clock time is assumed.
.TP
.B SAVE
Gives the amount of time to be added to local standard time when the rule is in
effect.
This field has the same format as the
.B AT
field
(although, of course, the
.B w
and
.B s
suffixes are not used).
.TP
.B LETTER/S
Gives the
.q "variable part"
(for example, the
.q S
or
.q D
in
.q EST
or
.q EDT )
of time zone abbreviations to be used when this rule is in effect.
If this field is
.BR \- ,
the variable part is null.
.PP
A zone line has the form
.sp
.nf
.ti +.5i
.ta \w'Zone\0\0'u +\w'Australia/Adelaide\0\0'u +\w'GMTOFF\0\0'u +\w'RULES/SAVE\0\0'u +\w'FORMAT\0\0'u
Zone NAME GMTOFF RULES/SAVE FORMAT [UNTIL]
.sp
For example:
.sp
.ti +.5i
Zone Australia/Adelaide 9:30 Aus CST 1971 Oct 31 2:00
.sp
.fi
The fields that make up a zone line are:
.TP "\w'GMTOFF'u"
.B NAME
The name of the time zone.
This is the name used in creating the time conversion information file for the
zone.
.TP
.B GMTOFF
The amount of time to add to UTC to get standard time in this zone.
This field has the same format as the
.B AT
and
.B SAVE
fields of rule lines;
begin the field with a minus sign if time must be subtracted from UTC.
.TP
.B RULES/SAVE
The name of the rule(s) that apply in the time zone or,
alternately, an amount of time to add to local standard time.
If this field is
.B \-
then standard time always applies in the time zone.
.TP
.B FORMAT
The format for time zone abbreviations in this time zone.
The pair of characters
.B %s
is used to show where the
.q "variable part"
of the time zone abbreviation goes.
Alternately,
a slash (/)
separates standard and daylight abbreviations.
.TP
.B UNTIL
The time at which the UTC offset or the rule(s) change for a location.
It is specified as a year, a month, a day, and a time of day.
If this is specified,
the time zone information is generated from the given UTC offset
and rule change until the time specified.
The month, day, and time of day have the same format as the IN, ON, and AT
columns of a rule; trailing columns can be omitted, and default to the
earliest possible value for the missing columns.
.IP
The next line must be a
.q continuation
line; this has the same form as a zone line except that the
string
.q Zone
and the name are omitted, as the continuation line will
place information starting at the time specified as the
.B UNTIL
field in the previous line in the file used by the previous line.
Continuation lines may contain an
.B UNTIL
field, just as zone lines do, indicating that the next line is a further
continuation.
.PP
A link line has the form
.sp
.nf
.ti +.5i
.ta \w'Link\0\0'u +\w'Europe/Istanbul\0\0'u
Link LINK-FROM LINK-TO
.sp
For example:
.sp
.ti +.5i
Link Europe/Istanbul Asia/Istanbul
.sp
.fi
The
.B LINK-FROM
field should appear as the
.B NAME
field in some zone line;
the
.B LINK-TO
field is used as an alternate name for that zone.
.PP
Except for continuation lines,
lines may appear in any order in the input.
.PP
Lines in the file that describes leap seconds have the following form:
.nf
.ti +.5i
.ta \w'Leap\0\0'u +\w'YEAR\0\0'u +\w'MONTH\0\0'u +\w'DAY\0\0'u +\w'HH:MM:SS\0\0'u +\w'CORR\0\0'u
.sp
Leap YEAR MONTH DAY HH:MM:SS CORR R/S
.sp
For example:
.ti +.5i
.sp
Leap 1974 Dec 31 23:59:60 + S
.sp
.fi
The
.BR YEAR ,
.BR MONTH ,
.BR DAY ,
and
.B HH:MM:SS
fields tell when the leap second happened.
The
.B CORR
field
should be
.q +
if a second was added
or
.q -
if a second was skipped.
.\" There's no need to document the following, since it's impossible for more
.\" than one leap second to be inserted or deleted at a time.
.\" The C Standard is in error in suggesting the possibility.
.\" See Terry J Quinn, The BIPM and the accurate measure of time,
.\" Proc IEEE 79, 7 (July 1991), 894-905.
.\" or
.\" .q ++
.\" if two seconds were added
.\" or
.\" .q --
.\" if two seconds were skipped.
The
.B R/S
field
should be (an abbreviation of)
.q Stationary
if the leap second time given by the other fields should be interpreted as UTC
or
(an abbreviation of)
.q Rolling
if the leap second time given by the other fields should be interpreted as
local wall clock time.
.SH NOTES
For areas with more than two types of local time,
you may need to use local standard time in the
.B AT
field of the earliest transition time's rule to ensure that
the earliest transition time recorded in the compiled file is correct.
.PP
If,
for a particular zone,
a clock advance caused by the start of daylight saving
coincides with and is equal to
a clock retreat caused by a change in UTC offset,
.IR zic
produces a single transition to daylight saving at the new UTC offset
(without any change in wall clock time).
To get separate transitions
use multiple zone continuation lines
specifying transition instants using universal time.
