ch02_01.htm

unix基础教程

as a numeric hour (with optional minutes and modifiers)
or as a keyword.  <em class="emphasis">date</em></tt> can be formed either
as a month and date, as a day of the week, or as a special keyword.
<em class="emphasis">increment</em></tt> is a positive integer followed by a keyword.
See the following lists for details.</p>
<h4 class="refsect2">Options1</h4><dl><dt><tt class="literal">-c</tt></dt><dd>Use the C shell to execute the job.
Solaris only.</p>
</dd>
<dt><tt class="literal">-f</tt> <tt><em class="replaceable">file</em></tt></dt><dd>Execute commands listed in <em class="emphasis">file</em></tt>.</p>
</dd>
<dt><tt class="literal">-k</tt></dt><dd>Use the Korn shell to execute the job.
Solaris only.</p>
</dd>
<dt><tt class="literal">-m</tt></dt><dd>Send mail to user after job is completed.</p>
</dd>
<dt><tt class="literal">-q</tt> <tt><em class="replaceable">queuename</em></tt></dt><dd>Schedule the job in <em class="emphasis">queuename</em></tt>.
Values for <em class="emphasis">queuename</em> are the lowercase letters
<tt class="literal">a</tt> through <tt class="literal">z</tt>.
Queue <tt class="literal">a</tt> is the default queue for <tt class="literal">at</tt> jobs.
Queue <tt class="literal">b</tt> is the queue for <tt class="literal">batch</tt> jobs.
Queue <tt class="literal">c</tt> is the queue for <tt class="literal">cron</tt> jobs.
Solaris only.</p>
</dd>
<dt><tt class="literal">-s</tt></dt><dd>Use the Bourne shell to execute the job.
Solaris only.</p>
</dd>
<dt><tt class="literal">-t</tt> <tt><em class="replaceable">time</em></tt></dt><dd>Run the job at <em class="emphasis">time</em></tt>, which is in the same format as
allowed by <tt class="literal">touch</tt>.
Solaris only.</p>
</dd>
</dl>

<h4 class="refsect2">Options2</h4><dl><dt><tt class="literal">-l</tt></dt><dd>Report all jobs that are scheduled for the invoking user or,
if <em class="emphasis">jobs</em></tt> are specified, report only for those.
See also <b class="emphasis-bold"><a href="#atq">atq</a></b>.</p>
</dd>
<dt><tt class="literal">-r</tt></dt><dd>Remove specified <em class="emphasis">jobs</em></tt> that were previously scheduled.  To remove a job,
you must be a privileged user or the owner of the job.  Use <tt class="literal">-l</tt> first
to see the list of scheduled jobs.  See also <b class="emphasis-bold"><a href="#atrm">atrm</a></b>.</p>
</dd>
</dl>

<h4 class="refsect2">Time</h4><dl><dt><i><tt><em class="replaceable"><tt>hh</em></tt><tt class="literal">:</tt><tt><em class="replaceable">mm</em></tt> [<tt><em class="replaceable">modifiers</tt></em></tt>]</i></dt><dd>Hours can have one or two digits (a 24-hour clock is assumed by default);
optional minutes can be given as one or two digits;
the colon can be omitted if the format is <em class="emphasis">h</em></tt>, <em class="emphasis">hh</em></tt>, or <em class="emphasis">hhmm</em></tt>;
e.g., valid times are 5, 5:30, 0530, 19:45.
If modifier <tt class="literal">am</tt> or <tt class="literal">pm</tt> is added, <em class="emphasis">time</em></tt> is based on
a 12-hour clock.  If the keyword <tt class="literal">zulu</tt>
is added, times correspond to Greenwich Mean Time (UTC).</p>
</dd>
<dt><tt class="literal">midnight </tt>| <tt class="literal">noon </tt>| <tt class="literal">now</tt></dt><dd>Use any one of these keywords in place of a numeric time.
<tt class="literal">now</tt> must be followed by an <em class="emphasis">increment</em>.</p>
</dd>
</dl>

