1AT(P) POSIX Programmer's Manual AT(P)
2
6 at - execute commands at a later time
7
9 at [-m][-f file][-q queuename] -t time_arg
10 at [-m][-f file][-q queuename] timespec ...
12 at -r at_job_id ...
14 at -l -q queuename
16 at -l [at_job_id ...]
18
21 The at utility shall read commands from standard input and group them
22 together as an at-job, to be executed at a later time.
23 The at-job shall be executed in a separate invocation of the shell,
25 running in a separate process group with no controlling terminal,
26 except that the environment variables, current working directory, file
27 creation mask, and other implementation-defined execution-time
28 attributes in effect when the at utility is executed shall be retained
29 and used when the at-job is executed.
30 When the at-job is submitted, the at_job_id and scheduled time shall be
32 written to standard error. The at_job_id is an identifier that shall be
33 a string consisting solely of alphanumeric characters and the period
34 character. The at_job_id shall be assigned by the system when the job
35 is scheduled such that it uniquely identifies a particular job.
36 User notification and the processing of the job's standard output and
38 standard error are described under the -m option.
39 Users shall be permitted to use at if their name appears in the file
41 /usr/lib/cron/at.allow. If that file does not exist, the file
42 /usr/lib/cron/at.deny shall be checked to determine whether the user
43 shall be denied access to at. If neither file exists, only a process
44 with the appropriate privileges shall be allowed to submit a job. If
45 only at.deny exists and is empty, global usage shall be permitted. The
46 at.allow and at.deny files shall consist of one user name per line.
47
49 The at utility shall conform to the Base Definitions volume of
50 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
51 The following options shall be supported:
53 -f file
55 Specify the pathname of a file to be used as the source of the
56 at-job, instead of standard input.
57 -l (The letter ell.) Report all jobs scheduled for the invoking
59 user if no at_job_id operands are specified. If at_job_ids are
60 specified, report only information for these jobs. The output
61 shall be written to standard output.
62 -m Send mail to the invoking user after the at-job has run,
64 announcing its completion. Standard output and standard error
65 produced by the at-job shall be mailed to the user as well,
66 unless redirected elsewhere. Mail shall be sent even if the job
67 produces no output.
68 If -m is not used, the job's standard output and standard error shall
70 be provided to the user by means of mail, unless they are redirected
71 elsewhere; if there is no such output to provide, the implementation
72 need not notify the user of the job's completion.
73 -q queuename
75 Specify in which queue to schedule a job for submission. When
77 used with the -l option, limit the search to that particular
78 queue. By default, at-jobs shall be scheduled in queue a. In
79 contrast, queue b shall be reserved for batch jobs; see batch.
80 The meanings of all other queuenames are implementation-defined.
81 If -q is specified along with either of the -t time_arg or time‐
82 spec arguments, the results are unspecified.
83 -r Remove the jobs with the specified at_job_id operands that were
85 previously scheduled by the at utility.
86 -t time_arg
88 Submit the job to be run at the time specified by the time
89 option-argument, which the application shall ensure has the for‐
90 mat as specified by the touch -t time utility.
91
94 The following operands shall be supported:
95 at_job_id
97 The name reported by a previous invocation of the at utility at
98 the time the job was scheduled.
99 timespec
101 Submit the job to be run at the date and time specified. All of
102 the timespec operands are interpreted as if they were separated
103 by <space>s and concatenated, and shall be parsed as described
104 in the grammar at the end of this section. The date and time
105 shall be interpreted as being in the timezone of the user (as
106 determined by the TZ variable), unless a timezone name appears
107 as part of time, below.
108 In the POSIX locale, the following describes the three parts of the
110 time specification string. All of the values from the LC_TIME cate‐
111 gories in the POSIX locale shall be recognized in a case-insensitive
112 manner.
113 time
115 The time can be specified as one, two, or four digits. One-digit
116 and two-digit numbers shall be taken to be hours; four-digit
117 numbers to be hours and minutes. The time can alternatively be
118 specified as two numbers separated by a colon, meaning
119 hour:minute. An AM/PM indication (one of the values from the
120 am_pm keywords in the LC_TIME locale category) can follow the
121 time; otherwise, a 24-hour clock time shall be understood. A
122 timezone name can also follow to further qualify the time. The
123 acceptable timezone names are implementation-defined, except
124 that they shall be case-insensitive and the string utc is sup‐
125 ported to indicate the time is in Coordinated Universal Time. In
126 the POSIX locale, the time field can also be one of the follow‐
127 ing tokens:
128 midnight
130 Indicates the time 12:00 am (00:00).
131 noon
133 Indicates the time 12:00 pm.
134 now
136 Indicates the current day and time. Invoking at <now>
137 shall submit an at-job for potentially immediate execu‐
138 tion (that is, subject only to unspecified scheduling
139 delays).