.SH FILE
/usr/share/zoneinfo standard directory used for created files
.SH "SEE ALSO"
newctime(3), tzfile(5), zdump(8)
.\" @(#)zic.8 7.24

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.TH NEWCTIME 3
.SH NAME
asctime, ctime, difftime, gmtime, localtime, mktime \- convert date and time to ASCII
.SH SYNOPSIS
.nf
.B extern char *tzname[2];
.PP
.B void tzset()
.PP
.B #include <sys/types.h>
.PP
.B char *ctime(clock)
.B const time_t *clock;
.PP
.B double difftime(time1, time0)
.B time_t time1;
.B time_t time0;
.PP
.B #include <time.h>
.PP
.B char *asctime(tm)
.B const struct tm *tm;
.PP
.B struct tm *localtime(clock)
.B const time_t *clock;
.PP
.B struct tm *gmtime(clock)
.B const time_t *clock;
.PP
.B time_t mktime(tm)
.B struct tm *tm;
.PP
.B cc ... -ltz
.fi
.SH DESCRIPTION
.I Ctime\^
converts a long integer, pointed to by
.IR clock ,
representing the time in seconds since
00:00:00 UTC, 1970-01-01,
and returns a pointer to a
string of the form
.br
.ce
.eo
Thu Nov 24 18:22:48 1986\n\0
.br
.ec
Years requiring fewer than four characters are padded with leading zeroes.
For years longer than four characters, the string is of the form
.br
.ce
.eo
Thu Nov 24 18:22:48 81986\n\0
.ec
.br
with five spaces before the year.
These unusual formats are designed to make it less likely that older
software that expects exactly 26 bytes of output will mistakenly output
misleading values for out-of-range years.
.PP
.I Localtime\^
and
.I gmtime\^
return pointers to ``tm'' structures, described below.
.I Localtime\^
corrects for the time zone and any time zone adjustments
(such as Daylight Saving Time in the United States).
After filling in the ``tm'' structure,
.I localtime
sets the
.BR tm_isdst 'th
element of
.B tzname
to a pointer to an
ASCII string that's the time zone abbreviation to be used with
.IR localtime 's
return value.
.PP
.I Gmtime\^
converts to Coordinated Universal Time.
.PP
.I Asctime\^
converts a time value contained in a
``tm'' structure to a string,
as shown in the above example,
and returns a pointer to the string.
.PP
.I Mktime\^
converts the broken-down time,
expressed as local time,
in the structure pointed to by
.I tm
into a calendar time value with the same encoding as that of the values
returned by the
.I time
function.
The original values of the
.B tm_wday
and
.B tm_yday
components of the structure are ignored,
and the original values of the other components are not restricted
to their normal ranges.
(A positive or zero value for
.B tm_isdst
causes
.I mktime
to presume initially that summer time (for example, Daylight Saving Time
in the U.S.A.)
respectively,
is or is not in effect for the specified time.
A negative value for
.B tm_isdst
causes the
.I mktime
function to attempt to divine whether summer time is in effect
for the specified time.)
On successful completion, the values of the
.B tm_wday
and
.B tm_yday
components of the structure are set appropriately,
and the other components are set to represent the specified calendar time,
but with their values forced to their normal ranges; the final value of
.B tm_mday
is not set until
.B tm_mon
and
.B tm_year
are determined.
.I Mktime\^
returns the specified calendar time;
If the calendar time cannot be represented,
it returns
.BR -1 .
.PP
.I Difftime\^
returns the difference between two calendar times,
.RI ( time1
-
.IR time0 ),
expressed in seconds.
.PP
Declarations of all the functions and externals, and the ``tm'' structure,
are in the
.B <time.h>\^
header file.
The structure (of type)
.B struct tm
includes the following fields:
.RS
.PP
.nf
.ta .5i +\w'long tm_gmtoff;\0\0'u
int tm_sec; /\(** seconds (0 - 60) \(**/
int tm_min; /\(** minutes (0 - 59) \(**/
int tm_hour; /\(** hours (0 - 23) \(**/
int tm_mday; /\(** day of month (1 - 31) \(**/
int tm_mon; /\(** month of year (0 - 11) \(**/
int tm_year; /\(** year \- 1900 \(**/
int tm_wday; /\(** day of week (Sunday = 0) \(**/
int tm_yday; /\(** day of year (0 - 365) \(**/
int tm_isdst; /\(** is summer time in effect? \(**/
char \(**tm_zone; /\(** abbreviation of timezone name \(**/
long tm_gmtoff; /\(** offset from UTC in seconds \(**/
.fi
.RE
.PP
The
.I tm_zone
and
.I tm_gmtoff
fields exist, and are filled in, only if arrangements to do
so were made when the library containing these functions was
created.
There is no guarantee that these fields will continue to exist
in this form in future releases of this code.
.PP
.I Tm_isdst\^
is non-zero if summer time is in effect.
.PP
.I Tm_gmtoff
is the offset (in seconds) of the time represented
from UTC, with positive values indicating east
of the Prime Meridian.
.SH FILES
.ta \w'/usr/share/zoneinfo/posixrules\0\0'u
/usr/share/zoneinfo time zone information directory
.br
/usr/share/zoneinfo/localtime local time zone file
.br
/usr/share/zoneinfo/posixrules used with POSIX-style TZ's
.br
/usr/share/zoneinfo/GMT for UTC leap seconds
.sp
If
.B /usr/share/zoneinfo/GMT
is absent,
UTC leap seconds are loaded from
.BR /usr/share/zoneinfo/posixrules .
