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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>at</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="at"></a> <a name="tag_04_05"></a><!-- at --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_04_05_01"></a>NAME</h4><blockquote>at - execute commands at a later time</blockquote><h4><a name="tag_04_05_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('UP')">UP</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> at</tt> <b>[</b><tt>-m</tt><b>][</b><tt>-f</tt> <i>file</i><b>][</b><tt>-q</tt><i>queuename</i><b>]</b> <tt>-t</tt> <i>time_arg</i><tt><br><br>at</tt> <b>[</b><tt>-m</tt><b>][</b><tt>-f</tt> <i>file</i><b>][</b><tt>-q</tt> <i>queuename</i><b>]</b> <i>timespec</i><tt>...<br><br> at -r</tt> <i>at_job_id</i> <tt>...<br><br> at -l -q</tt> <i>queuename</i><tt><br><br>at -l</tt> <b>[</b><i>at_job_id</i> <tt>...</tt><b>]</b><tt><img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_04_05_03"></a>DESCRIPTION</h4><blockquote><p>The <i>at</i> utility shall read commands from standard input and group them together as an <i>at-job</i>, to be executed at alater time.</p><p>The at-job shall be executed in a separate invocation of the shell, running in a separate process group with no controllingterminal, except that the environment variables, current working directory, file creation mask, and other implementation-definedexecution-time attributes in effect when the <i>at</i> utility is executed shall be retained and used when the at-job isexecuted.</p><p>When the at-job is submitted, the <i>at_job_id</i> and scheduled time shall be written to standard error. The <i>at_job_id</i>is an identifier that shall be a string consisting solely of alphanumeric characters and the period character. The <i>at_job_id</i>shall be assigned by the system when the job is scheduled such that it uniquely identifies a particular job.</p><p>User notification and the processing of the job's standard output and standard error are described under the <b>-m</b>option.</p><p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Users shall be permitted to use <i>at</i> if their name appears in the file <b>/usr/lib/cron/at.allow</b>. If that file does notexist, the file <b>/usr/lib/cron/at.deny</b> shall be checked to determine whether the user shall be denied access to <i>at</i>. Ifneither file exists, only a process with the appropriate privileges shall be allowed to submit a job. If only <b>at.deny</b> existsand is empty, global usage shall be permitted. The <b>at.allow</b> and <b>at.deny</b> files shall consist of one user name perline. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_04_05_04"></a>OPTIONS</h4><blockquote><p>The <i>at</i> utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax Guidelines</a>.</p><p>The following options shall be supported:</p><dl compact><dt><b>-f </b> <i>file</i></dt><dd>Specify the pathname of a file to be used as the source of the at-job, instead of standard input.</dd><dt><b>-l</b></dt><dd>(The letter ell.) Report all jobs scheduled for the invoking user if no <i>at_job_id</i> operands are specified. If<i>at_job_id</i>s are specified, report only information for these jobs. The output shall be written to standard output.</dd><dt><b>-m</b></dt><dd>Send mail to the invoking user after the at-job has run, announcing its completion. Standard output and standard error producedby the at-job shall be mailed to the user as well, unless redirected elsewhere. Mail shall be sent even if the job produces nooutput. <p>If <b>-m</b> is not used, the job's standard output and standard error shall be provided to the user by means of mail, unlessthey are redirected elsewhere; if there is no such output to provide, the implementation need not notify the user of the job'scompletion.</p></dd><dt><b>-q </b> <i>queuename</i></dt><dd><br>Specify in which queue to schedule a job for submission. When used with the <b>-l</b> option, limit the search to that particularqueue. By default, at-jobs shall be scheduled in queue <i>a</i>. In contrast, queue <i>b</i> shall be reserved for batch jobs; see<a href="../utilities/batch.html"><i>batch</i></a>. The meanings of all other <i>queuename</i>s are implementation-defined. If<b>-q</b> is specified along with either of the <b>-t</b> <i>time_arg</i> or <i>timespec</i> arguments, the results areunspecified.</dd><dt><b>-r</b></dt><dd>Remove the jobs with the specified <i>at_job_id</i> operands that were previously scheduled by the <i>at</i> utility.</dd><dt><b>-t </b> <i>time_arg</i></dt><dd>Submit the job to be run at the time specified by the <i>time</i> option-argument, which the application shall ensure has theformat as specified by the <a href="../utilities/touch.html"><i>touch</i></a> <b>-t</b> <i>time</i> utility.</dd></dl></blockquote><h4><a name="tag_04_05_05"></a>OPERANDS</h4><blockquote><p>The following operands shall be supported:</p><dl compact><dt><i>at_job_id</i></dt><dd>The name reported by a previous invocation of the <i>at</i> utility at the time the job was scheduled.