at(1)at(1)NAME
at, batch - execute commands at a later time
SYNOPSIS
at [-m] [-f file] [-q queuename] -t time
at [-m] [-f file] [-q queuename] timespec
at -r at_job_id ...
at -l -q queuename
at -l [at_job_id ...]
batchDESCRIPTION
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.
The at utility reads commands from standard input and groups them
together as an at-job, to be executed at a later time.
The at-job will be executed in a separate invocation of the shell,
running in a separate process group with no controlling terminal, except
that of the environment variables, current working directory, file
creation mask, and other implementation-dependent execution-line
attributes in effect when the at utility is executed wil be retained and
used when the at-job is executed. The shell umask and ulimit are
retained when the commands are executed. Open file descriptors, traps,
and priority are lost.
When the at-job is submitted, the at_job_id and scheduled time are
written to standard error. The at_job_id is an identifier that will be a
string consisting solely of alphanumeric characters and the period
character. The at_job_id is assigned by the system when the job is
scheduled such that it uniquely identifies a particular job.
User notification and the processing of the job's standard output and
standard error are described under the -m option.
If the file /usr/lib/cron/at.allow. exists, only users whose names appear
in the file are permitted to use at. This restriction applies to all
users, including root. 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 a process with the
appropriate privileges is allowed to submit a job. If only at.deny exists
and is empty, global usage is permitted. The at.allow and at.deny files
consist of one user name per line. These files can only be modified by
the superuser.
OPTIONS
The at utility supports the XBD specification, Section 10.2, Utility
Syntax Guidelines.
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at may be used with the following options:
-f file
Specify the pathname of a file to be used as the source of the at-
job, instead of standard input.
-l (The letter ell.) Report all jobs scheduled for the invoking user if
no at_job_id operands are specified. If at_job_ids are specified,
report only information on these jobs. The output will be written to
standard output.
-m Send mail to the invoking user after the at-job has run, announcing
its completion. Standard output and standard error produced by the
at-job will be mailed to the user as well, unless directed
elsewhere. Mail will be sent even if the job produces no output.
If -m is not used, the job's standard output and standard error will
be provided to the user by means of mail, unless they are redirected
elsewhere; if there is no such output to provide, the implementation
needs not notify the user of the job's completion.
-q queuename
Specify in which queue to schedule a job for submission. When used
with the -l option, limit the search to that particular queue. By
default, at-jobs will be scheduled in queue a. In contrast, queue b
is reserved for batch jobs. (see the batch utility.) The meanings
of all other queuenames are implementation-dependent.
-r Remove the jobs with the specified at_job_ids that were previously
scheduled with at. You can only remove your own jobs unless you are
the superuser.
-t time
Submit the job to be run at the time specified by the time option
argument, which must have the format as specified by the touch
utility.
All jobs are placed on a specific queue. By default, at jobs go on queue
``a'', batch jobs go on queue ``b''. Additional queues may be created by
altering the /usr/lib/cron/queuedefs file. queuedefs(4) defines the
format for that file. Note that queue names must be lower case letters.
OPERANDS
The following operands are supported:
at_job_id
The name reported by a previous invocation of the at utility at the
time the job was scheduled.
timespec
Submit the job to be run at the date and time specified. All of the
timespec operands are interpreted as if they were separated by space
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characters and concatenated, and are parsed as described in the
grammar at the end of this section. The date and time are
interpreted as being the timezone of the user (as determined by the
TZ variable), unless a timezone name appears as part of time below.
In the POSIX locale, the following describes the three parts of the
time specification string. All of the values from the LC_TIME
categories in the POSIX locale are recognized in a case-insensitive
manner.
time The time can be specified as one, two, or four digits. One- and
two-digit numbers are taken to be hours, four-digit numbers to
be hours and minutes. The time can alternatively be specified
as two numbers separated by a colon, meaning hour:minute. An
AM/PM indication (one of the values from the am_pm keywords in
the LC_TIME locale category) can follow the time; otherwise, a
24-hour clock time is understood. A timezone name can also
follow to further qualify the time. The acceptable timezone
names are implementation-dependent, except that they will be
case-insensitive and the string utc is supported to indicate
the time in Coordinated Universal Time. The suffix zulu may be
used to indicate GMT.