.SH SEE ALSO
getenv(3),
newstrftime(3),
newtzset(3),
time(2),
tzfile(5)
.SH NOTES
The return values point to static data;
the data is overwritten by each call.
The
.B tm_zone
field of a returned
.B "struct tm"
points to a static array of characters, which
will also be overwritten at the next call
(and by calls to
.IR tzset ).
.PP
.I Asctime\^
and
.I ctime\^
behave strangely for years before 1000 or after 9999.
The 1989 and 1999 editions of the C Standard say
that years from \-99 through 999 are converted without
extra spaces, but this conflicts with longstanding
tradition and with this implementation.
Traditional implementations of these two functions are
restricted to years in the range 1900 through 2099.
To avoid this portability mess, new programs should use
.I strftime\^
instead.
.PP
Avoid using out-of-range values with
.I mktime
when setting up lunch with promptness sticklers in Riyadh.
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.\" Based on the UCB file whose copyright information appears below.
.\" Copyright (c) 1989, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" from: @(#)strftime.3 5.12 (Berkeley) 6/29/91
.\" $Id: strftime.3,v 1.4 1993/12/15 20:33:00 jtc Exp $
.\"
.TH NEWSTRFTIME 3
.SH NAME
strftime \- format date and time
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <time.h>
.PP
.B size_t strftime(buf, maxsize, format, timeptr)
.B char *buf;
.B size_t maxsize;
.B const char *format;
.B const struct tm *timeptr
.PP
.B cc ... -ltz
.fi
.SH DESCRIPTION
The
.I strftime\^
function formats the information from
.I timeptr\^
into the buffer
.I buf\^
according to the string pointed to by
.IR format\^ .
.PP
The
.I format\^
string consists of zero or more conversion specifications and
ordinary characters.
All ordinary characters are copied directly into the buffer.
A conversion specification consists of a percent sign
.Ql %
and one other character.
.PP
No more than
.I maxsize\^
characters are be placed into the array.
If the total number of resulting characters, including the terminating
null character, is not more than
.IR maxsize\^ ,
.I strftime\^
returns the number of characters in the array, not counting the
terminating null.
Otherwise, zero is returned.
.PP
Each conversion specification is replaced by the characters as
follows which are then copied into the buffer.
.TP
%A
is replaced by the locale's full weekday name.
.TP
%a
is replaced by the locale's abbreviated weekday name.
.TP
%B
is replaced by the locale's full month name.
.TP
%b or %h
is replaced by the locale's abbreviated month name.
.TP
%C
is replaced by the century (a year divided by 100 and truncated to an integer)
as a decimal number (00-99).
.TP
%c
is replaced by the locale's appropriate date and time representation.
.TP
%D
is replaced by the date in the format %m/%d/%y.
.TP
%d
is replaced by the day of the month as a decimal number (01-31).
.TP
%e
is replaced by the day of month as a decimal number (1-31);
single digits are preceded by a blank.
.TP
%F
is replaced by the date in the format %Y-%m-%d.
.TP
%G
is replaced by the ISO 8601 year with century as a decimal number.
.TP
%g
is replaced by the ISO 8601 year without century as a decimal number (00-99).
.TP
%H
is replaced by the hour (24-hour clock) as a decimal number (00-23).
.TP
%I
is replaced by the hour (12-hour clock) as a decimal number (01-12).
.TP
%j
is replaced by the day of the year as a decimal number (001-366).
.TP
%k
is replaced by the hour (24-hour clock) as a decimal number (0-23);
single digits are preceded by a blank.
.TP
%l
is replaced by the hour (12-hour clock) as a decimal number (1-12);
single digits are preceded by a blank.
.TP
%M
is replaced by the minute as a decimal number (00-59).
.TP
%m
is replaced by the month as a decimal number (01-12).
.TP
%n
is replaced by a newline.
.TP
%p
is replaced by the locale's equivalent of either AM or PM.
.TP
%R
is replaced by the time in the format %H:%M.
.TP
%r
is replaced by the locale's representation of 12-hour clock time
using AM/PM notation.
.TP
%S
is replaced by the second as a decimal number (00-60).
.TP
%s
is replaced by the number of seconds since the Epoch, UTC (see mktime(3)).
.TP
%T
is replaced by the time in the format %H:%M:%S.
.TP
%t
is replaced by a tab.
.TP
%U
is replaced by the week number of the year (Sunday as the first day of
the week) as a decimal number (00-53).
.TP
%u
is replaced by the weekday (Monday as the first day of the week)
as a decimal number (1-7).
.TP
%V
is replaced by the week number of the year (Monday as the first day of
the week) as a decimal number (01-53). If the week containing January
1 has four or more days in the new year, then it is week 1; otherwise
it is week 53 of the previous year, and the next week is week 1.
.TP
%W
is replaced by the week number of the year (Monday as the first day of
the week) as a decimal number (00-53).
.TP
%w
is replaced by the weekday (Sunday as the first day of the week)
as a decimal number (0-6).
.TP
%X
is replaced by the locale's appropriate time representation.
.TP
%x
is replaced by the locale's appropriate date representation.
.TP
%Y
is replaced by the year with century as a decimal number.
.TP
%y
is replaced by the year without century as a decimal number (00-99).
