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
12 at - execute commands at a later time
13
15 at [-m][-f file][-q queuename] -t time_arg
16 at [-m][-f file][-q queuename] timespec ...
18 at -r at_job_id ...
20 at -l -q queuename
22 at -l [at_job_id ...]
24
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 /usr/lib/cron/at.allow. If that file does not exist, the file
48 /usr/lib/cron/at.deny shall be checked to determine whether the user
49 shall be denied access to at. If neither file exists, only a process
50 with the appropriate privileges shall be allowed to submit a job. If
51 only at.deny exists and is empty, global usage shall be permitted. The
52 at.allow and at.deny files shall consist of one user name per line.
53
55 The at utility shall conform to the Base Definitions volume of
56 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
57 The following options shall be supported:
59 -f file
61 Specify the pathname of a file to be used as the source of the
62 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 are
66 specified, report only information for these jobs. The output
67 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 job
73 produces no output.
74 If -m is not used, the job's standard output and standard error shall
76 be provided to the user by means of mail, unless they are redirected
77 elsewhere; if there is no such output to provide, the implementation
78 need not notify the user of the job's completion.
79 -q queuename
81 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 batch.
86 The meanings of all other queuenames are implementation-defined.
87 If -q is specified along with either of the -t time_arg or time‐
88 spec arguments, the results are unspecified.
89 -r Remove the jobs with the specified at_job_id operands that were
91 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 for‐
96 mat as specified by the touch -t time utility.
97
100 The following operands shall be supported:
101 at_job_id
103 The name reported by a previous invocation of the at utility at
104 the time the job was scheduled.
105 timespec
107 Submit the job to be run at the date and time specified. All of
108 the timespec operands are interpreted as if they were separated
109 by <space>s and concatenated, and shall be parsed as described
110 in the grammar at the end of this section. The date and time
111 shall be interpreted as being in the timezone of the user (as
112 determined by the TZ variable), unless a timezone name appears
113 as part of time, below.
114 In the POSIX locale, the following describes the three parts of the
116 time specification string. All of the values from the LC_TIME cate‐
117 gories in the POSIX locale shall be recognized in a case-insensitive
118 manner.
119 time
121 The time can be specified as one, two, or four digits. One-digit
122 and two-digit numbers shall be taken to be hours; four-digit
123 numbers to be hours and minutes. The time can alternatively be
124 specified as two numbers separated by a colon, meaning
125 hour:minute. An AM/PM indication (one of the values from the
126 am_pm keywords in the LC_TIME locale category) can follow the
127 time; otherwise, a 24-hour clock time shall be understood. A
128 timezone name can also follow to further qualify the time. The
129 acceptable timezone names are implementation-defined, except
130 that they shall be case-insensitive and the string utc is sup‐
131 ported to indicate the time is in Coordinated Universal Time. In
132 the POSIX locale, the time field can also be one of the follow‐
133 ing tokens:
134 midnight
136 Indicates the time 12:00 am (00:00).
137 noon
139 Indicates the time 12:00 pm.
140 now
142 Indicates the current day and time. Invoking at <now>
143 shall submit an at-job for potentially immediate execu‐
144 tion (that is, subject only to unspecified scheduling
145 delays).
146 date
149 An optional date can be specified as either a month name (one of
150 the values from the mon or abmon keywords in the LC_TIME locale
151 category) followed by a day number (and possibly year number
152 preceded by a comma), or a day of the week (one of the values
153 from the day or abday keywords in the LC_TIME locale category).
154 In the POSIX locale, two special days shall be recognized:
155 today
157 Indicates the current day.
158 tomorrow
160 Indicates the day following the current day.
161 If no date is given, today shall be assumed if the given time is
164 greater than the current time, and tomorrow shall be assumed if
165 it is less. If the given month is less than the current month
166 (and no year is given), next year shall be assumed.
