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       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
       /usr/lib/cron/at.allow.  If that file does not exist, the file /usr/lib/cron/at.deny shall
       be checked to determine whether the user shall be denied access to  at.  If  neither  file
       exists,  only  a process with the 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 IEEE Std 1003.1-2001,
       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


       The following operands shall be supported:

              The name reported by a previous invocation of the at utility at the  time  the  job
              was scheduled.

              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>s  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,

       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.

              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 tokens:

                     Indicates the time 12:00 am (00:00).

                     Indicates the time 12:00 pm.

                     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).

              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:

                     Indicates the current day.

                     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.

              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 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 Shell Command Language . The standard input shall only be
       used if no -f file option is specified.


       See the STDIN section.

       The text files /usr/lib/cron/at.allow and /usr/lib/cron/at.deny 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  IEEE Std 1003.1-2001, 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.

              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.

              Determine the location of message catalogs for the processing of LC_MESSAGES .

              Determine the format and contents for date and time strings written and accepted by

       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 processingat 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


       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. 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 .