.TP
%Z
is replaced by the time zone name,
or by the empty string if this is not determinable.
.TP
%z
is replaced by the offset from UTC in the format +HHMM or -HHMM as appropriate,
with positive values representing locations east of Greenwich,
or by the empty string if this is not determinable.
.TP
%%
is replaced by a single %.
.TP
%+
is replaced by the date and time in date(1) format.
.SH SEE ALSO
date(1),
getenv(3),
newctime(3),
newtzset(3),
time(2),
tzfile(5)
.\" @(#)newstrftime.3 7.15

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.TH NEWTZSET 3
.SH NAME
tzset \- initialize time conversion information
.SH SYNOPSIS
.nf
.B void tzset()
.PP
.B cc ... -ltz
.fi
.SH DESCRIPTION
.I Tzset
uses the value of the environment variable
.B TZ
to set time conversion information used by
.IR localtime .
If
.B TZ
does not appear in the environment,
the best available approximation to local wall clock time, as specified
by the
.IR tzfile (5)-format
file
.B localtime
in the system time conversion information directory, is used by
.IR localtime .
If
.B TZ
appears in the environment but its value is a null string,
Coordinated Universal Time (UTC) is used (without leap second
correction). If
.B TZ
appears in the environment and its value is not a null string:
.IP
if the value begins with a colon, it is used as a pathname of a file
from which to read the time conversion information;
.IP
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 specification of
the time conversion information.
.PP
When
.B 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 information
directory.
The file must be in the format specified in
.IR tzfile (5).
.PP
When
.B TZ
is used directly as a specification of the time conversion information,
it must have the following syntax (spaces inserted for clarity):
.IP
\fIstd\|offset\fR[\fIdst\fR[\fIoffset\fR][\fB,\fIrule\fR]]
.PP
Where:
.RS
.TP 15
.IR std " and " dst
Three or more bytes that are the designation for the standard
.RI ( std )
or summer
.RI ( dst )
time zone. Only
.I std
is required; if
.I 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
.RB ( : ),
digits, comma
.RB ( , ),
minus
.RB ( \(mi ),
plus
.RB ( \(pl ),
and ASCII NUL are allowed.
.TP
.I offset
Indicates the value one must add to the local time to arrive at
Coordinated Universal Time. The
.I offset
has the form:
.RS
.IP
\fIhh\fR[\fB:\fImm\fR[\fB:\fIss\fR]]
.RE
.IP
The minutes
.RI ( mm )
and seconds
.RI ( ss )
are optional. The hour
.RI ( hh )
is required and may be a single digit. The
.I offset
following
.I std
is required. If no
.I offset
follows
.IR 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) \(em if present \(em between zero and 59. If preceded by a
.RB `` \(mi '',
the time zone shall be east of the Prime Meridian; otherwise it shall be
west (which may be indicated by an optional preceding
.RB `` \(pl '').
.TP
.I rule
Indicates when to change to and back from summer time. The
.I rule
has the form:
.RS
.IP
\fIdate\fB/\fItime\fB,\fIdate\fB/\fItime\fR
.RE
.IP
where the first
.I date
describes when the change from standard to summer time occurs and the
second
.I date
describes when the change back happens. Each
.I time
field describes when, in current local time, the change to the other
time is made.
.IP
The format of
.I date
is one of the following:
.RS
.TP 10
.BI J n
The Julian day
.I n
.RI "(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.
.TP
.I n
The zero-based Julian day
.RI "(0\ \(<=" "\ n\ " "\(<=\ 365).
Leap days are counted, and it is possible to refer to February 29.
.TP
.BI M m . n . d
The
.IR d' th
day
.RI "(0\ \(<=" "\ d\ " "\(<=\ 6)
of week
.I n
of month
.I m
of the year
.RI "(1\ \(<=" "\ n\ " "\(<=\ 5,
.RI "1\ \(<=" "\ m\ " "\(<=\ 12,
where week 5 means ``the last
.I d
day in month
.IR m ''
which may occur in either the fourth or the fifth week). Week 1 is the
first week in which the
.IR d' th
day occurs. Day zero is Sunday.
.RE
.IP "" 15
The
.I time
has the same format as
.I offset
except that no leading sign
.RB (`` \(mi ''
or
.RB `` \(pl '')
is allowed. The default, if
.I time
is not given, is
.BR 02:00:00 .
.RE
.LP
If no
.I rule
is present in
.BR TZ ,
the rules specified
by the
.IR tzfile (5)-format
file
.B 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
.I offset
values in
.BR TZ .
.PP
For compatibility with System V Release 3.1, a semicolon
.RB ( ; )
may be used to separate the
.I rule
from the rest of the specification.
.PP
If the
.B TZ
environment variable does not specify a
.IR tzfile (5)-format
and cannot be interpreted as a direct specification,
UTC is used.
.SH FILES
.ta \w'/usr/share/zoneinfo/posixrules\0\0'u
/usr/share/zoneinfo time zone information directory
.br
/usr/share/zoneinfo/localtime local time zone file
.br
/usr/share/zoneinfo/posixrules used with POSIX-style TZ's
.br
/usr/share/zoneinfo/GMT for UTC leap seconds
.sp
If
.B /usr/share/zoneinfo/GMT
is absent,
UTC leap seconds are loaded from
.BR /usr/share/zoneinfo/posixrules .
