AT(C) XENIX System V AT(C)
Name
at, batch - Executes commands at a later time.
Syntax
at time [ date ] [ + increment ]
at-r job ...
at -l[ job ... ]
at -q[ letter ] time [ date ] [ job ... ]
Description
at and batch read commands from the standard input to be
executed at a later time. (batch has the same options shown
for at.) at allows you to specify a time when the commands
should be executed, while batch executes jobs when the
system load level permits.
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 priorities are lost.
A user is permitted to use at if their login name appears in
the file /usr/lib/cron/at.allow. If that file does not
exist, the file /usr/lib/cron/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 the at.deny file exists, global usage is permitted.
The allow/deny files consist of one user name per line.
The options are:
time The time may be specified as 1, 2, or 4 digits. One-
and two- digit numbers are taken to be hours, four
digits to be hours and minutes. The time may
alternately be specified as two numbers separated by a
colon, meaning hour:minute. A suffix am or pm may be
appended; otherwise a 24-hour clock time is understood.
The suffix zulu may be used to indicate GMT. The
special names noon, midnight, now, and next are also
recognized.
date An optional date may be specified as either a month
name followed by a day number (and possibly year number
preceded by an optional comma) or a day of the week
(fully spelled 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
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AT(C) XENIX System V AT(C)
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.
increment
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.) Thus, legitimate commands include:
at 0815am Jan 24
at 8:15am Jan 24
at now + 1 day
at 5 pm Friday
-r Removes jobs previously scheduled by the at or
batchcommand. Unless you are the super-user, you can
only remove your own jobs.
-l Lists all the jobs currently scheduled for the invoking
user.
-qletter
Places the specified job in a queue denoted by letter,
where letter is any letter from ``a'' to ``z'' (not
uppercase). The queue letter is appended to the job
number. The following letters have special
significance:
a at queue
b batch queue
c cron queue
at and batch write the job number and schedule time to
standard error. batch submits a batch job. It is almost
equivalent to ``at now,'' but with a difference: batch goes
into a different queue; at now will respond with the error
message ``too late.''
Examples
The at and batch commands read the commands to be executed
at a later time from the standard input. sh(C) provides
different ways of specifying standard input. Within your
commands, it may be useful to redirect standard output.
The following sequence can be used at a terminal:
batch
nroff filename > outfile
<Ctrl-D> (press ``Ctrl'' and press ``D'')
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This sequence, which demonstrates redirecting standard error
to a pipe ( | ), is useful in a shell procedure (the
sequence of output redirection specifications is
significant):
batch <<!
nroff 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 most simple use of at is to specify that a given command
or regular file containing commands, file, be run on the
date specified:
at date < file
Files
/usr/lib/cron main cron directory
/usr/lib/cron/at.allow list of allowed users
/usr/lib/cron/at.deny list of denied users
/usr/lib/cron/queue scheduling information
/usr/spool/cron/atjobs spool area
See Also
cron(C), kill(C), mail(C), nice(C), ps(C), sh(C)
Diagnostics
Complains about syntax errors and times out of range.
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