167 increment
169 The optional increment shall be a number preceded by a plus sign
170 ( '+' ) and suffixed by one of the following: minutes, hours,
171 days, weeks, months, or years. (The singular forms shall also be
172 accepted.) The keyword next shall be equivalent to an increment
173 number of +1. For example, the following are equivalent com‐
174 mands:
175 at 2pm + 1 week
178 at 2pm next week
179 The following grammar describes the precise format of timespec in the
183 POSIX locale. The general conventions for this style of grammar are
184 described in Grammar Conventions . This formal syntax shall take prece‐
185 dence over the preceding text syntax description. The longest possible
186 token or delimiter shall be recognized at a given point. When used in a
187 timespec, white space shall also delimit tokens.
188 %token hr24clock_hr_min
191 %token hr24clock_hour
192 /*
193 An hr24clock_hr_min is a one, two, or four-digit number. A one-digit
194 or two-digit number constitutes an hr24clock_hour. An hr24clock_hour
195 may be any of the single digits [0,9], or may be double digits, ranging
196 from [00,23]. If an hr24clock_hr_min is a four-digit number, the
197 first two digits shall be a valid hr24clock_hour, while the last two
198 represent the number of minutes, from [00,59].
199 */
200 %token wallclock_hr_min
203 %token wallclock_hour
204 /*
205 A wallclock_hr_min is a one, two-digit, or four-digit number.
206 A one-digit or two-digit number constitutes a wallclock_hour.
207 A wallclock_hour may be any of the single digits [1,9], or may
208 be double digits, ranging from [01,12]. If a wallclock_hr_min
209 is a four-digit number, the first two digits shall be a valid
210 wallclock_hour, while the last two represent the number of
211 minutes, from [00,59].
212 */
213 %token minute
216 /*
217 A minute is a one or two-digit number whose value can be [0,9]
218 or [00,59].
219 */
220 %token day_number
223 /*
224 A day_number is a number in the range appropriate for the particular
225 month and year specified by month_name and year_number, respectively.
226 If no year_number is given, the current year is assumed if the given
227 date and time are later this year. If no year_number is given and
228 the date and time have already occurred this year and the month is
229 not the current month, next year is the assumed year.
230 */
231 %token year_number
234 /*
235 A year_number is a four-digit number representing the year A.D., in
236 which the at_job is to be run.
237 */
238 %token inc_number
241 /*
242 The inc_number is the number of times the succeeding increment
243 period is to be added to the specified date and time.
244 */
245 %token timezone_name
248 /*
249 The name of an optional timezone suffix to the time field, in an
250 implementation-defined format.
251 */
252 %token month_name
255 /*
256 One of the values from the mon or abmon keywords in the LC_TIME
257 locale category.
258 */
259 %token day_of_week
262 /*
263 One of the values from the day or abday keywords in the LC_TIME
264 locale category.
265 */
266 %token am_pm
269 /*
270 One of the values from the am_pm keyword in the LC_TIME locale
271 category.
272 */
273 %start timespec
276 %%
277 timespec : time
278 | time date
279 | time increment
280 | time date increment
281 | nowspec
282 ;
283 nowspec : "now"
286 | "now" increment
287 ;
288 time : hr24clock_hr_min
291 | hr24clock_hr_min timezone_name
292 | hr24clock_hour ":" minute
293 | hr24clock_hour ":" minute timezone_name
294 | wallclock_hr_min am_pm
295 | wallclock_hr_min am_pm timezone_name
296 | wallclock_hour ":" minute am_pm
297 | wallclock_hour ":" minute am_pm timezone_name
298 | "noon"
299 | "midnight"
300 ;
301 date : month_name day_number
304 | month_name day_number "," year_number
305 | day_of_week
306 | "today"
307 | "tomorrow"
308 ;
309 increment : "+" inc_number inc_period
312 | "next" inc_period
313 ;
314 inc_period : "minute" | "minutes"
317 | "hour" | "hours"
318 | "day" | "days"
319 | "week" | "weeks"
320 | "month" | "months"
321 | "year" | "years"
322 ;
323
325 The standard input shall be a text file consisting of commands accept‐
326 able to the shell command language described in Shell Command Language
327 . The standard input shall only be used if no -f file option is speci‐
328 fied.
