1AT(1P) POSIX Programmer's Manual AT(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 at — execute commands at a later time
14
16 at [−m] [−f file] [−q queuename] −t time_arg
17 at [−m] [−f file] [−q queuename] timespec...
19 at −r at_job_id...
21 at −l −q queuename
23 at −l [at_job_id...]
25
27 The at utility shall read commands from standard input and group them
28 together as an at-job, to be executed at a later time.
29 The at-job shall be executed in a separate invocation of the shell,
31 running in a separate process group with no controlling terminal,
32 except that the environment variables, current working directory, file
33 creation mask, and other implementation-defined execution-time
34 attributes in effect when the at utility is executed shall be retained
35 and used when the at-job is executed.
36 When the at-job is submitted, the at_job_id and scheduled time shall be
38 written to standard error. The at_job_id is an identifier that shall be
39 a string consisting solely of alphanumeric characters and the <period>
40 character. The at_job_id shall be assigned by the system when the job
41 is scheduled such that it uniquely identifies a particular job.
42 User notification and the processing of the job's standard output and
44 standard error are described under the −m option.
45 Users shall be permitted to use at if their name appears in the file
47 at.allow which is located in an implementation-defined directory. If
48 that file does not exist, the file at.deny, which is located in an
49 implementation-defined directory, shall be checked to determine whether
50 the user shall be denied access to at. If neither file exists, only a
51 process with appropriate privileges shall be allowed to submit a job.
52 If only at.deny exists and is empty, global usage shall be permitted.
53 The at.allow and at.deny files shall consist of one user name per line.
54
56 The at utility shall conform to the Base Definitions volume of
57 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
58 The following options shall be supported:
60 −f file Specify the pathname of a file to be used as the source of
62 the at-job, instead of standard input.
63 −l (The letter ell.) Report all jobs scheduled for the invoking
65 user if no at_job_id operands are specified. If at_job_ids
66 are specified, report only information for these jobs. The
67 output shall be written to standard output.
68 −m Send mail to the invoking user after the at-job has run,
70 announcing its completion. Standard output and standard error
71 produced by the at-job shall be mailed to the user as well,
72 unless redirected elsewhere. Mail shall be sent even if the
73 job produces no output.
74 If −m is not used, the job's standard output and standard
76 error shall be provided to the user by means of mail, unless
77 they are redirected elsewhere; if there is no such output to
78 provide, the implementation need not notify the user of the
79 job's completion.
80 −q queuename
82 Specify in which queue to schedule a job for submission. When
83 used with the −l option, limit the search to that particular
84 queue. By default, at-jobs shall be scheduled in queue a. In
85 contrast, queue b shall be reserved for batch jobs; see
86 batch. The meanings of all other queuenames are implementa‐
87 tion-defined. If −q is specified along with either of the −t
88 time_arg or timespec arguments, the results are unspecified.
89 −r Remove the jobs with the specified at_job_id operands that
91 were previously scheduled by the at utility.
92 −t time_arg
94 Submit the job to be run at the time specified by the time
95 option-argument, which the application shall ensure has the
96 format as specified by the touch −t time utility.
97
99 The following operands shall be supported:
100 at_job_id The name reported by a previous invocation of the at utility
102 at the time the job was scheduled.
103 timespec Submit the job to be run at the date and time specified. All
105 of the timespec operands are interpreted as if they were sep‐
106 arated by <space> characters and concatenated, and shall be
107 parsed as described in the grammar at the end of this sec‐
108 tion. The date and time shall be interpreted as being in the
109 timezone of the user (as determined by the TZ variable),
110 unless a timezone name appears as part of time, below.
111 In the POSIX locale, the following describes the three parts
113 of the time specification string. All of the values from the
114 LC_TIME categories in the POSIX locale shall be recognized in
115 a case-insensitive manner.
116 time The time can be specified as one, two, or four dig‐
118 its. One-digit and two-digit numbers shall be taken
119 to be hours; four-digit numbers to be hours and
120 minutes. The time can alternatively be specified as
121 two numbers separated by a <colon>, meaning
122 hour:minute. An AM/PM indication (one of the values
123 from the am_pm keywords in the LC_TIME locale cate‐
124 gory) can follow the time; otherwise, a 24-hour
125 clock time shall be understood. A timezone name can
126 also follow to further qualify the time. The
127 acceptable timezone names are implementation-
128 defined, except that they shall be case-insensitive
129 and the string utc is supported to indicate the
130 time is in Coordinated Universal Time. In the
131 POSIX locale, the time field can also be one of the
132 following tokens:
133 midnight Indicates the time 12:00 am (00:00).