<h4 class="refsect2">Date</h4><dl><dt><i><tt><em class="replaceable"><tt>month num</em></tt>[<tt class="literal">,</tt> <tt><em class="replaceable">year</em></tt>]</i></dt><dd><em class="emphasis">month</em></tt> is one of the 12 months, spelled out or abbreviated to
their first three letters; <em class="emphasis">num</tt></em></tt> is the calendar day of the month;
<em class="emphasis">year</em></tt> is the four-digit year.  If the given <em class="emphasis">month</em></tt> occurs before
the current month, <tt class="literal">at</tt> schedules that month next year.</p>
</dd>
<dt><i><tt><em class="replaceable"><tt>day</tt></em></tt></i></dt><dd>One of the seven days of the week, spelled out or abbreviated to their
first three letters.</p>
</dd>
<dt><tt class="literal">today </tt>| <tt class="literal">tomorrow</tt></dt><dd>Indicate the current day or the next day.  If <em class="emphasis">date</em></tt> is omitted,
<tt class="literal">at</tt> schedules <tt class="literal">today</tt> when the specified <em class="emphasis">time</em></tt> occurs
later than the current time; otherwise, <tt class="literal">at</tt> schedules <tt class="literal">tomorrow</tt>.</p>
</dd>
</dl>

<h4 class="refsect2">Increment</h4><p>Supply a numeric increment if you want to specify an execution time or day
<em class="emphasis">relative</em></tt> to the current time.  The number should precede any of
the keywords <tt class="literal">minute</tt>, <tt class="literal">hour</tt>, <tt class="literal">day</tt>,
<tt class="literal">week</tt>, <tt class="literal">month</tt>, or
<tt class="literal">year</tt> (or their plural forms).
The keyword <tt class="literal">next</tt> can be used
as a synonym of <tt class="literal">+ 1</tt>.</p>

<h4 class="refsect2">Examples</h4><p>Note that the first two commands are equivalent:</p>
<blockquote><pre class="code"><tt class="userinput"><b>at 1945 pm December 9
at 7:45pm Dec 9
at 3 am Saturday
at now + 5 hours
at noon next day</b></tt></pre></blockquote>

</td></tr><tr><td valign="top"><a name="atq">atq</a></a></td><td><tt class="literal">atq</tt> [<tt><em class="replaceable"><tt>options</em></tt>] [<tt><em class="replaceable">users</tt></em></tt>]
<p>
<a name="IXT-2-121822" />
<a name="IXT-2-121823" />List jobs created by the <tt class="literal">at</tt> command that are still in the queue.
Normally, jobs are sorted by the order in which they execute.
Specify the <em class="emphasis">users</em></tt> whose jobs you want to check.
If no <em class="emphasis">users</em></tt> are specified, the default is to display all jobs
if you're a privileged user; otherwise, only your jobs are displayed.</p>
<h4 class="refsect2">Options</h4><dl><dt><tt class="literal">-c</tt></dt><dd>Sort the queue according to the time the <tt class="literal">at</tt> command was given.</p>
</dd>
<dt><tt class="literal">-n</tt></dt><dd>Print only the total number of jobs in queue.</p>
</dd>
</dl>

</td></tr><tr><td valign="top"><a name="atrm">atrm</a></a></td><td><tt class="literal">atrm</tt> [<tt><em class="replaceable"><tt>options</em></tt>] [<tt><em class="replaceable">users </em></tt>| <tt><em class="replaceable">jobIDs</tt></em></tt>]
<p>
<a name="IXT-2-121824" />
<a name="IXT-2-121825" />Remove jobs queued with <tt class="literal">at</tt> that match the specified <em class="emphasis">jobIDs</em></tt>.
A privileged user may also specify the <em class="emphasis">users</em></tt> whose jobs are to be
removed.</p>
<h4 class="refsect2">Options</h4><dl><dt><tt class="literal">-a</tt></dt><dd>Remove all jobs belonging to the current user.
(A privileged user can remove <em class="emphasis">all</em> jobs.)</p>
</dd>
<dt><tt class="literal">-f</tt></dt><dd>Remove jobs unconditionally,
suppressing all information regarding removal.</p>
</dd>
<dt><tt class="literal">-i</tt></dt><dd>Prompt for <tt class="literal">y</tt> (remove the job) or <tt class="literal">n</tt> (do not remove).</p>
</dd>
</dl>