The time field can also be one of the following tokens in the
POSIX locale:
midnight
Indicates the time 12:00 am (00:00).
noon Indicates the time 12:00 pm.
now Indicates the current day and time. Invoking at now will
submit an at-job for potentially immediate execution (that
is, subject only to unspecified scheduling delays).
date An optional date can be specified as either a month name (one
of the values from the mon or abmon keywords in the LC_TIME
locale category) followed by a day number (and possibly year
number preceded by a comma, two digit years 00-37 and 70-99
represent 2000-2037 and 1970-1999 respectively, all years
inclusive) or a day of the week (one of the values from the day
or abday keywords in the LC_TIME locale category). Two special
days are recognized in the POSIX locale:
today
Indicates the current day.
tomorrow
Indicates the day following the current day.
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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.
increment
The optional increment is simply a number preceded by a plus
sign (+) and suffixed by one of the following: minutes, hours,
days, weeks, months, or years. (The singular form is also
accepted.) The keyword next is equivalent to an increment
number of +1. For example, the following are equivalent
command:
at 2pm + 1 week
at 2pm next week
Thus legitimate commands include:
at 0815am Jan 24
at 8:15am Jan 24
at now + 1 day
at 5 pm Friday
The following grammar describes the precise format of timespec in the
POSIX locale. This formal syntax takes precedence over the preceding text
syntax description. When used in a timespec, white space also delimits
tokens.
%token hr24clock_hr_min
%token hr24clock_hour
/*
A hr24clock_hr_min is a one, two or four digit number. A one or two digit
number constitutes a hr24clock_hour. A hr24clock_hour may be any of the
single digits '0' - '9', or may be double digits, ranging from "00" -
"23". If a hr24clock_hr_min is a four digit number, the first two digits
must be valid hr24clock_hour, while the last two represent the number of
minutes, from "00" - "59".
*/
%token wallclock_hr_min
%token wallclock_hour
/*
A wallclock_hr_min is a one, two or four digit number. A one or two digit
number constitutes a wallclock_hour. A wallclock_hour may be any of the
single digits '1' - '9', or may be double digits, ranging from "01" -
"12". If a wallclock_hr_min is a four digit number, the first two digits
must be valid wallclock_hour, while the last two represent the number of
minutes, from "00" - "59".
*/
%token minute
/*
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A minute is a one or two digit number whose values can be '0' - '9' or
"00" - "59".
*/
%token day_number
/*
A day_number is a number in the range appropriate for the particular
month and year specified by month_name and year_number, respectively. If
no year_number is given, the current year is assumed if the given date
and time are later this year. If no year_number is given and the date and
time have already occurred this year and the month is not the current
month, next year is the assumed year.
*/
%token year_number
/*
A year_number is a four digit number representing the year A.D., in which
the at_job is to be run
*/
%token inc_number
/*
The inc_number is the number of times the succeeding increment period is
to be added to the specified date and time.
*/
%token timezone_name
/*
The name of an optional timezone suffix to the time field, in an
implementation dependent format.
*/
%token month_name
/*
One of the values from the "mon" or "abmon" keywords in the LC_TIME
locale category.
*/
%token day_of_week
/*
One of the values from the "day" or "abday" keywords in the LC_TIME
locale category.
*/
%token am_pm
/*
One of the values from the "am_pm" keyword in the LC_TIME locale
category.
*/
%start timespec
%%
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timespec : time
| time date
| time increment
| time date increment
| nowspec
;
nowspec : "now"
| "now" increment
;
time : hr24clock_hr_min
| hr24clock_hr_min timezone_name
| hr24clock_hour ":" minute
| hr24clock_hour ":" minute timezone_name
| wallclock_hr_min am_pm
| wallclock_hr_min am_pm timezone_name
| wallclock_hour ":" minute am_pm
| wallclock_hour ":" minute am_pm timezone_name
| "noon"
| "midnight"
;
date : month_name day_number
| month_name day_number "," year_number
| day_of_week
| "today"
| "tomorrow"
;
increment : "+" inc_number inc_period
| "next" inc_period
;
inc_period : "minute" | "minutes"
| "hour" | "hours"
| "day" | "days"
| "week" | "weeks"
| "month" | "months"
| "year" | "years"
;
batch submits a batch job. It is almost equivalent to at now, but not
quite. For one, it goes into a different queue.