135 noon Indicates the time 12:00 pm.
137 now Indicates the current day and time.
139 Invoking at <now> shall submit an at-job
140 for potentially immediate execution (that
141 is, subject only to unspecified schedul‐
142 ing delays).
143 date An optional date can be specified as either a month
145 name (one of the values from the mon or abmon key‐
146 words in the LC_TIME locale category) followed by a
147 day number (and possibly year number preceded by a
148 comma), or a day of the week (one of the values
149 from the day or abday keywords in the LC_TIME
150 locale category). In the POSIX locale, two special
151 days shall be recognized:
152 today Indicates the current day.
154 tomorrow Indicates the day following the current
156 day.
157 If no date is given, today shall be assumed if the
159 given time is greater than the current time, and
160 tomorrow shall be assumed if it is less. If the
161 given month is less than the current month (and no
162 year is given), next year shall be assumed.
163 increment The optional increment shall be a number preceded
165 by a <plus-sign> ('+') and suffixed by one of the
166 following: minutes, hours, days, weeks, months, or
167 years. (The singular forms shall also be
168 accepted.) The keyword next shall be equivalent to
169 an increment number of +1. For example, the follow‐
170 ing are equivalent commands:
171 at 2pm + 1 week
173 at 2pm next week
174 The following grammar describes the precise format of timespec in the
176 POSIX locale. The general conventions for this style of grammar are
177 described in Section 1.3, Grammar Conventions. This formal syntax
178 shall take precedence over the preceding text syntax description. The
179 longest possible token or delimiter shall be recognized at a given
180 point. When used in a timespec, white space shall also delimit tokens.
181 %token hr24clock_hr_min
183 %token hr24clock_hour
184 /*
185 An hr24clock_hr_min is a one, two, or four-digit number. A one-digit
186 or two-digit number constitutes an hr24clock_hour. An hr24clock_hour
187 may be any of the single digits [0,9], or may be double digits, ranging
188 from [00,23]. If an hr24clock_hr_min is a four-digit number, the
189 first two digits shall be a valid hr24clock_hour, while the last two
190 represent the number of minutes, from [00,59].
191 */
192 %token wallclock_hr_min
194 %token wallclock_hour
195 /*
196 A wallclock_hr_min is a one, two-digit, or four-digit number.
197 A one-digit or two-digit number constitutes a wallclock_hour.
198 A wallclock_hour may be any of the single digits [1,9], or may
199 be double digits, ranging from [01,12]. If a wallclock_hr_min
200 is a four-digit number, the first two digits shall be a valid
201 wallclock_hour, while the last two represent the number of
202 minutes, from [00,59].
203 */
204 %token minute
206 /*
207 A minute is a one or two-digit number whose value can be [0,9]
208 or [00,59].
209 */
210 %token day_number
212 /*
213 A day_number is a number in the range appropriate for the particular
214 month and year specified by month_name and year_number, respectively.
215 If no year_number is given, the current year is assumed if the given
216 date and time are later this year. If no year_number is given and
217 the date and time have already occurred this year and the month is
218 not the current month, next year is the assumed year.
219 */
220 %token year_number
222 /*
223 A year_number is a four-digit number representing the year A.D., in
224 which the at_job is to be run.
225 */
226 %token inc_number
228 /*
229 The inc_number is the number of times the succeeding increment
230 period is to be added to the specified date and time.
231 */
232 %token timezone_name
234 /*
235 The name of an optional timezone suffix to the time field, in an
236 implementation-defined format.
237 */
238 %token month_name
240 /*
241 One of the values from the mon or abmon keywords in the LC_TIME
242 locale category.
243 */
244 %token day_of_week
246 /*
247 One of the values from the day or abday keywords in the LC_TIME
248 locale category.
249 */
250 %token am_pm
252 /*
253 One of the values from the am_pm keyword in the LC_TIME locale
254 category.
