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...]
- −f file
- Specify the pathname of a file to be used as the source of the at-job, instead of standard input.
- (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.
- 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
- 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 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> 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.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.
- 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.
- 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
%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" ;
- 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.)
- 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 location of message catalogs for the processing of LC_MESSAGES.
- Determine the format and contents for date and time strings written and accepted by at.
- 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.
- 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.
"%s\t%s\n", at_job_id, <date>
date +"%a %b %e %T %Y"
"job %s at %s\n", at_job_id, <date>
- The at utility successfully submitted, removed, or listed a job or jobs.
- An error occurred.
$ at 1800 myshell myscript EOT job ... at ... $
- This sequence can be used at a terminal:
at −m 0730 tomorrow sort < file >outfile EOT
- 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 !
- 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
- 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'
at 1200 friday
TZ= at noon ...