.SH SEE ALSO
getenv(3),
newctime(3),
newstrftime(3),
time(2),
tzfile(5)
.\" @(#)newtzset.3 7.5

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.TH TIME2POSIX 3
.SH NAME
time2posix, posix2time \- convert seconds since the Epoch
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <time.h>
.PP
.B time_t time2posix(t)
.B time_t t
.PP
.B time_t posix2time(t)
.B time_t t
.PP
.B cc ... -ltz
.fi
.SH DESCRIPTION
IEEE Standard 1003.1
(POSIX)
legislates that a time_t value of
536457599 shall correspond to "Wed Dec 31 23:59:59 UTC 1986."
This effectively implies that POSIX time_t's cannot include leap
seconds and,
therefore,
that the system time must be adjusted as each leap occurs.
.PP
If the time package is configured with leap-second support
enabled,
however,
no such adjustment is needed and
time_t values continue to increase over leap events
(as a true `seconds since...' value).
This means that these values will differ from those required by POSIX
by the net number of leap seconds inserted since the Epoch.
.PP
Typically this is not a problem as the type time_t is intended
to be
(mostly)
opaque\(emtime_t values should only be obtained-from and
passed-to functions such as
.IR time(2) ,
.IR localtime(3) ,
.IR mktime(3) ,
and
.IR difftime(3) .
However,
POSIX gives an arithmetic
expression for directly computing a time_t value from a given date/time,
and the same relationship is assumed by some
(usually older)
applications.
Any programs creating/dissecting time_t's
using such a relationship will typically not handle intervals
over leap seconds correctly.
.PP
The
.I time2posix
and
.I posix2time
functions are provided to address this time_t mismatch by converting
between local time_t values and their POSIX equivalents.
This is done by accounting for the number of time-base changes that
would have taken place on a POSIX system as leap seconds were inserted
or deleted.
These converted values can then be used in lieu of correcting the older
applications,
or when communicating with POSIX-compliant systems.
.PP
.I Time2posix
is single-valued.
That is,
every local time_t
corresponds to a single POSIX time_t.
.I Posix2time
is less well-behaved:
for a positive leap second hit the result is not unique,
and for a negative leap second hit the corresponding
POSIX time_t doesn't exist so an adjacent value is returned.
Both of these are good indicators of the inferiority of the
POSIX representation.
.PP
The following table summarizes the relationship between a time
T and it's conversion to,
and back from,
the POSIX representation over the leap second inserted at the end of June,
1993.
.nf
.ta \w'93/06/30 'u +\w'23:59:59 'u +\w'A+0 'u +\w'X=time2posix(T) 'u
DATE TIME T X=time2posix(T) posix2time(X)
93/06/30 23:59:59 A+0 B+0 A+0
93/06/30 23:59:60 A+1 B+1 A+1 or A+2
93/07/01 00:00:00 A+2 B+1 A+1 or A+2
93/07/01 00:00:01 A+3 B+2 A+3
A leap second deletion would look like...
DATE TIME T X=time2posix(T) posix2time(X)
??/06/30 23:59:58 A+0 B+0 A+0
??/07/01 00:00:00 A+1 B+2 A+1
??/07/01 00:00:01 A+2 B+3 A+2
.sp
.ce
[Note: posix2time(B+1) => A+0 or A+1]
.fi
.PP
If leap-second support is not enabled,
local time_t's and
POSIX time_t's are equivalent,
and both
.I time2posix
and
.I posix2time
degenerate to the identity function.
.SH SEE ALSO
difftime(3),
localtime(3),
mktime(3),
time(2)
.\" @(#)time2posix.3 7.8
.\" This file is in the public domain, so clarified as of
.\" 1996-06-05 by Arthur David Olson.

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.TH TZFILE 5
.SH NAME
tzfile \- time zone information
.SH SYNOPSIS
.B
#include <tzfile.h>
.SH DESCRIPTION
The time zone information files used by
.IR tzset (3)
begin with the magic characters "TZif" to identify then as
time zone information files,
followed by sixteen bytes reserved for future use,
followed by six four-byte values of type
.BR long ,
written in a ``standard'' byte order
(the high-order byte of the value is written first).
These values are,
in order:
.TP
.I tzh_ttisgmtcnt
The number of UTC/local indicators stored in the file.
.TP
.I tzh_ttisstdcnt
The number of standard/wall indicators stored in the file.
.TP
.I tzh_leapcnt
The number of leap seconds for which data is stored in the file.
.TP
.I tzh_timecnt
The number of "transition times" for which data is stored
in the file.
.TP
.I tzh_typecnt
The number of "local time types" for which data is stored
in the file (must not be zero).
.TP
.I tzh_charcnt
The number of characters of "time zone abbreviation strings"
stored in the file.
.PP
The above header is followed by
.I tzh_timecnt
four-byte values of type
.BR long ,
sorted in ascending order.
These values are written in ``standard'' byte order.
Each is used as a transition time (as returned by
.IR time (2))
at which the rules for computing local time change.
Next come
.I tzh_timecnt
one-byte values of type
.BR "unsigned char" ;
each one tells which of the different types of ``local time'' types
described in the file is associated with the same-indexed transition time.
