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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>at</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_000_077"> </a>NAME</h4><blockquote>at - execute commands at a later time</blockquote><h4><a name = "tag_000_000_078"> </a>SYNOPSIS</h4><blockquote><pre><code>at <b>[</b>-m<b>][</b>-f <i>file</i><b>][</b>-q <i>queuename</i><b>] </b>-t <i>time</i>at <b>[</b>-m<b>][</b>-f <i>file</i><b>][</b>-q <i>queuename</i><b>] </b><i>timespec</i> ...at -r <i>at_job_id</i> ...at -l -q <i>queuename</i>at -l <b>[</b><i>at_job_id</i> ...<b>]</b></code></pre></blockquote><h4><a name = "tag_000_000_079"> </a>DESCRIPTION</h4><blockquote>The<i>at</i>utility reads commands from standard input andgroups them together as an<i>at-job ,</i>to be executed at a later time.<p>The at-job will be executed in a separateinvocation of the shell, running in a separate process groupwith no controlling terminal, except thatthe environment variables, current working directory,file creation mask and other implementation-dependentexecution-time attributesin effect when the<i>at</i>utility is executedwill be retained and used when the at-job is executed.<p>When the at-job is submitted, the<i>at_job_id</i>and scheduled time are written tostandard error.The<i>at_job_id</i>is an identifier that will be a string consisting solelyof alphanumeric characters and the period character.The<i>at_job_id</i>is assigned by the system when the job is scheduledsuch that it uniquely identifies a particular job.<p>User notification and the processing of the job'sstandard output and standard error are described under the<b>-m</b>option.<p>Users are permitted to use<i>at</i>if their name appears in the file<b>/usr/lib/cron/at.allow</b>.If that file does not exist, the file<b>/usr/lib/cron/at.deny</b>is checked to determine if the usershould be denied access to<i>at</i>.If neither file exists, only a process with the appropriate privilegesis allowed to submit a job.If only<b>at.deny</b>exists and is empty, global usage is permitted.The<b>at.allow</b>and<b>at.deny</b>files consist of one user name per line.</blockquote><h4><a name = "tag_000_000_080"> </a>OPTIONS</h4><blockquote>The<i>at</i>utility supports the <b>XBD</b> specification, <a href="../xbd/utilconv.html#usg"><b>Utility Syntax Guidelines</b> </a> .<p>The following options are supported:<dl compact><dt><b>-f </b><i>file</i><dd>Specify the pathname of a file to be used as the source of the at-job,instead of standard input.<dt><b>-l</b><dd>(The letter ell.)Report all jobs scheduled for the invoking userif no<i>at_job_id</i>operands are specified.If<i>at_job_id</i>sare specified, report only information for these jobs.The output will be written to standard output.<dt><b>-m</b><dd>Send mail to the invoking user after the at-job has run,announcing its completion.Standard output and standard error produced by the at-jobwill be mailed to the useras well, unless redirected elsewhere.Mail will be sent even if the job produces no output.If<b>-m</b>is not used, the job's standard output and standard errorwill be provided to the user by means of mail, unless they are redirected elsewhere;if there is no such output to provide, the implementationneed not notify the user of the job's completion.<dt><b>-q </b><i>queuename</i><dd>Specify in which queue to schedule a job for submission.When used with the<b>-l</b>option, limit the search to that particular queue.By default, at-jobs will be scheduled in queuea.In contrast, queuebis reserved for batch jobs.(See the<i><a href="batch.html">batch</a></i>utility.)The meanings of all other<i>queuenames</i>are implementation-dependent.<dt><b>-r</b><dd>Remove the jobs with the specified<i>at_job_id</i>operands that were previously scheduled by the<i>at</i>utility.<dt><b>-t </b><i>time</i><dd>Submit the job to be run at the time specified by the<i>time</i>option-argument, which must have the format as specified by the<i><a href="touch.html">touch</a></i>utility.</dl></blockquote><h4><a name = "tag_000_000_081"> </a>OPERANDS</h4><blockquote>The following operands are supported:<dl compact><dt><i>at_job_id</i><dd>The name reported by a previous invocation of the<i>at</i>utility at the time the job was scheduled.