329
331 See the STDIN section.
332 The text files /usr/lib/cron/at.allow and /usr/lib/cron/at.deny shall
334 contain zero or more user names, one per line, of users who are,
335 respectively, authorized or denied access to the at and batch utili‐
336 ties.
337
339 The following environment variables shall affect the execution of at:
340 LANG Provide a default value for the internationalization variables
342 that are unset or null. (See the Base Definitions volume of
343 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
344 ables for the precedence of internationalization variables used
345 to determine the values of locale categories.)
346 LC_ALL If set to a non-empty string value, override the values of all
348 the other internationalization variables.
349 LC_CTYPE
351 Determine the locale for the interpretation of sequences of
352 bytes of text data as characters (for example, single-byte as
353 opposed to multi-byte characters in arguments and input files).
354 LC_MESSAGES
356 Determine the locale that should be used to affect the format
357 and contents of diagnostic messages written to standard error
358 and informative messages written to standard output.
359 NLSPATH
361 Determine the location of message catalogs for the processing of
362 LC_MESSAGES .
363 LC_TIME
365 Determine the format and contents for date and time strings
366 written and accepted by at.
367 SHELL Determine a name of a command interpreter to be used to invoke
369 the at-job. If the variable is unset or null, sh shall be used.
370 If it is set to a value other than a name for sh, the implemen‐
371 tation shall do one of the following: use that shell; use sh;
372 use the login shell from the user database; or any of the pre‐
373 ceding accompanied by a warning diagnostic about which was cho‐
374 sen.
375 TZ Determine the timezone. The job shall be submitted for execution
377 at the time specified by timespec or -t time relative to the
378 timezone specified by the TZ variable. If timespec specifies a
379 timezone, it shall override TZ. If timespec does not specify a
380 timezone and TZ is unset or null, an unspecified default time‐
381 zone shall be used.
382
385 Default.
386
388 When standard input is a terminal, prompts of unspecified format for
389 each line of the user input described in the STDIN section may be writ‐
390 ten to standard output.
391 In the POSIX locale, the following shall be written to the standard
393 output for each job when jobs are listed in response to the -l option:
394 "%s\t%s\n", at_job_id, <date>
397 where date shall be equivalent in format to the output of:
399 date +"%a %b %e %T %Y"
402 The date and time written shall be adjusted so that they appear in the
404 timezone of the user (as determined by the TZ variable).
405
407 In the POSIX locale, the following shall be written to standard error
408 when a job has been successfully submitted:
409 "job %s at %s\n", at_job_id, <date>
412 where date has the same format as that described in the STDOUT section.
414 Neither this, nor warning messages concerning the selection of the com‐
415 mand interpreter, shall be considered a diagnostic that changes the
416 exit status.
417 Diagnostic messages, if any, shall be written to standard error.
419
421 None.
422
424 None.
425
427 The following exit values shall be returned:
428 0 The at utility successfully submitted, removed, or listed a job
430 or jobs.
431 >0 An error occurred.
433
436 The job shall not be scheduled, removed, or listed.
437 The following sections are informative.
439
441 The format of the at command line shown here is guaranteed only for the
442 POSIX locale. Other cultures may be supported with substantially dif‐
443 ferent interfaces, although implementations are encouraged to provide
444 comparable levels of functionality.
445 Since the commands run in a separate shell invocation, running in a
447 separate process group with no controlling terminal, open file descrip‐
448 tors, traps, and priority inherited from the invoking environment are
449 lost.
450 Some implementations do not allow substitution of different shells
452 using SHELL. System V systems, for example, have used the login shell
453 value for the user in /etc/passwd. To select reliably another command
454 interpreter, the user must include it as part of the script, such as:
455 $ at 1800
458 myshell myscript
459 EOT
460 job ... at ...
461 $
462
464 1. This sequence can be used at a terminal:
465 at -m 0730 tomorrow
468 sort < file >outfile
469 EOT
470 2. This sequence, which demonstrates redirecting standard error to a
472 pipe, is useful in a command procedure (the sequence of output re‐
473 direction specifications is significant):
474 at now + 1 hour <<!
