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       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 implementation-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 separated  by  <space>  characters  and
                 concatenated, and shall be parsed as described in the grammar at the end of this
                 section. 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 digits.  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  category) 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

                           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 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), 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 day.

                           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 following 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 acceptable to the shell
       command language described in Chapter 2, Shell Command 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 implementation-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 variables that are unset or
                 null.  (See  the  Base  Definitions  volume  of   POSIX.1‐2008,   Section   8.2,
                 Internationalization   Variables  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 files).

                 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 of LC_MESSAGES.

       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  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 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 written 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 command 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  different  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 descriptors, traps, and priority inherited from
       the invoking environment are lost.

       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 redirection 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

               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

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

       Early  proposals  added a ``jobname'' concept as a way of giving submitted 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 functionality  is
       useful  in  simple  environments,  but  in  large or complex situations, the functionality
       provided by the Batch Services option is more suitable.

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

       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  appropriate  privileges  to
       access  the  work  of other users. Since this is primarily 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—does:

           at 1200 friday

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

       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 timezones 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 example:

           TZ= at noon ...

       gives the desired BSD result.

       While the yacc-like grammar specified in the OPERANDS  section  is  lexically  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  Electrical  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 .