255 */
256 %start timespec
258 %%
259 timespec : time
260 | time date
261 | time increment
262 | time date increment
263 | nowspec
264 ;
265 nowspec : "now"
267 | "now" increment
268 ;
269 time : hr24clock_hr_min
271 | hr24clock_hr_min timezone_name
272 | hr24clock_hour ":" minute
273 | hr24clock_hour ":" minute timezone_name
274 | wallclock_hr_min am_pm
275 | wallclock_hr_min am_pm timezone_name
276 | wallclock_hour ":" minute am_pm
277 | wallclock_hour ":" minute am_pm timezone_name
278 | "noon"
279 | "midnight"
280 ;
281 date : month_name day_number
283 | month_name day_number "," year_number
284 | day_of_week
285 | "today"
286 | "tomorrow"
287 ;
288 increment : "+" inc_number inc_period
290 | "next" inc_period
291 ;
292 inc_period : "minute" | "minutes"
294 | "hour" | "hours"
295 | "day" | "days"
296 | "week" | "weeks"
297 | "month" | "months"
298 | "year" | "years"
299 ;
300
302 The standard input shall be a text file consisting of commands accept‐
303 able to the shell command language described in Chapter 2, Shell Com‐
304 mand Language. The standard input shall only be used if no −f file
305 option is specified.
306
308 See the STDIN section.
309 The text files at.allow and at.deny, which are located in an implemen‐
311 tation-defined directory, shall contain zero or more user names, one
312 per line, of users who are, respectively, authorized or denied access
313 to the at and batch utilities.
314
316 The following environment variables shall affect the execution of at:
317 LANG Provide a default value for the internationalization vari‐
319 ables that are unset or null. (See the Base Definitions vol‐
320 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
321 ables for the precedence of internationalization variables
322 used to determine the values of locale categories.)
323 LC_ALL If set to a non-empty string value, override the values of
325 all the other internationalization variables.
326 LC_CTYPE Determine the locale for the interpretation of sequences of
328 bytes of text data as characters (for example, single-byte as
329 opposed to multi-byte characters in arguments and input
330 files).
331 LC_MESSAGES
333 Determine the locale that should be used to affect the format
334 and contents of diagnostic messages written to standard error
335 and informative messages written to standard output.
336 NLSPATH Determine the location of message catalogs for the processing
338 of LC_MESSAGES.
339 LC_TIME Determine the format and contents for date and time strings
341 written and accepted by at.
342 SHELL Determine a name of a command interpreter to be used to
344 invoke the at-job. If the variable is unset or null, sh shall
345 be used. If it is set to a value other than a name for sh,
346 the implementation shall do one of the following: use that
347 shell; use sh; use the login shell from the user database; or
348 any of the preceding accompanied by a warning diagnostic
349 about which was chosen.
350 TZ Determine the timezone. The job shall be submitted for execu‐
352 tion at the time specified by timespec or −t time relative to
353 the timezone specified by the TZ variable. If timespec speci‐
354 fies a timezone, it shall override TZ. If timespec does not
355 specify a timezone and TZ is unset or null, an unspecified
356 default timezone shall be used.
357
359 Default.
360
362 When standard input is a terminal, prompts of unspecified format for
363 each line of the user input described in the STDIN section may be writ‐
364 ten to standard output.
365 In the POSIX locale, the following shall be written to the standard
367 output for each job when jobs are listed in response to the −l option:
368 "%s\t%s\n", at_job_id, <date>
370 where date shall be equivalent in format to the output of:
372 date +"%a %b %e %T %Y"
374 The date and time written shall be adjusted so that they appear in the
376 timezone of the user (as determined by the TZ variable).
377
379 In the POSIX locale, the following shall be written to standard error
380 when a job has been successfully submitted:
381 "job %s at %s\n", at_job_id, <date>
383 where date has the same format as that described in the STDOUT section.
385 Neither this, nor warning messages concerning the selection of the com‐
386 mand interpreter, shall be considered a diagnostic that changes the
387 exit status.
388 Diagnostic messages, if any, shall be written to standard error.
390
392 None.
393
395 None.
396
398 The following exit values shall be returned:
399 0 The at utility successfully submitted, removed, or listed a job
401 or jobs.
402 >0 An error occurred.
404
406 The job shall not be scheduled, removed, or listed.
407 The following sections are informative.
409
411 The format of the at command line shown here is guaranteed only for the
412 POSIX locale. Other cultures may be supported with substantially dif‐
413 ferent interfaces, although implementations are encouraged to provide
414 comparable levels of functionality.
415 Since the commands run in a separate shell invocation, running in a
417 separate process group with no controlling terminal, open file descrip‐
418 tors, traps, and priority inherited from the invoking environment are
419 lost.
420 Some implementations do not allow substitution of different shells
422 using SHELL. System V systems, for example, have used the login shell
423 value for the user in /etc/passwd. To select reliably another command
424 interpreter, the user must include it as part of the script, such as:
425 $ at 1800
427 myshell myscript
428 EOT
429 job ... at ...