<dt><i>timespec</i><dd>Submit the job to be run at the date and time specified.All of the<i>timespec</i>operands are interpreted as if theywere separated byspace charactersand concatenated, andare parsed as describedin the grammar at the end of this section.The date and time are interpreted as beingin the timezone of the user (as determined by the<i>TZ</i>variable), unless a timezone name appears as part of<i>time</i>,below.In the POSIX locale, the following describes the threeparts of the time specification string.All of the values from the LC_TIME categoriesin the POSIX locale are recognisedin a case-insensitive manner.<dl compact><dt><i>time</i><dd>The<i>time</i>can be specified as one, two or four digits.One- and two-digit numbers are taken to be hours,four-digit numbers to be hours and minutes.The time can alternatively be specified as two numbersseparated by a colon, meaning<i>hour</i><b>:</b><i>minute</i>.An AM/PM indication(one of the values from the<b>am_pm</b>keywords in the LC_TIME locale category)can follow the time;otherwise, a 24-hour clock time is understood.A timezone name can also followto further qualify the time.The acceptable timezone names are implementation-dependent,except that they will be case-insensitive and the string<b>utc</b>is supported to indicate the timeis in Coordinated Universal Time.The<i>time</i>field can also be one of the following tokensin the POSIX locale:<dl compact><dt><b>midnight</b><dd>Indicates the time 12:00 am (00:00).<dt><b>noon</b><dd>Indicates the time 12:00 pm.<dt><b>now</b><dd>Indicate the current day and time.Invoking<i>at</i><<i>now</i>>will submit an at-job for potentially immediate execution(that is, subject only tounspecified scheduling delays).</dl><p><dt><i>date</i><dd>An optional<i>date</i>can be specified as eithera month name(one of the values from the<b>mon</b>or<b>abmon</b>keywords in the LC_TIME locale category)followed by a day number(and possibly year number preceded by a comma) ora day of the week(one of the values from the<b>day</b>or<b>abday</b>keywords in the LC_TIME locale category).Two special daysare recognisedin the POSIX locale:<dl compact><dt><b>today</b><dd>Indicates the current day.<dt><b>tomorrow</b><dd>Indicates the day following the current day.</dl><p>If no<i>date</i>is given,<b>today</b>is assumed if the given timeis greater than the current time, and<b>tomorrow</b>is assumed if it is less.If the given month is less than the current month (and no year isgiven), next year is assumed.<p><dt><i>increment</i><dd>The optional<i>increment</i>is a number preceded by a plus sign(+)and suffixed by one of the following:<b>minutes</b>,<b>hours</b>,<b>days</b>,<b>weeks</b>,<b>months</b>or<b>years</b>.(The singular forms will be also accepted.)The keyword<b>next</b>is equivalent to an increment number of+ 1.For example, the following are equivalent commands:<pre><code>at 2pm + 1 weekat 2pm next week</code></pre><p></dl><p></dl><p>The following grammar describes the precise format of<i>timespec</i>in the POSIX locale.The general conventions for this style of grammar are described in<xref href=grammar></xref>.This formal syntax takes precedence overthe preceding text syntax description.The longest possible token or delimiter will be recognisedat a given point.When used in a<i>timespec</i>,white space also delimits tokens.<pre><code>%token hr24clock_hr_min%token hr24clock_hour/* A hr24clock_hr_min is a one, two or four digit number. A one or two digit number constitutes a hr24clock_hour. A hr24clock_hour may be any of the single digits '0' - '9', or may be double digits, ranging from "00" - "23". If a hr24clock_hr_min is a four digit number, the first two digits must 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 or four digit number. A one 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 must 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 values 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.*/⌨️ 快捷键说明
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