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AT(1P)			   POSIX Programmer's Manual			AT(1P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       at — execute commands at a later time

       at [−m] [−f file] [−q queuename] −t time_arg

       at [−m] [−f file] [−q queuename] timespec...

       at −r at_job_id...

       at −l −q queuename

       at −l [at_job_id...]

       The at utility shall read commands from standard input and  group  them
       together as an at-job, to be executed at a later time.

       The  at-job  shall  be  executed in a separate invocation of the shell,
       running in a separate  process  group  with  no	controlling  terminal,
       except  that the environment variables, current working directory, file
       creation	 mask,	 and   other   implementation-defined	execution-time
       attributes  in effect when the at utility is executed shall be retained
       and used when the at-job is executed.

       When the at-job is submitted, the at_job_id and scheduled time shall be
       written to standard error. The at_job_id is an identifier that shall be
       a string consisting solely of alphanumeric characters and the  <period>
       character.  The	at_job_id shall be 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.

       Users  shall  be	 permitted to use at if their name appears in the file
       at.allow which is located in an implementation-defined  directory.   If
       that  file  does	 not  exist,  the file at.deny, which is located in an
       implementation-defined directory, shall be checked to determine whether
       the  user shall be denied access to at.	If neither file exists, only a
       process with appropriate privileges shall be allowed to submit  a  job.
       If  only	 at.deny exists and is empty, global usage shall be permitted.
       The at.allow and at.deny files shall consist of one user name per line.

       The at  utility	shall  conform	to  the	 Base  Definitions  volume  of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       −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 for  these  jobs.  The
		 output shall 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 shall be mailed to the user as well,
		 unless redirected elsewhere. Mail shall be sent even  if  the
		 job produces no output.

		 If  −m	 is  not  used, the job's standard output and standard
		 error shall be provided to the user by means of mail,	unless
		 they  are redirected elsewhere; if there is no such output to
		 provide, the implementation need 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 shall be scheduled in queue a.  In
		 contrast, queue b shall  be  reserved	for  batch  jobs;  see
		 batch.	  The meanings of all other queuenames are implementa‐
		 tion-defined. If −q is specified along with either of the  −t
		 time_arg or timespec arguments, the results are unspecified.

       −r	 Remove	 the  jobs  with the specified at_job_id operands that
		 were previously scheduled by the at utility.

       −t time_arg
		 Submit the job to be run at the time specified	 by  the  time
		 option-argument,  which  the application shall ensure has the
		 format as specified by the touch −t time utility.

       The following operands shall be 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 sep‐
		 arated	 by  <space> characters and concatenated, and shall be
		 parsed as described in the grammar at the end	of  this  sec‐
		 tion.	The date and time shall be interpreted as being in 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 shall be recognized in
		 a case-insensitive manner.

		 time	   The time can be specified as one, two, or four dig‐
			   its. One-digit and two-digit numbers shall be 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 cate‐
			   gory)  can  follow  the  time; otherwise, a 24-hour
			   clock time shall be understood. A timezone name can
			   also	 follow	 to  further  qualify  the  time.  The
			   acceptable  timezone	 names	 are   implementation-
			   defined, except that they shall be case-insensitive
			   and the string utc is  supported  to	 indicate  the
			   time	 is  in	 Coordinated  Universal	 Time.	In the
			   POSIX locale, the time field can also be one of the
			   following tokens:

			   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> shall submit an	at-job
				     for potentially immediate execution (that
				     is, subject only to unspecified  schedul‐
				     ing delays).

		 date	   An optional date can be specified as either a month
			   name (one of the values from the mon or abmon  key‐
			   words in the LC_TIME locale category) followed by a
			   day number (and possibly year number preceded by  a
			   comma),  or	a  day	of the week (one of the values
			   from the day	 or  abday  keywords  in  the  LC_TIME
			   locale  category). In the POSIX locale, two special
			   days shall be recognized:

			   today     Indicates the current day.

			   tomorrow  Indicates the day following  the  current

			   If  no date is given, today shall be assumed if the
			   given time is greater than the  current  time,  and
			   tomorrow  shall  be	assumed	 if it is less. If the
			   given month is less than the current month (and  no
			   year is given), next year shall be assumed.

