xref: /openbsd-src/bin/date/date.1 (revision 748ccd45821db1cffbe7de3a1e71e2ff80a5720f)

.\"	$OpenBSD: date.1,v 1.72 2021/04/29 00:47:53 deraadt Exp $
.\"	$NetBSD: date.1,v 1.12 1996/03/12 04:32:37 phil Exp $
.\"
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.\" This code is derived from software contributed to Berkeley by
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.\"     @(#)date.1	8.3 (Berkeley) 4/28/95
.\"
.Dd $Mdocdate: April 29 2021 $
.Dt DATE 1
.Os
.Sh NAME
.Nm date
.Nd display or set date and time
.Sh SYNOPSIS
.Nm date
.Op Fl aju
.Op Fl f Ar pformat
.Op Fl r Ar seconds
.Op Fl z Ar output_zone
.Op Cm + Ns Ar format
.Sm off
.Oo Oo Oo Oo Oo Oo
.Ar cc Oc
.Ar yy Oc
.Ar mm Oc
.Ar dd Oc
.Ar HH Oc
.Ar MM
.Op . Ar SS
.Oc
.Sm on
.Sh DESCRIPTION
When invoked without arguments, the
.Nm
utility displays the current date and time.
Otherwise, depending on the options specified,
.Nm
will set the date and time or print it in a user-defined way.
.Pp
Changing the system date has some risks, as described in
.Xr settimeofday 2 .
Only the superuser may change the date.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl a
Use the
.Xr adjtime 2
call to gradually skew the local time to the
desired time rather than just hopping.
.It Fl f Ar pformat
Parse the specified time using
.Xr strptime 3
with a format string of
.Ar pformat .
.It Fl j
Parse the provided date and time and display the result without changing
the clock.
.It Fl r Ar seconds
Print out (in specified format) the date and time represented by
.Ar seconds
from the Epoch.
.It Fl u
Display or set the date in UTC (Coordinated Universal) time.
.It Fl z Ar output_zone
Just before printing the time, change to the specified timezone;
see the description of
.Ev TZ
below.
This can be used with
.Fl j
to easily convert time specifications from one zone to another.
.El
.Pp
An operand with a leading plus sign
.Pq Sq +
signals a user-defined format
string which specifies the format in which to display the date and time.
The format string may contain any of the conversion specifications described
in the
.Xr strftime 3
manual page, as well as any arbitrary text.
A newline
.Pq Ql \en
character is always output after the characters specified by
the format string.
The format string for the default display is:
.Bd -literal -offset indent
%a %b %e %H:%M:%S %Z %Y
.Ed
.Pp
If an operand does not have a leading plus sign, it is interpreted as
a value for setting the system's notion of the current date and time.
The canonical representation for setting the date and time is:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Ar ccyy
Year.
If yy is specified, but cc is not,
a value for yy between 69 and 99 results in a cc value of 19.
Otherwise, a cc value of 20 is used.
.It Ar mm
Month:
a number from 1 to 12.
.It Ar dd
Day:
a number from 1 to 31.
.It Ar HH
Hour:
a number from 0 to 23.
.It Ar MM
Minute:
a number from 0 to 59.
.It Ar SS
Second:
a number from 0 to 60
(permitting a leap second),
preceded by a period.
.El
.Pp
Everything but the minute is optional.
.Pp
Time changes for Daylight Saving Time, standard time, leap seconds,
and leap years are handled automatically.
.Sh ENVIRONMENT
.Bl -tag -width Ds
.It Ev TZ
The time zone to use when parsing or displaying dates.
It is normally specified as a pathname relative to
.Pa /usr/share/zoneinfo ,
though see
.Xr tzset 3
for more information.
If this variable is not set, the time zone is determined based on
.Pa /etc/localtime ,
which the administrator adjusts using
the
.Fl l
option of
.Xr zic 8 .
.El
.Sh FILES
.Bl -tag -width /var/log/messages -compact
.It Pa /var/log/wtmp
record of date resets and time changes
.It Pa /var/log/messages
record of the user setting the time
.El
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
Display the date using the specified format string:
.Bd -literal -offset indent
$ date "+DATE: %Y-%m-%d%nTIME: %H:%M:%S"
DATE: 1987-11-21
TIME: 13:36:16
.Ed
.Pp
Set the date to
June 13, 1985, 4:27 PM:
.Pp
.Dl # date 198506131627
.Pp
Set the time to
2:32 PM,
without modifying the date:
.Pp
.Dl # date 1432
.Pp
If the mailing list server located in California
is being taken offline at 5:45 AM,
work out what time it will be locally, here in Tokyo:
.Pp
.Dl $ TZ=America/Los_Angeles date -j -z Asia/Tokyo 0545
.Sh SEE ALSO
.Xr adjtime 2 ,
.Xr gettimeofday 2 ,
.Xr strftime 3 ,
.Xr utmp 5 ,
.Xr ntpd 8 ,
.Xr rdate 8
.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2008
specification.
.Pp
The flags
.Op Fl afjrz ,
as well as the conversion specifiers
.Ql \&%F ,
.Ql \&%G ,
.Ql \&%g ,
.Ql \&%k ,
.Ql \&%l ,
.Ql \&%R ,
.Ql \&%s ,
.Ql \&%v ,
and
.Ql \&%+ ,
are extensions to that specification.
.Pp
This implementation requires the traditional
.Bx
date format,
[[[[[cc]yy]mm]dd]HH]MM[.SS],
which differs from the
X/Open System Interfaces option of the
.St -p1003.1-2008
specification.
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .