xref: /netbsd-src/bin/date/date.1 (revision 5a5d821f81fc28cf006b39df4ccd4123e2afd82b)

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.\"     @(#)date.1	8.3 (Berkeley) 4/28/95
.\"
.Dd September 17, 2024
.Dt DATE 1
.Os
.Sh NAME
.Nm date
.Nd display or set date and time
.Sh SYNOPSIS
.Nm
.Op Fl ajnRUu
.Op Fl d Ar date
.Op Fl r Ar seconds
.Op Fl z Ar 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 Cm \&. Ar SS
.Oc
.Sm on
.Nm
.Op Fl ajnRu
.Fl f Ar input_format
.Ar new_date
.Op Cm + Ns Ar format
.Sh DESCRIPTION
.Nm
displays the current date and time when invoked without arguments.
Providing arguments will format the date and time in a user-defined
way or set the date.
Only the superuser may set the date.
.Pp
The options are as follows:
.Bl -tag -width Fl
.It Fl a
Use
.Xr adjtime 2
to change the local system time slowly,
maintaining it as a monotonically increasing function.
.Fl a
implies
.Fl n .
.It Fl d Ar date
Parse the provided human-described date and time and display the result without
actually changing the system clock.
(See
.Xr parsedate 3
for examples.)
.It Fl f Ar input_fmt
Use
.Ar input_fmt
as the format string to parse the
.Ar new_date
provided rather than using the default
.Sm off
.Oo Oo Oo Oo Oo
.Ar CC Oc
.Ar yy Oc
.Ar mm Oc
.Ar dd Oc
.Ar HH Oc
.Ar MM
.Op Cm \&. Ar SS
.Sm on
format.
Parsing is done using
.Xr strptime 3 .
.It Fl j
Parse the provided canonical representation of date and time (described below)
and display the result without actually changing the system clock.
.It Fl n
The utility
.Xr timed 8
is used to synchronize the clocks on groups of machines.
By default, if
.Xr timed 8
is running,
.Nm
will set the time on all of the machines in the local group.
The
.Fl n
option stops
.Nm
from setting the time for other than the current machine.
.It Fl R
Use a default display format that conforms to the date and time
specification in RFC 5322 (Internet Message Format).
.It Fl r Ar seconds
Print out the date and time that is
.Ar seconds
from the Epoch.
.It Fl U
Reset the timezone used by
.Nm
to that which existed when it was invoked.
This is only useful after an earlier
.Fl u
or
.Fl z
option.
.It Fl u
Display or set the date in UTC (universal) time.
.It Fl z Ar zone
Set the timezone to be used by
.Nm
to
.Ar zone .
If
.Ar zone
is an empty string, revert to the system's
default timezone (ignoring any setting of
.Ev TZ ) .
.El
.Pp
Note the
.Fl d ,
.Fl U ,
.Fl u ,
and
.Fl z
options are applied when encountered, hence specifying
.Fl u
before
.Fl d
will cause the
.Ar date
to be parsed as coordinated universal time, by default,
whereas if
.Fl u
is specified after
.Fl d
the
.Ar date
will be parsed using the default timezone, then
output will be generated in UTC.
.Pp
An operand with a leading plus
.Pq Cm +
sign 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
.Aq newline
character is always output after the characters
specified by the format string.
The format string for the default display is:
.Pp
.Dl %a %b %e %H:%M:%S %Z %Y
.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 CC
The first two digits of the year (the century).
.It Ar yy
The second two digits of the year.
If
.Ar yy
is specified, but
.Ar CC
is not, a value for
.Ar yy
between 69 and 99 results in a
.Ar CC
value of 19.
Otherwise, a
.Ar CC
value of 20 is used.
.It Ar mm
The month of the year, from 01 to 12.
.It Ar dd
The day of the month, from 01 to 31.
.It Ar HH
The hour of the day, from 00 to 23.
