at(1) (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
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late; use now with the increment argument, such as: at now + 1
minute.
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.
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This sequence can be used at a terminal:
batch
sort filename > outfile
<control-D> (hold down `control' and depress `d')
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), in the System Administrator's Reference Manual.
environ(5), getdate(3C) in the Programmer's Reference Manual.
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DIAGNOSTICS
Complains about various syntax errors and times out of range.
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