140 date
143 An optional date can be specified as either a month name (one of
144 the values from the mon or abmon keywords in the LC_TIME locale
145 category) followed by a day number (and possibly year number
146 preceded by a comma), or a day of the week (one of the values
147 from the day or abday keywords in the LC_TIME locale category).
148 In the POSIX locale, two special days shall be recognized:
149 today
151 Indicates the current day.
152 tomorrow
154 Indicates the day following the current day.
155 If no date is given, today shall be assumed if the given time is
158 greater than the current time, and tomorrow shall be assumed if
159 it is less. If the given month is less than the current month
160 (and no year is given), next year shall be assumed.
161 increment
163 The optional increment shall be a number preceded by a plus sign
164 ( '+' ) and suffixed by one of the following: minutes, hours,
165 days, weeks, months, or years. (The singular forms shall also be
166 accepted.) The keyword next shall be equivalent to an increment
167 number of +1. For example, the following are equivalent com‐
168 mands:
169 at 2pm + 1 week
172 at 2pm next week
173 The following grammar describes the precise format of timespec in the
177 POSIX locale. The general conventions for this style of grammar are
178 described in Grammar Conventions . This formal syntax shall take prece‐
179 dence over the preceding text syntax description. The longest possible
180 token or delimiter shall be recognized at a given point. When used in a
181 timespec, white space shall also delimit tokens.
182 %token hr24clock_hr_min
185 %token hr24clock_hour
186 /*
187 An hr24clock_hr_min is a one, two, or four-digit number. A one-digit
188 or two-digit number constitutes an hr24clock_hour. An hr24clock_hour
189 may be any of the single digits [0,9], or may be double digits, ranging
190 from [00,23]. If an hr24clock_hr_min is a four-digit number, the
191 first two digits shall be a valid hr24clock_hour, while the last two
192 represent the number of minutes, from [00,59].
193 */
194 %token wallclock_hr_min
197 %token wallclock_hour
198 /*
199 A wallclock_hr_min is a one, two-digit, or four-digit number.
200 A one-digit or two-digit number constitutes a wallclock_hour.
201 A wallclock_hour may be any of the single digits [1,9], or may
202 be double digits, ranging from [01,12]. If a wallclock_hr_min
203 is a four-digit number, the first two digits shall be a valid
204 wallclock_hour, while the last two represent the number of
205 minutes, from [00,59].
206 */
207 %token minute
210 /*
211 A minute is a one or two-digit number whose value can be [0,9]
212 or [00,59].
213 */
214 %token day_number
217 /*
218 A day_number is a number in the range appropriate for the particular
219 month and year specified by month_name and year_number, respectively.
220 If no year_number is given, the current year is assumed if the given
221 date and time are later this year. If no year_number is given and
222 the date and time have already occurred this year and the month is
223 not the current month, next year is the assumed year.
224 */
225 %token year_number
228 /*
229 A year_number is a four-digit number representing the year A.D., in
230 which the at_job is to be run.
231 */
232 %token inc_number
235 /*
236 The inc_number is the number of times the succeeding increment
237 period is to be added to the specified date and time.
238 */
239 %token timezone_name
242 /*
243 The name of an optional timezone suffix to the time field, in an
244 implementation-defined format.
245 */
246 %token month_name
249 /*
250 One of the values from the mon or abmon keywords in the LC_TIME
251 locale category.
252 */
253 %token day_of_week
256 /*
257 One of the values from the day or abday keywords in the LC_TIME
258 locale category.
259 */
260 %token am_pm
263 /*
264 One of the values from the am_pm keyword in the LC_TIME locale
265 category.
