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.Dd January 19, 2013
.Dt PARSEDATE 3
.Os
.Sh NAME
.Nm parsedate
.Nd date parsing function
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In util.h
.Ft time_t
.Fn parsedate "const char *datestr" "const time_t *time" "const int *tzoff"
.Sh DESCRIPTION
The
.Fn parsedate
function parses a datetime from
.Ar datestr
described in English relative to an optional
.Ar time
point and an optional timezone offset in seconds specified in
.Ar tzoff .
If either
.Ar time
or
.Ar tzoff
are
.Dv NULL ,
then the current time and timezone offset are used.
.Pp
The
.Ar datestr
is a sequence of white-space separated items.
The white-space is optional the concatenated items are not ambiguous.
An empty
.Ar datestr
is equivalent to midnight today (the beginning of this day).
.Pp
The following words have the indicated numeric meanings:
.Dv last =
\-1,
.Dv this =
0,
.Dv first, next, or one =
1,
.Dv second
is unused so that it is not confused with
.Dq seconds ,
.Dv two =
2,
.Dv third or three =
3,
.Dv fourth or four =
4,
.Dv fifth or five  =
5,
.Dv sixth or six  =
6,
.Dv seventh or seven =
7,
.Dv eighth or eight =
8,
.Dv ninth or nine =
9,
.Dv tenth or ten =
10,
.Dv eleventh or eleven =
11,
.Dv twelfth or twelve =
12.
.Pp
The following words are recognized in English only:
.Dv AM ,
.Dv PM ,
.Dv a.m. ,
.Dv p.m.
.Pp
The months:
.Dv january ,
.Dv february ,
.Dv march ,
.Dv april ,
.Dv may ,
.Dv june ,
.Dv july ,
.Dv august ,
.Dv september ,
.Dv sept ,
.Dv october ,
.Dv november ,
.Dv december ,
.Pp
The days of the week:
.Dv sunday ,
.Dv monday ,
.Dv tuesday ,
.Dv tues ,
.Dv wednesday ,
.Dv wednes ,
.Dv thursday ,
.Dv thur ,
.Dv thurs ,
.Dv friday ,
.Dv saturday .
.Pp
Time units:
.Dv year ,
.Dv month ,
.Dv fortnight ,
.Dv week ,
.Dv day ,
.Dv hour ,
.Dv minute ,
.Dv min ,
.Dv second ,
.Dv sec ,
.Dv tomorrow ,
.Dv yesterday .
.Pp
Timezone names:
.Dv gmt ,
.Dv ut ,
.Dv utc ,
.Dv wet ,
.Dv bst ,
.Dv wat ,
.Dv at ,
.Dv ast ,
.Dv adt ,
.Dv est ,
.Dv edt ,
.Dv cst ,
.Dv cdt ,
.Dv mst ,
.Dv mdt ,
.Dv pst ,
.Dv pdt ,
.Dv yst ,
.Dv ydt ,
.Dv hst ,
.Dv hdt ,
.Dv cat ,
.Dv ahst ,
.Dv nt ,
.Dv idlw ,
.Dv cet ,
.Dv met ,
.Dv mewt ,
.Dv mest ,
.Dv swt ,
.Dv sst ,
.Dv fwt ,
.Dv fst ,
.Dv eet ,
.Dv bt ,
.Dv zp4 ,
.Dv zp5 ,
.Dv zp6 ,
.Dv wast ,
.Dv wadt ,
.Dv cct ,
.Dv jst ,
.Dv east ,
.Dv eadt ,
.Dv gst ,
.Dv nzt ,
.Dv nzst ,
.Dv nzdt ,
.Dv idle .
.Pp
A variety of unambiguous dates are recognized:
.Bl -tag -compact -width "20 Jun 1994"
.It 69-09-10
For years between 69-99 we assume 1900+ and for years between 0-68
we assume 2000+.
.It 2006-11-17
An ISO-8601 date.
.It 10/1/2000
October 10, 2000; the common US format.
.It 20 Jun 1994
.It 23jun2001
.It 1-sep-06
Other common abbreviations.
.It 1/11
the year can be omitted
.El
.Pp
As well as times:
.Bl -tag -compact -width 12:11:01.000012
.It 10:01
.It 10:12pm
.It 12:11:01.000012
.It 12:21-0500
.El
.Pp
Relative items are also supported:
.Bl -tag -compact -width "this thursday"
.It -1 month
.It last friday
.It one week ago
.It this thursday
.It next sunday
.It +2 years
.El
.Pp
Seconds since epoch (also known as UNIX time) are also supported:
.Bl -tag -compact -width "@735275209"
.It @735275209
Tue Apr 20 03:06:49 UTC 1993
.El
.Sh RETURN VALUES
.Fn parsedate
returns the number of seconds passed since the Epoch, or
.Dv \-1
if the date could not be parsed properly.
A non-error result of
.Dv \-1
can be distinguished from an error by setting
.Va errno
to
.Dv 0
before calling
.Fn parsedate ,
and checking the value of
.Va errno
afterwards.
.Sh SEE ALSO
.Xr date 1 ,
.Xr errno 2 ,
.Xr eeprom 8
.Sh HISTORY
The parser used in
.Fn parsedate
was originally written by Steven M. Bellovin while at the University
of North Carolina at Chapel Hill.
It was later tweaked by a couple of people on Usenet.
Completely overhauled by Rich $alz and Jim Berets in August, 1990.
.Pp
The
.Fn parsedate
function first appeared in
.Nx 4.0 .
.Sh BUGS
.Bl -tag -compact -width 1
.It 1
The
.Fn parsedate
function is not re-entrant or thread-safe.
.It 2
The
.Fn parsedate
function cannot compute days before the unix epoch (19700101).
.It 3
The
.Fn parsedate
function assumes years less than 0 mean -
.Fa year ,
years less than 70 mean 2000 +
.Fa year ,
years less than 100 mean 1900 +
.Fa year .
.El