</td></tr><tr><td valign="top"><a name="awk">awk</a></a></td><td><tt class="literal">awk</tt> [<em class="replaceable"><tt>options</em>] [<em class="replaceable">program</em>] [<em class="replaceable">var</em><tt class="literal">=</tt><em class="replaceable">value</em> ...] [<em class="replaceable">files</tt></em>]
<p>
<a name="IXT-2-121826" />
<a name="IXT-2-121827" />
<a name="IXT-2-121828" />
<a name="IXT-2-121829" />Use the pattern-matching <em class="emphasis">program</em> to process the specified <em class="emphasis">files</em>.
<tt class="literal">awk</tt> has been replaced by <tt class="literal">nawk</tt> (there's also a GNU version called
<tt class="literal">gawk</tt>).
<em class="emphasis">program</em> instructions have the general form:</p>
<blockquote><pre class="code"><em class="replaceable"><tt>pattern</em> { <em class="replaceable">procedure</tt></em> }</pre></blockquote>
<p><em class="emphasis">pattern</em> and <em class="emphasis">procedure</em> are optional.
When specified on the command line, <em class="emphasis">program</em> must be
enclosed in single quotes to prevent the shell from interpreting
its special symbols.
Any variables specified in <em class="emphasis">program</em> can be assigned an
initial value by using command-line arguments of the form <em class="replaceable"><tt>var</em><tt class="literal">=</tt><em class="replaceable">value</tt></em>.
See <a href="ch11_01.htm">Chapter 11</a>,
for more information (including examples) on <tt class="literal">awk</tt>.</p>
<h4 class="refsect2">Options</h4><dl><dt><tt class="literal">-f</tt>&#160;<tt><em class="replaceable">file</em></tt></dt><dd>Use program instructions contained in <em class="emphasis">file</em></tt>, instead
of specifying <em class="emphasis">program</em></tt> on the command line.</p>
</dd>
<dt><tt class="literal">-F</tt><tt><em class="replaceable">c</em></tt></dt><dd>Treat input <em class="emphasis">file</em></tt> as fields separated by character
<em class="emphasis">c</em>.
By default, input fields are separated by runs of spaces and/or tabs.</p>
</dd>
</dl>

</td></tr><tr><td valign="top"><a name="banner">banner</a></a></td><td><tt class="literal">banner</tt> <em class="replaceable"><tt>characters</tt></em>
<p>
<a name="IXT-2-121830" />
<a name="IXT-2-121831" />Print <em class="emphasis">characters</em> as a poster on the standard output.
Each word supplied must contain ten characters or less.</p>
</td></tr><tr><td valign="top"><a name="basename">basename</a></a></td><td><tt class="literal">basename</tt> <em class="replaceable"><tt>pathname</em> [<em class="replaceable">suffix</tt></em>]
<p>
<a name="IXT-2-121832" />
<a name="IXT-2-121833" />
<a name="IXT-2-121834" />Given a <em class="emphasis">pathname</em>, strip the path prefix and
leave just the filename, which is printed on standard output.
If specified, a filename <em class="emphasis">suffix</em> (e.g., <tt class="literal">.c</tt>)
is removed also.  <tt class="literal">basename</tt> is typically invoked via
command substitution (<tt class="literal">&#8216;</tt>...<tt class="literal">&#8216;</tt>) to
generate a filename.  See also <b class="emphasis-bold"><a href="#dirname">dirname</a></b>.</p>
<p>The Solaris version of <tt class="literal">basename</tt> allows the suffix to be
a pattern of the form accepted by <tt class="literal">expr</tt>.
See the entry for <b class="emphasis-bold"><a href="#expr">expr</a></b> for more details.</p>
<h4 class="refsect2">Example</h4><p>Given the following fragment from a Bourne shell script:</p>
<blockquote><pre class="code">ofile=output_file
myname="`basename $0`"
echo "$myname: QUITTING: can't open $ofile" 1&gt;&amp;2
exit 1</pre></blockquote>
<p>If the script is called <tt class="literal">do_it</tt>, the following message would
be printed on standard error:</p>
<blockquote><pre class="code">do_it: QUITTING: can't open output_file</pre></blockquote>