266 */
267 %start timespec
270 %%
271 timespec : time
272 | time date
273 | time increment
274 | time date increment
275 | nowspec
276 ;
277 nowspec : "now"
280 | "now" increment
281 ;
282 time : hr24clock_hr_min
285 | hr24clock_hr_min timezone_name
286 | hr24clock_hour ":" minute
287 | hr24clock_hour ":" minute timezone_name
288 | wallclock_hr_min am_pm
289 | wallclock_hr_min am_pm timezone_name
290 | wallclock_hour ":" minute am_pm
291 | wallclock_hour ":" minute am_pm timezone_name
292 | "noon"
293 | "midnight"
294 ;
295 date : month_name day_number
298 | month_name day_number "," year_number
299 | day_of_week
300 | "today"
301 | "tomorrow"
302 ;
303 increment : "+" inc_number inc_period
306 | "next" inc_period
307 ;
308 inc_period : "minute" | "minutes"
311 | "hour" | "hours"
312 | "day" | "days"
313 | "week" | "weeks"
314 | "month" | "months"
315 | "year" | "years"
316 ;
317
319 The standard input shall be a text file consisting of commands accept‐
320 able to the shell command language described in Shell Command Language
321 . The standard input shall only be used if no -f file option is speci‐
322 fied.
323
325 See the STDIN section.
326 The text files /usr/lib/cron/at.allow and /usr/lib/cron/at.deny shall
328 contain zero or more user names, one per line, of users who are,
329 respectively, authorized or denied access to the at and batch utili‐
330 ties.
331
333 The following environment variables shall affect the execution of at:
334 LANG Provide a default value for the internationalization variables
336 that are unset or null. (See the Base Definitions volume of
337 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
338 ables for the precedence of internationalization variables used
339 to determine the values of locale categories.)
340 LC_ALL If set to a non-empty string value, override the values of all
342 the other internationalization variables.
343 LC_CTYPE
345 Determine the locale for the interpretation of sequences of
346 bytes of text data as characters (for example, single-byte as
347 opposed to multi-byte characters in arguments and input files).
348 LC_MESSAGES
350 Determine the locale that should be used to affect the format
351 and contents of diagnostic messages written to standard error
352 and informative messages written to standard output.
353 NLSPATH
355 Determine the location of message catalogs for the processing of
356 LC_MESSAGES .
357 LC_TIME
359 Determine the format and contents for date and time strings
360 written and accepted by at.
361 SHELL Determine a name of a command interpreter to be used to invoke
363 the at-job. If the variable is unset or null, sh shall be used.
364 If it is set to a value other than a name for sh, the implemen‐
365 tation shall do one of the following: use that shell; use sh;
366 use the login shell from the user database; or any of the pre‐
367 ceding accompanied by a warning diagnostic about which was cho‐
368 sen.
369 TZ Determine the timezone. The job shall be submitted for execution
371 at the time specified by timespec or -t time relative to the
372 timezone specified by the TZ variable. If timespec specifies a
373 timezone, it shall override TZ . If timespec does not specify a
374 timezone and TZ is unset or null, an unspecified default time‐
375 zone shall be used.
376
379 Default.
380
382 When standard input is a terminal, prompts of unspecified format for
383 each line of the user input described in the STDIN section may be writ‐
384 ten to standard output.
385 In the POSIX locale, the following shall be written to the standard
387 output for each job when jobs are listed in response to the -l option:
388 "%s\t%s\n", at_job_id, <date>
391 where date shall be equivalent in format to the output of:
393 date +"%a %b %e %T %Y"
396 The date and time written shall be adjusted so that they appear in the
398 timezone of the user (as determined by the TZ variable).
399
401 In the POSIX locale, the following shall be written to standard error
402 when a job has been successfully submitted:
403 "job %s at %s\n", at_job_id, <date>
406 where date has the same format as that described in the STDOUT section.
408 Neither this, nor warning messages concerning the selection of the com‐
409 mand interpreter, shall be considered a diagnostic that changes the
410 exit status.
411 Diagnostic messages, if any, shall be written to standard error.
413
415 None.
416
418 None.
419
421 The following exit values shall be returned:
422 0 The at utility successfully submitted, removed, or listed a job
424 or jobs.
425 >0 An error occurred.
427
430 The job shall not be scheduled, removed, or listed.
431 The following sections are informative.
433
435 The format of the at command line shown here is guaranteed only for the
436 POSIX locale. Other cultures may be supported with substantially dif‐
437 ferent interfaces, although implementations are encouraged to provide
438 comparable levels of functionality.
439 Since the commands run in a separate shell invocation, running in a
441 separate process group with no controlling terminal, open file descrip‐
442 tors, traps, and priority inherited from the invoking environment are
443 lost.
444 Some implementations do not allow substitution of different shells
446 using SHELL . System V systems, for example, have used the login shell
447 value for the user in /etc/passwd. To select reliably another command
448 interpreter, the user must include it as part of the script, such as:
449 $ at 1800
452 myshell myscript
453 EOT
454 job ... at ...
