at(1p) — Linux manual page


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

OPTIONS         top

       The at utility shall conform to the Base Definitions volume of
       POSIX.1‐2017, 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

       -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

       -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

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

                           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"

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.


       The following environment variables shall affect the execution of

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base
                 Definitions volume of POSIX.1‐2017, 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

       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.



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




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.


       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 ...

EXAMPLES         top

        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 include:

               at 0815am Jan 24
               at 8 :15amjan24
               at now "+ 1day"
               at 5 pm FRIday
               at '17

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

       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.



SEE ALSO         top

       batch(1p), crontab(1p)

       The Base Definitions volume of POSIX.1‐2017, 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 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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 .

IEEE/The Open Group               2017                            AT(1P)

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