at(1) UNIX System V(User Environment Utilities) at(1)
NAME
at, batch - execute commands at a later time
SYNOPSIS
at [-f script] [-m] time [date] [+ increment]
at -l [job ...]
at -r job ...
batch
DESCRIPTION
at and batch read commands from standard input to be executed at a later
time. at allows you to specify when the commands should be executed,
while jobs queued with batch will execute when system load level permits.
at may be used with the following options:
-f script Reads commands to be executed from the named script file.
-l [job] Reports all jobs scheduled for the invoking user, or just the
jobs specified.
-m Sends mail to the user after the job has been completed,
indicating that the job is finished, even if the job produces
no output. Mail is sent only if the job has not already
generated a mail message.
-r job Removes specified jobs previously scheduled using at.
Standard output and standard error output are mailed to the user unless
they are redirected elsewhere. The shell environment variables, current
directory, umask, and ulimit are retained when the commands are executed.
Open file descriptors, traps, and priority are lost.
Users are permitted to use at if their name appears in the file
/usr/sbin/cron.d/at.allow. If that file does not exist, the file
/usr/sbin/cron.d/at.deny is checked to determine if the user should be
denied access to at. If neither file exists, only root is allowed to
submit a job. If only at.deny exists and is empty, global usage is
permitted. The allow/deny files consist of one user name per line.
These files can only be modified by the privileged user.
If the DATEMSK environment variable is set, it points to a template file
that at will use to determine the valid time and date values instead of
the values described below. For more information about using DATEMSK,
see the last paragraph of the DESCRIPTION section.
time may be specified as follows, where h is hours and m is minutes: h,
hh, hhmm, h:m, h:mm, hh:m, hh:mm. A 24-hour clock is assumed, unless am
or pm is appended to time. If zulu is appended to time, it means
Greenwich Mean Time (GMT). time can also take on the values: noon,
midnight, and now. at now responds with the error message too late; use
now with the increment argument, such as: at now + 1 minute.
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An optional date may be specified as either a month name followed by a
day number (and possibly a year number preceded by a comma) or a day of
the week. (Both the month name and the day of the week may be spelled
out or abbreviated to three characters.) Two special ``days'', today and
tomorrow are recognized. If no date is given, today is assumed if the
given hour is greater than the current hour and tomorrow is assumed if it
is less. If the given month is less than the current month (and no year
is given), next year is assumed.
The optional increment is simply a number suffixed by one of the
following: minutes, hours, days, weeks, months, or years. (The singular
form is also accepted.) The modifier next may precede the increment; it
means ``+ 1.''
Thus valid commands include:
at 0815am Jan 24
at 8:15am Jan 24
at now + 1 day
at now next day
at 5 pm Friday
at and batch write the job number and schedule time to standard error.
at -r removes jobs previously scheduled by at or batch. The job number
is the number returned to you previously by the at or batch command. You
can also get job numbers by typing at -l. You can only remove your own
jobs unless you are the privileged user.
If the environment variable DATEMSK is set, at will use its value as the
full path name of a template file containing format strings. The strings
consist of field descriptors and text characters and are used to provide
a richer set of allowable date formats in different languages by
appropriate settings of the environment variable LANG or LCTIME (see
environ(5)). (See getdate(3C) for the allowable list of field
descriptors; this list is a subset of the descriptors allowed by
calendar(1) that are listed on the date(1) manual page.) The formats
described above for the time and date arguments, the special names noon,
midnight, now, next, today, tomorrow, and the increment argument are not
recognized when DATEMSK is set.
EXAMPLES
The at and batch commands read from standard input the commands to be
executed at a later time. sh(1) provides different ways of specifying
standard input. Within your commands, it may be useful to redirect
standard output.
This sequence can be used at a terminal:
batch
sort filename > outfile
<control-D> (hold down `control' and depress `d')
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This sequence, which shows redirecting standard error to a pipe, is
useful in a shell procedure (the sequence of output redirection
specifications is significant):
batch <<!
sort filename 2>&1 > outfile | mail loginid
!
To have a job reschedule itself, invoke at from within the shell
procedure, by including code similar to the following within the shell
file:
echo "sh shellfile" | at 1900 thursday next week
The following example shows the possible contents of a template file
AT.TEMPL in /var/tmp.
%I %p, the %est of %B of the year %Y run the following job
%I %p, the %end of %B of the year %Y run the following job
%I %p, the %erd of %B of the year %Y run the following job
%I %p, the %eth of %B of the year %Y run the following job
%d/%m/%y
%H:%M:%S
%I:%M%p
The following are examples of valid invocations if the environment
variable DATEMSK is set to /var/tmp/AT.TEMPL.
at 2 PM, the 3rd of July of the year 2000 run the following job
at 3/4/99
at 10:30:30
at 2:30PM
FILES
/usr/sbin/cron.d main cron directory
/usr/sbin/cron.d/at.allowlist of allowed users
/usr/sbin/cron.d/at.denylist of denied users
/usr/sbin/cron.d/queuedefsscheduling information
/var/spool/cron/atjobsspool area
SEE ALSO
atq(1), atrm(1), calendar(1), crontab(1), date(1), kill(1), mail(1),
nice(1), ps(1), sh(1), sort(1).
cron(1M), environ(5), in the System Administrator's Reference Manual.
getdate(3C) in the Programmer's Reference Manual.
DIAGNOSTICS
Complains about various syntax errors and times out of range.
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