These values serve as indices into an array of
.I ttinfo
structures that appears next in the file;
these structures are defined as follows:
.in +.5i
.sp
.nf
.ta .5i +\w'unsigned int\0\0'u
struct ttinfo {
long tt_gmtoff;
int tt_isdst;
unsigned int tt_abbrind;
};
.in -.5i
.fi
.sp
Each structure is written as a four-byte value for
.I tt_gmtoff
of type
.BR long ,
in a standard byte order, followed by a one-byte value for
.I tt_isdst
and a one-byte value for
.IR tt_abbrind .
In each structure,
.I tt_gmtoff
gives the number of seconds to be added to UTC,
.I tt_isdst
tells whether
.I tm_isdst
should be set by
.I localtime (3)
and
.I tt_abbrind
serves as an index into the array of time zone abbreviation characters
that follow the
.I ttinfo
structure(s) in the file.
.PP
Then there are
.I tzh_leapcnt
pairs of four-byte values, written in standard byte order;
the first value of each pair gives the time
(as returned by
.IR time(2))
at which a leap second occurs;
the second gives the
.I total
number of leap seconds to be applied after the given time.
The pairs of values are sorted in ascending order by time.
.PP
Then there are
.I tzh_ttisstdcnt
standard/wall indicators, each stored as a one-byte value;
they tell whether the transition times associated with local time types
were specified as standard time or wall clock time,
and are used when a time zone file is used in handling POSIX-style
time zone environment variables.
.PP
Finally there are
.I tzh_ttisgmtcnt
UTC/local indicators, each stored as a one-byte value;
they tell whether the transition times associated with local time types
were specified as UTC or local time,
and are used when a time zone file is used in handling POSIX-style
time zone environment variables.
.PP
.I Localtime
uses the first standard-time
.I ttinfo
structure in the file
(or simply the first
.I ttinfo
structure in the absence of a standard-time structure)
if either
.I tzh_timecnt
is zero or the time argument is less than the first transition time recorded
in the file.
.SH SEE ALSO
newctime(3)
.\" @(#)tzfile.5 7.12
.\" This file is in the public domain, so clarified as of
.\" 1996-06-05 by Arthur David Olson.

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.TH TZSELECT 8
.SH NAME
tzselect \- select a time zone
.SH SYNOPSIS
.B tzselect
.SH DESCRIPTION
The
.B tzselect
program asks the user for information about the current location,
and outputs the resulting time zone description to standard output.
The output is suitable as a value for the TZ environment variable.
.PP
All interaction with the user is done via standard input and standard error.
.SH "ENVIRONMENT VARIABLES"
.TP
\f3AWK\fP
Name of a Posix-compliant
.I awk
program (default:
.BR awk ).
.TP
\f3TZDIR\fP
Name of the directory containing time zone data files (default:
.BR /usr/share/zoneinfo ).
.SH FILES
.TP
\f2TZDIR\fP\f3/iso3166.tab\fP
Table of ISO 3166 2-letter country codes and country names.
.TP
\f2TZDIR\fP\f3/zone.tab\fP
Table of country codes, latitude and longitude, TZ values, and
descriptive comments.
.TP
\f2TZDIR\fP\f3/\fP\f2TZ\fP
Time zone data file for time zone \f2TZ\fP.
.SH "EXIT STATUS"
The exit status is zero if a time zone was successfully obtained from the user,
nonzero otherwise.
.SH "SEE ALSO"
newctime(3), tzfile(5), zdump(8), zic(8)
.\" @(#)tzselect.8 1.3

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.TH ZDUMP 8
.SH NAME
zdump \- time zone dumper
.SH SYNOPSIS
.B zdump
[
.B \-\-version
]
[
.B \-v
] [
.B \-c
[loyear,]hiyear ] [ zonename ... ]
.SH DESCRIPTION
.I Zdump
prints the current time in each
.I zonename
named on the command line.
.PP
These options are available:
.TP
.BI "\-\-version"
Output version information and exit.
.TP
.B \-v
For each
.I zonename
on the command line,
print the time at the lowest possible time value,
the time one day after the lowest possible time value,
the times both one second before and exactly at
each detected time discontinuity,
the time at one day less than the highest possible time value,
and the time at the highest possible time value,
Each line ends with
.B isdst=1
if the given time is Daylight Saving Time or
.B isdst=0
otherwise.
.TP
.BI "\-c " [loyear,]hiyear
Cut off verbose output near the start of the given year(s).
By default,
the program cuts off verbose output near the starts of the years -500 and 2500.
.SH LIMITATIONS
The
.B \-v
option may not be used on systems with floating-point time_t values
that are neither float nor double.
.PP
Time discontinuities are found by sampling the results returned by localtime
at twelve-hour intervals.
This works in all real-world cases;
one can construct artificial time zones for which this fails.
.SH "SEE ALSO"
newctime(3), tzfile(5), zic(8)
.\" @(#)zdump.8 7.7

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.TH ZIC 8
.SH NAME
zic \- time zone compiler
.SH SYNOPSIS
.B zic
[
.B \-\-version
]
[
.B \-v
] [
.B \-d
.I directory
] [
.B \-l
.I localtime
] [
.B \-p
.I posixrules
] [
.B \-L
.I leapsecondfilename
] [
.B \-s
] [
.B \-y
.I command
] [
.I filename
\&... ]
.SH DESCRIPTION
.if t .ds lq ``
.if t .ds rq ''
.if n .ds lq \&"\"
.if n .ds rq \&"\"
.de q
\\$3\*(lq\\$1\*(rq\\$2
..