455 $
456
458 1. This sequence can be used at a terminal:
459 at -m 0730 tomorrow
462 sort < file >outfile
463 EOT
464 2. This sequence, which demonstrates redirecting standard error to a
466 pipe, is useful in a command procedure (the sequence of output re‐
467 direction specifications is significant):
468 at now + 1 hour <<!
471 diff file1 file2 2>&1 >outfile | mailx mygroup
472 !
473 3. To have a job reschedule itself, at can be invoked from within the
475 at-job. For example, this daily processing script named my.daily
476 runs every day (although crontab is a more appropriate vehicle for
477 such work):
478 # my.daily runs every day
481 daily processingat now tomorrow < my.daily
482 4. The spacing of the three portions of the POSIX locale timespec is
484 quite flexible as long as there are no ambiguities. Examples of
485 various times and operand presentation include:
486 at 0815am Jan 24
489 at 8 :15amjan24
490 at now "+ 1day"
491 at 5 pm FRIday
492 at '17
493 utc+
494 30minutes'
495
497 The at utility reads from standard input the commands to be executed at
498 a later time. It may be useful to redirect standard output and standard
499 error within the specified commands.
500 The -t time option was added as a new capability to support an interna‐
502 tionalized way of specifying a time for execution of the submitted job.
503 Early proposals added a "jobname" concept as a way of giving submitted
505 jobs names that are meaningful to the user submitting them. The histor‐
506 ical, system-specified at_job_id gives no indication of what the job
507 is. Upon further reflection, it was decided that the benefit of this
508 was not worth the change in historical interface. The at functionality
509 is useful in simple environments, but in large or complex situations,
510 the functionality provided by the Batch Services option is more suit‐
511 able.
512 The -q option historically has been an undocumented option, used mainly
514 by the batch utility.
515 The System V -m option was added to provide a method for informing
517 users that an at-job had completed. Otherwise, users are only informed
518 when output to standard error or standard output are not redirected.
519 The behavior of at <now> was changed in an early proposal from being
521 unspecified to submitting a job for potentially immediate execution.
522 Historical BSD at implementations support this. Historical System V
523 implementations give an error in that case, but a change to the System
524 V versions should have no backwards-compatibility ramifications.
525 On BSD-based systems, a -u user option has allowed those with appropri‐
527 ate privileges to access the work of other users. Since this is primar‐
528 ily a system administration feature and is not universally implemented,
529 it has been omitted. Similarly, a specification for the output format
530 for a user with appropriate privileges viewing the queues of other
531 users has been omitted.
532 The -f file option from System V is used instead of the BSD method of
534 using the last operand as the pathname. The BSD method is ambiguous-
535 does:
536 at 1200 friday
539 mean the same thing if there is a file named friday in the current
541 directory?
542 The at_job_id is composed of a limited character set in historical
544 practice, and it is mandated here to invalidate systems that might try
545 using characters that require shell quoting or that could not be easily
546 parsed by shell scripts.
547 The at utility varies between System V and BSD systems in the way time‐
549 zones are used. On System V systems, the TZ variable affects the at-job
550 submission times and the times displayed for the user. On BSD systems,
551 TZ is not taken into account. The BSD behavior is easily achieved with
552 the current specification. If the user wishes to have the timezone
553 default to that of the system, they merely need to issue the at command
554 immediately following an unsetting or null assignment to TZ . For exam‐
555 ple:
556 TZ= at noon ...
559 gives the desired BSD result.
561 While the yacc-like grammar specified in the OPERANDS section is lexi‐
563 cally unambiguous with respect to the digit strings, a lexical analyzer
564 would probably be written to look for and return digit strings in those
565 cases. The parser could then check whether the digit string returned is
566 a valid day_number, year_number, and so on, based on the context.
567
569 None.
570
572 batch , crontab
573
575 Portions of this text are reprinted and reproduced in electronic form
576 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
577 -- Portable Operating System Interface (POSIX), The Open Group Base
578 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
579 Electrical and Electronics Engineers, Inc and The Open Group. In the
580 event of any discrepancy between this version and the original IEEE and
581 The Open Group Standard, the original IEEE and The Open Group Standard
582 is the referee document. The original Standard can be obtained online
583 at http://www.opengroup.org/unix/online.html .
584IEEE/The Open Group 2003 AT(P)