		 increment The	optional  increment shall be a number preceded
			   by a <plus-sign> ('+') and suffixed by one  of  the
			   following:  minutes, hours, days, weeks, months, or
			   years.   (The  singular   forms   shall   also   be
			   accepted.)  The keyword next shall be equivalent to
			   an increment number of +1. For example, the follow‐
			   ing are equivalent commands:

			       at 2pm + 1 week
			       at 2pm next week

       The  following  grammar describes the precise format of timespec in the
       POSIX locale. The general conventions for this  style  of  grammar  are
       described  in  Section  1.3,  Grammar  Conventions.  This formal syntax
       shall take precedence over the preceding text syntax  description.  The
       longest	possible  token	 or  delimiter	shall be recognized at a given
       point. When used in a timespec, white space shall also delimit tokens.

	   %token hr24clock_hr_min
	   %token hr24clock_hour
	     An hr24clock_hr_min is a one, two, or four-digit number. A one-digit
	     or two-digit number constitutes an hr24clock_hour. An hr24clock_hour
	     may be any of the single digits [0,9], or may be double digits, ranging
	     from [00,23]. If an hr24clock_hr_min is a four-digit number, the
	     first two digits shall be a 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-digit, or four-digit number.
	     A one-digit 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 shall be a valid
	     wallclock_hour, while the last two represent the number of
	     minutes, from [00,59].

	   %token minute
	     A minute is a one or two-digit number whose value 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-defined 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

	   %start timespec
	   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"

       The standard input shall be a text file consisting of commands  accept‐
       able  to	 the shell command language described in Chapter 2, Shell Com‐
       mand Language.  The standard input shall only be used  if  no  −f  file
       option is specified.

       See the STDIN section.

       The  text files at.allow and at.deny, which are located in an implemen‐
       tation-defined directory, shall contain zero or more  user  names,  one
       per  line,  of users who are, respectively, authorized or denied access
       to the at and batch utilities.

       The following environment variables shall affect the execution of at:

       LANG	 Provide a default value for  the  internationalization	 vari‐
		 ables	that are unset or null. (See the Base Definitions vol‐
		 ume of POSIX.1‐2008, Section 8.2, Internationalization	 Vari‐
		 ables	for  the  precedence of internationalization variables
		 used to determine the values of locale categories.)

       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-byte as
		 opposed  to  multi-byte  characters  in  arguments  and input

		 Determine the locale that should be used to affect the format
		 and contents of diagnostic messages written to standard error
		 and informative messages written to standard output.

       NLSPATH	 Determine the location of message catalogs for the processing

       LC_TIME	 Determine  the	 format and contents for date and time strings
		 written and accepted 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 shall
		 be used. If it is set to a value other than a	name  for  sh,
		 the  implementation  shall  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 timezone. The job shall be submitted for execu‐
		 tion at the time specified by timespec or −t time relative to
		 the timezone specified by the TZ variable. If timespec speci‐
		 fies  a timezone, it shall override TZ.  If timespec does not
		 specify a timezone and TZ is unset or	null,  an  unspecified
		 default timezone shall be used.


       When  standard  input  is a terminal, prompts of unspecified format for
       each line of the user input described in the STDIN section may be writ‐
       ten to standard output.

       In  the	POSIX  locale,	the following shall 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 shall be equivalent in format to the output of:

	   date +"%a %b %e %T %Y"

       The date and time written shall be adjusted so that they appear in  the
       timezone of the user (as determined by the TZ variable).

       In  the	POSIX locale, the following shall 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 that described in the STDOUT section.
       Neither this, nor warning messages concerning the selection of the com‐
       mand interpreter, shall be considered a	diagnostic  that  changes  the
       exit status.

       Diagnostic messages, if any, shall be written to standard error.



       The following exit values shall be returned:

	0    The  at  utility successfully submitted, removed, or listed a job
	     or jobs.

       >0    An error occurred.

       The job shall not be scheduled, removed, or listed.

       The following sections are informative.