.I Zic
reads text from the file(s) named on the command line
and creates the time conversion information files specified in this input.
If a
.I filename
is
.BR \- ,
the standard input is read.
.PP
These options are available:
.TP
.BI "\-\-version"
Output version information and exit.
.TP
.BI "\-d " directory
Create time conversion information files in the named directory rather than
in the standard directory named below.
.TP
.BI "\-l " timezone
Use the given time zone as local time.
.I Zic
will act as if the input contained a link line of the form
.sp
.ti +.5i
Link \fItimezone\fP localtime
.TP
.BI "\-p " timezone
Use the given time zone's rules when handling POSIX-format
time zone environment variables.
.I Zic
will act as if the input contained a link line of the form
.sp
.ti +.5i
Link \fItimezone\fP posixrules
.TP
.BI "\-L " leapsecondfilename
Read leap second information from the file with the given name.
If this option is not used,
no leap second information appears in output files.
.TP
.B \-v
Complain if a year that appears in a data file is outside the range
of years representable by
.IR time (2)
values.
Also complain if a time of 24:00
(which cannot be handled by pre-1998 versions of
.IR zic )
appears in the input.
.TP
.B \-s
Limit time values stored in output files to values that are the same
whether they're taken to be signed or unsigned.
You can use this option to generate SVVS-compatible files.
.TP
.BI "\-y " command
Use the given
.I command
rather than
.B yearistype
when checking year types (see below).
.PP
Input lines are made up of fields.
Fields are separated from one another by any number of white space characters.
Leading and trailing white space on input lines is ignored.
An unquoted sharp character (#) in the input introduces a comment which extends
to the end of the line the sharp character appears on.
White space characters and sharp characters may be enclosed in double quotes
(") if they're to be used as part of a field.
Any line that is blank (after comment stripping) is ignored.
Non-blank lines are expected to be of one of three types:
rule lines, zone lines, and link lines.
.PP
A rule line has the form
.nf
.ti +.5i
.ta \w'Rule\0\0'u +\w'NAME\0\0'u +\w'FROM\0\0'u +\w'1973\0\0'u +\w'TYPE\0\0'u +\w'Apr\0\0'u +\w'lastSun\0\0'u +\w'2:00\0\0'u +\w'SAVE\0\0'u
.sp
Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S
.sp
For example:
.ti +.5i
.sp
Rule US 1967 1973 \- Apr lastSun 2:00 1:00 D
.sp
.fi
The fields that make up a rule line are:
.TP "\w'LETTER/S'u"
.B NAME
Gives the (arbitrary) name of the set of rules this rule is part of.
.TP
.B FROM
Gives the first year in which the rule applies.
Any integer year can be supplied; the Gregorian calendar is assumed.
The word
.B minimum
(or an abbreviation) means the minimum year representable as an integer.
The word
.B maximum
(or an abbreviation) means the maximum year representable as an integer.
Rules can describe times that are not representable as time values,
with the unrepresentable times ignored; this allows rules to be portable
among hosts with differing time value types.
.TP
.B TO
Gives the final year in which the rule applies.
In addition to
.B minimum
and
.B maximum
(as above),
the word
.B only
(or an abbreviation)
may be used to repeat the value of the
.B FROM
field.
.TP
.B TYPE
Gives the type of year in which the rule applies.
If
.B TYPE
is
.B \-
then the rule applies in all years between
.B FROM
and
.B TO
inclusive.
If
.B TYPE
is something else, then
.I zic
executes the command
.ti +.5i
\fByearistype\fP \fIyear\fP \fItype\fP
.br
to check the type of a year:
an exit status of zero is taken to mean that the year is of the given type;
an exit status of one is taken to mean that the year is not of the given type.
.TP
.B IN
Names the month in which the rule takes effect.
Month names may be abbreviated.
.TP
.B ON
Gives the day on which the rule takes effect.
Recognized forms include:
.nf
.in +.5i
.sp
.ta \w'Sun<=25\0\0'u
5 the fifth of the month
lastSun the last Sunday in the month
lastMon the last Monday in the month
Sun>=8 first Sunday on or after the eighth
Sun<=25 last Sunday on or before the 25th
.fi
.in -.5i
.sp
Names of days of the week may be abbreviated or spelled out in full.
Note that there must be no spaces within the
.B ON
field.
.TP
.B AT
Gives the time of day at which the rule takes effect.
Recognized forms include:
.nf
.in +.5i
.sp
.ta \w'1:28:13\0\0'u
2 time in hours
2:00 time in hours and minutes
15:00 24-hour format time (for times after noon)
1:28:14 time in hours, minutes, and seconds
\- equivalent to 0
.fi
.in -.5i
.sp
where hour 0 is midnight at the start of the day,
and hour 24 is midnight at the end of the day.
Any of these forms may be followed by the letter
.B w
if the given time is local
.q "wall clock"
time,
.B s
if the given time is local
.q standard
time, or
.B u
(or
.B g
or
.BR z )
if the given time is universal time;
in the absence of an indicator,
wall clock time is assumed.