430 $
431
433 1. This sequence can be used at a terminal:
434 at −m 0730 tomorrow
436 sort < file >outfile
437 EOT
438 2. This sequence, which demonstrates redirecting standard error to a
440 pipe, is useful in a command procedure (the sequence of output re‐
441 direction specifications is significant):
442 at now + 1 hour <<!
444 diff file1 file2 2>&1 >outfile | mailx mygroup
445 !
446 3. To have a job reschedule itself, at can be invoked from within the
448 at-job. For example, this daily processing script named my.daily
449 runs every day (although crontab is a more appropriate vehicle for
450 such work):
451 # my.daily runs every day
453 daily processing
454 at now tomorrow < my.daily
455 4. The spacing of the three portions of the POSIX locale timespec is
457 quite flexible as long as there are no ambiguities. Examples of
458 various times and operand presentation include:
459 at 0815am Jan 24
461 at 8 :15amjan24
462 at now "+ 1day"
463 at 5 pm FRIday
464 at '17
465 utc+
466 30minutes'
467
469 The at utility reads from standard input the commands to be executed at
470 a later time. It may be useful to redirect standard output and standard
471 error within the specified commands.
472 The −t time option was added as a new capability to support an interna‐
474 tionalized way of specifying a time for execution of the submitted job.
475 Early proposals added a ``jobname'' concept as a way of giving submit‐
477 ted jobs names that are meaningful to the user submitting them. The
478 historical, system-specified at_job_id gives no indication of what the
479 job is. Upon further reflection, it was decided that the benefit of
480 this was not worth the change in historical interface. The at function‐
481 ality is useful in simple environments, but in large or complex situa‐
482 tions, the functionality provided by the Batch Services option is more
483 suitable.
484 The −q option historically has been an undocumented option, used mainly
486 by the batch utility.
487 The System V −m option was added to provide a method for informing
489 users that an at-job had completed. Otherwise, users are only informed
490 when output to standard error or standard output are not redirected.
491 The behavior of at <now> was changed in an early proposal from being
493 unspecified to submitting a job for potentially immediate execution.
494 Historical BSD at implementations support this. Historical System V
495 implementations give an error in that case, but a change to the System
496 V versions should have no backwards-compatibility ramifications.
497 On BSD-based systems, a −u user option has allowed those with appropri‐
499 ate privileges to access the work of other users. Since this is primar‐
500 ily a system administration feature and is not universally implemented,
501 it has been omitted. Similarly, a specification for the output format
502 for a user with appropriate privileges viewing the queues of other
503 users has been omitted.
504 The −f file option from System V is used instead of the BSD method of
506 using the last operand as the pathname. The BSD method is ambiguous—
507 does:
508 at 1200 friday
510 mean the same thing if there is a file named friday in the current
512 directory?
513 The at_job_id is composed of a limited character set in historical
515 practice, and it is mandated here to invalidate systems that might try
516 using characters that require shell quoting or that could not be easily
517 parsed by shell scripts.
518 The at utility varies between System V and BSD systems in the way time‐
520 zones are used. On System V systems, the TZ variable affects the at-job
521 submission times and the times displayed for the user. On BSD systems,
522 TZ is not taken into account. The BSD behavior is easily achieved with
523 the current specification. If the user wishes to have the timezone
524 default to that of the system, they merely need to issue the at command
525 immediately following an unsetting or null assignment to TZ. For exam‐
526 ple:
527 TZ= at noon ...
529 gives the desired BSD result.
531 While the yacc-like grammar specified in the OPERANDS section is lexi‐
533 cally unambiguous with respect to the digit strings, a lexical analyzer
534 would probably be written to look for and return digit strings in those
535 cases. The parser could then check whether the digit string returned is
536 a valid day_number, year_number, and so on, based on the context.
537
539 None.
540
542 batch, crontab
543 The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
545 Variables, Section 12.2, Utility Syntax Guidelines
546
548 Portions of this text are reprinted and reproduced in electronic form
549 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
550 -- Portable Operating System Interface (POSIX), The Open Group Base
551 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
552 cal and Electronics Engineers, Inc and The Open Group. (This is
553 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
554 event of any discrepancy between this version and the original IEEE and
555 The Open Group Standard, the original IEEE and The Open Group Standard
556 is the referee document. The original Standard can be obtained online
557 at http://www.unix.org/online.html .
558 Any typographical or formatting errors that appear in this page are
560 most likely to have been introduced during the conversion of the source
561 files to man page format. To report such errors, see https://www.ker‐
562 nel.org/doc/man-pages/reporting_bugs.html .
563IEEE/The Open Group 2013 AT(1P)