       The format of the at command line shown here is guaranteed only for the
       POSIX  locale.  Other cultures may be supported with substantially dif‐
       ferent interfaces, although implementations are encouraged  to  provide
       comparable levels of functionality.

       Since  the  commands  run  in a separate shell invocation, running in a
       separate process group with no controlling terminal, open file descrip‐
       tors,  traps,  and priority inherited from the invoking environment are

       Some implementations do not  allow  substitution	 of  different	shells
       using  SHELL.  System V systems, for example, have used the login shell
       value for the user in /etc/passwd.  To select reliably another  command
       interpreter, the user must include it as part of the script, such as:

	   $ at 1800
	   myshell myscript
	   job ... at ...

	1. This sequence can be used at a terminal:

	       at −m 0730 tomorrow
	       sort < file >outfile

	2. This	 sequence,  which demonstrates redirecting standard error to a
	   pipe, is useful in a command procedure (the sequence of output  re‐
	   direction specifications is significant):

	       at now + 1 hour <<!
	       diff file1 file2 2>&1 >outfile | mailx mygroup

	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
	   runs	 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 "+ 1day"
	       at 5 pm FRIday
	       at '17

       The at utility reads from standard input the commands to be executed at
       a later time. It may be useful to redirect standard output and standard
       error within the specified commands.

       The −t time option was added as a new capability to support an interna‐
       tionalized way of specifying a time for execution of the submitted job.

       Early  proposals added a ``jobname'' concept as a way of giving submit‐
       ted jobs names that are meaningful to the user  submitting  them.   The
       historical,  system-specified at_job_id gives no indication of what the
       job is. Upon further reflection, it was decided	that  the  benefit  of
       this was not worth the change in historical interface. The at function‐
       ality is useful in simple environments, but in large or complex	situa‐
       tions,  the functionality provided by the Batch Services option is more

       The −q option historically has been an undocumented option, used mainly
       by the batch utility.

       The  System  V  −m  option  was added to provide a method for informing
       users that an at-job had completed. Otherwise, users are only  informed
       when output to standard error or standard output are not redirected.

       The  behavior  of  at <now> was changed in an early proposal from being
       unspecified to submitting a job for  potentially	 immediate  execution.
       Historical  BSD	at  implementations  support this. Historical System V
       implementations give an error in that case, but a change to the	System
       V versions should have no backwards-compatibility ramifications.

       On BSD-based systems, a −u user option has allowed those with appropri‐
       ate privileges to access the work of other users. Since this is primar‐
       ily a system administration feature and is not universally implemented,
       it has been omitted. Similarly, a specification for the	output	format
       for  a  user  with  appropriate	privileges viewing the queues of other
       users has been omitted.

       The −f file option from System V is used instead of the BSD  method  of
       using  the  last	 operand as the pathname. The BSD method is ambiguous—

	   at 1200 friday

       mean the same thing if there is a file  named  friday  in  the  current

       The  at_job_id  is  composed  of	 a limited character set in historical
       practice, and it is mandated here to invalidate systems that might  try
       using characters that require shell quoting or that could not be easily
       parsed by shell scripts.

       The at utility varies between System V and BSD systems in the way time‐
       zones are used. On System V systems, the TZ variable affects the at-job
       submission times and the times displayed for the user. On BSD  systems,
       TZ  is not taken into account. The BSD behavior is easily achieved with
       the current specification. If the user  wishes  to  have	 the  timezone
       default to that of the system, they merely need to issue the at command
       immediately following an unsetting or null assignment to TZ.  For exam‐

	   TZ= at noon ...

       gives the desired BSD result.

       While  the yacc-like grammar specified in the OPERANDS section is lexi‐
       cally unambiguous with respect to the digit strings, a lexical analyzer
       would probably be written to look for and return digit strings in those
       cases. The parser could then check whether the digit string returned is
       a valid day_number, year_number, and so on, based on the context.


       batch, crontab

       The  Base  Definitions  volume  of POSIX.1‐2008, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained	online
       at .

       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker‐ .

IEEE/The Open Group		     2013				AT(1P)

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