.TP
.B SAVE
Gives the amount of time to be added to local standard time when the rule is in
effect.
This field has the same format as the
.B AT
field
(although, of course, the
.B w
and
.B s
suffixes are not used).
.TP
.B LETTER/S
Gives the
.q "variable part"
(for example, the
.q S
or
.q D
in
.q EST
or
.q EDT )
of time zone abbreviations to be used when this rule is in effect.
If this field is
.BR \- ,
the variable part is null.
.PP
A zone line has the form
.sp
.nf
.ti +.5i
.ta \w'Zone\0\0'u +\w'Australia/Adelaide\0\0'u +\w'GMTOFF\0\0'u +\w'RULES/SAVE\0\0'u +\w'FORMAT\0\0'u
Zone NAME GMTOFF RULES/SAVE FORMAT [UNTIL]
.sp
For example:
.sp
.ti +.5i
Zone Australia/Adelaide 9:30 Aus CST 1971 Oct 31 2:00
.sp
.fi
The fields that make up a zone line are:
.TP "\w'GMTOFF'u"
.B NAME
The name of the time zone.
This is the name used in creating the time conversion information file for the
zone.
.TP
.B GMTOFF
The amount of time to add to UTC to get standard time in this zone.
This field has the same format as the
.B AT
and
.B SAVE
fields of rule lines;
begin the field with a minus sign if time must be subtracted from UTC.
.TP
.B RULES/SAVE
The name of the rule(s) that apply in the time zone or,
alternately, an amount of time to add to local standard time.
If this field is
.B \-
then standard time always applies in the time zone.
.TP
.B FORMAT
The format for time zone abbreviations in this time zone.
The pair of characters
.B %s
is used to show where the
.q "variable part"
of the time zone abbreviation goes.
Alternately,
a slash (/)
separates standard and daylight abbreviations.
.TP
.B UNTIL
The time at which the UTC offset or the rule(s) change for a location.
It is specified as a year, a month, a day, and a time of day.
If this is specified,
the time zone information is generated from the given UTC offset
and rule change until the time specified.
The month, day, and time of day have the same format as the IN, ON, and AT
columns of a rule; trailing columns can be omitted, and default to the
earliest possible value for the missing columns.
.IP
The next line must be a
.q continuation
line; this has the same form as a zone line except that the
string
.q Zone
and the name are omitted, as the continuation line will
place information starting at the time specified as the
.B UNTIL
field in the previous line in the file used by the previous line.
Continuation lines may contain an
.B UNTIL
field, just as zone lines do, indicating that the next line is a further
continuation.
.PP
A link line has the form
.sp
.nf
.ti +.5i
.ta \w'Link\0\0'u +\w'Europe/Istanbul\0\0'u
Link LINK-FROM LINK-TO
.sp
For example:
.sp
.ti +.5i
Link Europe/Istanbul Asia/Istanbul
.sp
.fi
The
.B LINK-FROM
field should appear as the
.B NAME
field in some zone line;
the
.B LINK-TO
field is used as an alternate name for that zone.
.PP
Except for continuation lines,
lines may appear in any order in the input.
.PP
Lines in the file that describes leap seconds have the following form:
.nf
.ti +.5i
.ta \w'Leap\0\0'u +\w'YEAR\0\0'u +\w'MONTH\0\0'u +\w'DAY\0\0'u +\w'HH:MM:SS\0\0'u +\w'CORR\0\0'u
.sp
Leap YEAR MONTH DAY HH:MM:SS CORR R/S
.sp
For example:
.ti +.5i
.sp
Leap 1974 Dec 31 23:59:60 + S
.sp
.fi
The
.BR YEAR ,
.BR MONTH ,
.BR DAY ,
and
.B HH:MM:SS
fields tell when the leap second happened.
The
.B CORR
field
should be
.q +
if a second was added
or
.q -
if a second was skipped.
.\" There's no need to document the following, since it's impossible for more
.\" than one leap second to be inserted or deleted at a time.
.\" The C Standard is in error in suggesting the possibility.
.\" See Terry J Quinn, The BIPM and the accurate measure of time,
.\" Proc IEEE 79, 7 (July 1991), 894-905.
.\" or
.\" .q ++
.\" if two seconds were added
.\" or
.\" .q --
.\" if two seconds were skipped.
The
.B R/S
field
should be (an abbreviation of)
.q Stationary
if the leap second time given by the other fields should be interpreted as UTC
or
(an abbreviation of)
.q Rolling
if the leap second time given by the other fields should be interpreted as
local wall clock time.
.SH NOTES
For areas with more than two types of local time,
you may need to use local standard time in the
.B AT
field of the earliest transition time's rule to ensure that
the earliest transition time recorded in the compiled file is correct.
.PP
If,
for a particular zone,
a clock advance caused by the start of daylight saving
coincides with and is equal to
a clock retreat caused by a change in UTC offset,
.IR zic
produces a single transition to daylight saving at the new UTC offset
(without any change in wall clock time).
To get separate transitions
use multiple zone continuation lines
specifying transition instants using universal time.
.SH FILE
/usr/share/zoneinfo standard directory used for created files
.SH "SEE ALSO"
newctime(3), tzfile(5), zdump(8)
.\" @(#)zic.8 7.24