PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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.

NAME         top

       at — execute commands at a later time

SYNOPSIS         top

       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...]

DESCRIPTION         top

       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.

OPTIONS         top

       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.

OPERANDS         top

       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 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
                                     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
             category.
           */

           %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"
                       ;

STDIN         top

       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.

INPUT FILES         top

       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.

ENVIRONMENT VARIABLES         top

       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).

       LC_MESSAGES
                 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.

ASYNCHRONOUS EVENTS         top

       Default.

STDOUT         top

       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).

STDERR         top

       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.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       The following exit values shall be returned:

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

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

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

       The following sections are informative.

APPLICATION USAGE         top

       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
           EOT
           job ... at ...
           $

EXAMPLES         top

        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
               !

        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
                   utc+
                   30minutes'

RATIONALE         top

       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
       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 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
       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.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       batch(1p), crontab(1p)

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

COPYRIGHT         top

       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 http://www.unix.org/online.html .

       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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                              AT(1P)

Pages that refer to this page: batch(1p)crontab(1p)