.It Ar MM
The minute of the hour, from 00 to 59.
.It Ar SS
The second of the minute, from 00 to 60.
.El
.Pp
Everything but the minutes is optional.
.Pp
Time changes for Daylight Saving and Standard Time and leap seconds
and years are handled automatically.
.Sh ENVIRONMENT
The following environment variables affect the execution of
.Nm :
.Bl -tag -width Ev
.It Ev TZ
The timezone to use when displaying dates.
See
.Xr environ 7
for more information.
.El
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /etc/localtime
Symlink pointing to system's default timezone information file in
.Pa /usr/share/zoneinfo
directory.
.It Pa /usr/lib/locale/ Ns Ao Ar L Ac Ns Pa /LC_TIME
Description of time locale
.Aq Ar L .
.It Pa /usr/share/zoneinfo
Time zone information directory.
.It Pa /usr/share/zoneinfo/posixrules
Used with POSIX-style TZ's.
.It Pa /usr/share/zoneinfo/GMT
For UTC leap seconds.
.It Pa /var/log/wtmp
A record of date resets and time changes.
.It Pa /var/log/messages
A record of the user setting the time.
.El
.Pp
If
.Pa /usr/share/zoneinfo/GMT
is absent, UTC leap seconds are loaded from
.Pa /usr/share/zoneinfo/posixrules .
.Sh EXAMPLES
The command:
.Pp
.Dl date '+DATE: %m/%d/%y%nTIME: %H:%M:%S'
.Pp
will display:
.Bd -literal -offset indent
DATE: 11/21/87
TIME: 13:36:16
.Ed
.Pp
The command:
.Pp
.Dl date 8506131627
.Pp
sets the date to
.Dq Li "June 13, 1985, 4:27 PM" .
.Pp
The command:
.Pp
.Dl date 1432
.Pp
sets the time to
.Li "2:32 PM" ,
without modifying the date.
.Pp
The command:
.Pp
.Dl date +%s
.Pp
prints the current time as seconds since the Epoch.
.Pp
The command:
.Pp
.Dl date -z America/Chicago -d 13:00 -z Asia/Tokyo +%H:%M
.Pp
indicates what the time will be in Tokyo when it is 13:00
in Chicago.
Any
.Xr strftime 3
string could be used for the output.
The first
.Fl z
option can be omitted to parse the time as specified by
.Ev TZ
.Pq usually the local timezone ,
or the second could be replaced by
.Fl U
to show the parsed time in the local timezone.
.Pp
Either of the commands:
.Pp
.Dl date -u -d 1970-01-01T00:00:00 -U +%c
.Dl date -r 0 +%c
.Pp
print the local time of the
.Ux
epoch.
.Sh DIAGNOSTICS
Exit status is 0 on success, 1 if unable to set the date, and 2
if able to set the local date, but unable to set it globally.
.Pp
Occasionally, when
.Xr timed 8
synchronizes the time on many hosts, the setting of a new time value may
require more than a few seconds.
On these occasions,
.Nm
prints:
.Ql Network time being set .
The message
.Ql Communication error with
.Xr timed 8
occurs when the communication
between
.Nm
and
.Xr timed 8
fails.
.Sh SEE ALSO
.Xr adjtime 2 ,
.Xr gettimeofday 2 ,
.Xr settimeofday 2 ,
.Xr parsedate 3 ,
.Xr strftime 3 ,
.Xr utmp 5 ,
.Xr environ 7 ,
.Xr timed 8
.Rs
.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
.%A R. Gusella
.%A S. Zatti
.Re
.Sh STANDARDS
The
.Nm
utility is expected to be compatible with
.St -p1003.2 .
However, achieving true compatability requires running
.Nm
with the environment variable
.Ev POSIXLY_CORRECT
set, in order to parse the time string in the
archaic format POSIX demands, rather than the
more rational version described above.
.Sh HISTORY
A
.Nm
utility appeared in
.At v1 .