477 diff file1 file2 2>&1 >outfile | mailx mygroup
478 !
479 3. To have a job reschedule itself, at can be invoked from within the
481 at-job. For example, this daily processing script named my.daily
482 runs every day (although crontab is a more appropriate vehicle for
483 such work):
484 # my.daily runs every day
487 daily processingat now tomorrow < my.daily
488 4. The spacing of the three portions of the POSIX locale timespec is
490 quite flexible as long as there are no ambiguities. Examples of
491 various times and operand presentation include:
492 at 0815am Jan 24
495 at 8 :15amjan24
496 at now "+ 1day"
497 at 5 pm FRIday
498 at '17
499 utc+
500 30minutes'
501
503 The at utility reads from standard input the commands to be executed at
504 a later time. It may be useful to redirect standard output and standard
505 error within the specified commands.
506 The -t time option was added as a new capability to support an interna‐
508 tionalized way of specifying a time for execution of the submitted job.
509 Early proposals added a "jobname" concept as a way of giving submitted
511 jobs names that are meaningful to the user submitting them. The histor‐
512 ical, system-specified at_job_id gives no indication of what the job
513 is. Upon further reflection, it was decided that the benefit of this
514 was not worth the change in historical interface. The at functionality
515 is useful in simple environments, but in large or complex situations,
516 the functionality provided by the Batch Services option is more suit‐
517 able.
518 The -q option historically has been an undocumented option, used mainly
520 by the batch utility.
521 The System V -m option was added to provide a method for informing
523 users that an at-job had completed. Otherwise, users are only informed
524 when output to standard error or standard output are not redirected.
525 The behavior of at <now> was changed in an early proposal from being
527 unspecified to submitting a job for potentially immediate execution.
528 Historical BSD at implementations support this. Historical System V
529 implementations give an error in that case, but a change to the System
530 V versions should have no backwards-compatibility ramifications.
531 On BSD-based systems, a -u user option has allowed those with appropri‐
533 ate privileges to access the work of other users. Since this is primar‐
534 ily a system administration feature and is not universally implemented,
535 it has been omitted. Similarly, a specification for the output format
536 for a user with appropriate privileges viewing the queues of other
537 users has been omitted.
538 The -f file option from System V is used instead of the BSD method of
540 using the last operand as the pathname. The BSD method is ambiguous-
541 does:
542 at 1200 friday
545 mean the same thing if there is a file named friday in the current
547 directory?
548 The at_job_id is composed of a limited character set in historical
550 practice, and it is mandated here to invalidate systems that might try
551 using characters that require shell quoting or that could not be easily
552 parsed by shell scripts.
553 The at utility varies between System V and BSD systems in the way time‐
555 zones are used. On System V systems, the TZ variable affects the at-job
556 submission times and the times displayed for the user. On BSD systems,
557 TZ is not taken into account. The BSD behavior is easily achieved with
558 the current specification. If the user wishes to have the timezone
559 default to that of the system, they merely need to issue the at command
560 immediately following an unsetting or null assignment to TZ . For exam‐
561 ple:
562 TZ= at noon ...
565 gives the desired BSD result.
567 While the yacc-like grammar specified in the OPERANDS section is lexi‐
569 cally unambiguous with respect to the digit strings, a lexical analyzer
570 would probably be written to look for and return digit strings in those
571 cases. The parser could then check whether the digit string returned is
572 a valid day_number, year_number, and so on, based on the context.
573
575 None.
576
578 batch, crontab
579
581 Portions of this text are reprinted and reproduced in electronic form
582 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
583 -- Portable Operating System Interface (POSIX), The Open Group Base
584 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
585 Electrical and Electronics Engineers, Inc and The Open Group. In the
586 event of any discrepancy between this version and the original IEEE and
587 The Open Group Standard, the original IEEE and The Open Group Standard
588 is the referee document. The original Standard can be obtained online
589 at http://www.opengroup.org/unix/online.html .
590IEEE/The Open Group 2003 AT(1P)