</td></tr><tr><td valign="top"><a name="batch">batch</a></a></td><td><tt class="literal">batch</tt>
<p>
<a name="IXT-2-121835" />
<a name="IXT-2-121836" />Execute commands entered on standard input.  End with <em class="emphasis">EOF</em>.
Unlike <tt class="literal">at</tt>, which executes commands at a specific time,
<tt class="literal">batch</tt> executes commands one after another (waiting for each one
to complete).  This avoids the potentially high system load caused by running
several background jobs at once.  See also <b class="emphasis-bold"><a href="#at">at</a></b>.</p>
<p><tt class="literal">batch</tt> is equivalent to <tt class="literal">at -q b -m now</tt>.</p>
<h4 class="refsect2">Example</h4><blockquote><pre class="code">$ <tt class="userinput"><b>batch</b></tt>
<tt class="userinput"><b>sort</b></tt> <em class="replaceable"><tt>in</em> <tt class="userinput"><b>&gt;</b></tt> <em class="replaceable">out</tt></em>
<tt class="userinput"><b>troff -ms</b></tt> <em class="replaceable"><tt>bigfile</em> <tt class="userinput"><b>&gt;</b></tt> <em class="replaceable">bigfile.ps</tt></em>
<i class="lineannotation">EOF</i></pre></blockquote>

</td></tr><tr><td valign="top"><a name="bc">bc</a></a></td><td><tt class="literal">bc</tt> [<em class="replaceable"><tt>options</em>] [<em class="replaceable">files</tt></em>]
<p>
<a name="IXT-2-121837" />
<a name="IXT-2-121838" />Interactively perform arbitrary-precision arithmetic or convert numbers
from one base to another.  Input can be taken from
<em class="emphasis">files</em> or read from the standard input.  To exit, type
<tt class="literal">quit</tt> or <em class="emphasis">EOF</em>.</p>
<h4 class="refsect2">Options</h4><dl><dt><tt class="literal">-c</tt></dt><dd>Do not invoke <tt class="literal">dc</tt>; compile only.
(Since <tt class="literal">bc</tt> is a preprocessor for <tt class="literal">dc</tt>,
<tt class="literal">bc</tt> normally invokes <tt class="literal">dc</tt>.)</p>
</dd>
<dt><tt class="literal">-l</tt></dt><dd>Make available functions from the math library.</p>
</dd>
</dl>
<p><tt class="literal">bc</tt> is a language (and compiler) whose syntax resembles that of C.
<tt class="literal">bc</tt> consists of identifiers, keywords, and symbols, which
are briefly described here.  Examples follow at the end.</p>

<h4 class="refsect2">Identifiers</h4><p>An identifier is a single character, consisting of the lowercase
letters a&#8211;z.
Identifiers are used as names for variables, arrays, and functions.
Within the same program you may name a variable, an array,
and a function using the same letter.  The following identifiers would
not conflict:</p>

<table border="1" cellpadding="3">

<tr><td><tt class="literal">x</tt></td><td><p>Variable <tt class="literal">x</tt>.</p>
</td></tr>
<tr><td><tt class="literal">x[</tt><em class="replaceable"><tt>i</em><tt class="literal">]</tt></td><td><p>Element <em class="emphasis">i</tt></em> of array <tt class="literal">x</tt>.
<em class="emphasis">i</em> can range from 0 to 2047
and can also be an expression.</p>
</td></tr>
<tr><td><tt class="literal">x(y,z)</tt></td><td><p>Call function <tt class="literal">x</tt> with parameters <tt class="literal">y</tt> and <tt class="literal">z</tt>.</p>
</td></tr>