STDIN
The standard input must be a text file consisting of commands acceptable
to the shell command language. The standard input will only be used if no
-f file option is specified.
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at(1)at(1)ENVIRONMENT VARIABLES
The following environment variables affect the execution of at:
LANG provide a default value for the internationalization variables that
are unset or null. If LANG is unset or null the corresponding value
from the implementation-specific default locale will be used. If any
of the internationalization variables contains an invalid setting,
the utility will behave as if none of the variables had been
defined.
LC_ALL
if set to a non-empty string value, override the values of all the
other internationalization variables.
LC_CTYPE
determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single - as opposed to multi-
byte - characters in arguments).
LC_MESSAGES
determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
NLSPATH
determine the location of message catalogs for the processing of
LC_MESSAGES.
LC_TIME
determine the format and contents of date and time strings written
by at
SHELL
determine a name of a command interpreter to be used to invoke the
at-job. If the variable is unset or null, sh will be used. If it is
set to a value other than a name for sh, the implementation will do
one of the following: use that shell; use sh; use the login shell
from the user database; or any of the preceding accompanied by a
warning diagnostic about which was chosen.
TZ determine the time zone. The job will be subnmitted for execution at
the time specified by timespec or -t time relative to the timezone
specified by the TZ variable. If timespec specifies a timezone, it
will override TZ. If timespec does not specify a timezone and TZ is
unset or null, an unspecified default timezone will be used.
STDOUT
When standard input is a terminal, prompts of unspecified format for each
line of the user input described in STDIN may be written to standard
output.
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In the POSIX locale, the following will be written to the standard output
for each job when jobs are listed in response to the -l option:
"%s\t%s\n", at_job_id, <date>
where <date> is equivalent in format to the output of:
date +"%a %b %e %T %Y"
The date and time written will be adjusted so that they appear in the
timezone of the user (as determined by the TZ variable).
STDERR
The following will be written to standard error when a job has been
successfully submitted:
"job %s at %s\n", at_job_id, <date>
where <date> has the same format as is described in STDOUT interpreter,
are considered a diagnostic that changes the exit status.
Diagnostic messages, if any, are written to standard error.
EXIT STATUS
The following exit values are returned:
0 successful completion
>0 an error occurred
CONSEQUENCES OF ERRORS
The job will not be scheduled, removed or listed.
EXAMPLES
The at and batch commands read from standard input the commands to be
executed at a later time.
1. This sequence can be used at a terminal:
at -m 0730 tomorrow
sort <file >outfile
EOT
2. This sequence, which demonstrates redirecting standard error to a
pipe, is useful in a command procedure (the sequence of output
redirection specifications is significant):
at now + 1 hour <<!
diff file1 file2 2>&1 >outfile | mailx mygroup
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3. To have a job reschedule itself, at can be invoked from within the
at-job. For example, this daily processing script named my.daily will run
every day (although crontab is a more appropriate vehicle for such work):
#my.daily runs every day
daily processing
at now tomorrow < my.daily
4. The spacing of the three portions of the POSIX locale timespec is
quite flexible as long as there are no ambiguities. Examples of various
times and operand presentation include:
at 0815am Jan 24
at 8 :15amjan24
at now "+ 1 day"
at 5 pm FRIday
sh(1) provides different ways of specifying standard input. Within your
commands, it may be useful to redirect standard output.
5. This sequence can be used at a terminal:
batch
sort filename >outfile
<control-D> (hold down 'control' and depress 'D')
6. 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 <<!
sort filename 2>&1 >outfile | mail loginid
!
7. 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
or, from a terminal
at 1900 thursday next week
sh shellfile
<control-D> (hold down 'control' and depress 'D')
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/spool/cron/atjobs spool area
/usr/lib/cron/.proto generic prototype, prepended to all jobs
/usr/lib/cron/.proto.x prototype for queue `x'
/usr/lib/cron/queuedefs definitions for queues
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at(1)at(1)SEE ALSOcron(1M), kill(1), mail(1), nice(1), ps(1), sh(1), sort(1), proto(4),
queuedefs(4).
DIAGNOSTICS
Complains about various syntax errors and times out of range.
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