</dd><dt><i>timespec</i></dt><dd>Submit the job to be run at the date and time specified. All of the <i>timespec</i> operands are interpreted as if they wereseparated by <space>s and concatenated, and shall be parsed as described in the grammar at the end of this section. The dateand time shall be interpreted as being in the timezone of the user (as determined by the <i>TZ</i> variable), unless a timezonename appears as part of <i>time</i>, below. <p>In the POSIX locale, the following describes the three parts of the time specification string. All of the values from the<i>LC_TIME</i> categories in the POSIX locale shall be recognized in a case-insensitive manner.</p><dl compact><dt><i>time</i></dt><dd>The time can be specified as one, two, or four digits. One-digit and two-digit numbers shall be taken to be hours; four-digitnumbers to be hours and minutes. The time can alternatively be specified as two numbers separated by a colon, meaning<i>hour</i>:<i>minute</i>. An AM/PM indication (one of the values from the <b>am_pm</b> keywords in the <i>LC_TIME</i> localecategory) can follow the time; otherwise, a 24-hour clock time shall be understood. A timezone name can also follow to furtherqualify the time. The acceptable timezone names are implementation-defined, except that they shall be case-insensitive and thestring <b>utc</b> is supported to indicate the time is in Coordinated Universal Time. In the POSIX locale, the <i>time</i> fieldcan also be one of the following tokens: <dl compact><dt><b>midnight</b></dt><dd>Indicates the time 12:00 am (00:00).</dd><dt><b>noon</b></dt><dd>Indicates the time 12:00 pm.</dd><dt><b>now</b></dt><dd>Indicates the current day and time. Invoking <i>at</i> <<b>now</b>> shall submit an at-job for potentially immediateexecution (that is, subject only to unspecified scheduling delays).</dd></dl></dd><dt><i>date</i></dt><dd>An optional <i>date</i> can be specified as either a month name (one of the values from the <b>mon</b> or <b>abmon</b> keywordsin the <i>LC_TIME</i> locale category) followed by a day number (and possibly year number preceded by a comma), or a day of theweek (one of the values from the <b>day</b> or <b>abday</b> keywords in the <i>LC_TIME</i> locale category). In the POSIX locale,two special days shall be recognized: <dl compact><dt><b>today</b></dt><dd>Indicates the current day.</dd><dt><b>tomorrow</b></dt><dd>Indicates the day following the current day.</dd></dl><p>If no <i>date</i> is given, <b>today</b> shall be assumed if the given time is greater than the current time, and<b>tomorrow</b> shall be assumed if it is less. If the given month is less than the current month (and no year is given), next yearshall be assumed.</p></dd><dt><i>increment</i></dt><dd>The optional <i>increment</i> shall be a number preceded by a plus sign ( <tt>'+'</tt> ) 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 shall also beaccepted.) The keyword <b>next</b> shall be equivalent to an increment number of +1. For example, the following are equivalentcommands: <pre><tt>at 2pm + 1 weekat 2pm next week</tt></pre></dd></dl></dd></dl><p>The following grammar describes the precise format of <i>timespec</i> in the POSIX locale. The general conventions for thisstyle of grammar are described in <a href="xcu_chap01.html#tag_01_10"><i>Grammar Conventions</i></a> . This formal syntax shalltake precedence over the preceding text syntax description. The longest possible token or delimiter shall be recognized at a givenpoint. When used in a <i>timespec</i>, white space shall also delimit tokens.</p><pre><tt>%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].*/<br>%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].*/<br>%token minute/* A minute is a one or two-digit number whose value can be [0,9] or [00,59].*/<br>%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.*/<br>%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.*/<br>%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.*/<br>%token timezone_name/* The name of an optional timezone suffix to the time field, in an implementation-defined format.*/<br>%token month_name/* One of the values from the mon or abmon keywords in the LC_TIME locale category.*/<br>%token day_of_week/* One of the values from the day or abday keywords in the LC_TIME locale category.*/<br>%token am_pm/* One of the values from the am_pm keyword in the LC_TIME locale category.*/<br>%start timespec%%timespec : time | time date | time increment | time date increment | nowspec ;<br>nowspec : "now" | "now" increment ;<br>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" ;<br>date : month_name day_number | month_name day_number "," year_number | day_of_week | "today" | "tomorrow" ;<br>increment : "+" inc_number inc_period | "next" inc_period ;<br>inc_period : "minute" | "minutes" | "hour" | "hours" | "day" | "days" | "week" | "weeks" | "month" | "months" | "year" | "years" ;</tt></pre></blockquote><h4><a name="tag_04_05_06"></a>STDIN</h4><blockquote><p>The standard input shall be a text file consisting of commands acceptable to the shell command language described in <a href="xcu_chap02.html#tag_02"><i>Shell Command Language</i></a> . The standard input shall only be used if no <b>-f</b> <i>file</i>option is specified.</p></blockquote>⌨️ 快捷键说明
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