ch05_08.htm

unix基础教程

By default, the current limits are shown or set; with <tt class="literal">-h</tt>, 
hard limits are used.  A hard limit 


imposes an absolute limit that can't
be exceeded.  Only a privileged user may raise it.
See also <b class="emphasis-bold"><a href="#unlimit">unlimit</a></b>.</p>
<h4 class="refsect2">Resource</h4><dl><dt><tt class="literal">cputime</tt></dt><dd>Maximum number of seconds the CPU can spend;
can be abbreviated as <tt class="literal">cpu</tt></p>
</dd>
<dt><tt class="literal">filesize</tt></dt><dd>Maximum size of any one file</p>
</dd>
<dt><tt class="literal">datasize</tt></dt><dd>Maximum size of data (including stack)</p>
</dd>
<dt><tt class="literal">stacksize</tt></dt><dd>Maximum size of stack</p>
</dd>
<dt><tt class="literal">coredumpsize</tt></dt><dd>Maximum size of a core dump file</p>
</dd>
</dl>

<h4 class="refsect2">Limit</h4><p>A number followed by an optional character (a unit specifier).</p>

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


<tr><td>For <tt class="literal">cputime</tt>:</td>
<td><em class="emphasis">n</em><tt class="literal">h</tt> (for
<em class="emphasis">n</em> hours),
<em class="emphasis">n</em><tt class="literal">m</tt> (for <em class="emphasis">n</em>
minutes), <em class="emphasis">mm</em><tt class="literal">:</tt><tt class="literal">ss</tt>
(minutes and seconds).</td></tr>

<tr><td>For others:</td>
<td><em class="emphasis">n</em><tt class="literal">k</tt> (for
<em class="emphasis">n</em> kilobytes, the default), <em class="emphasis">n</em><tt class="literal">m</tt> (for <em class="emphasis">n</em> megabytes).</td></tr>
</table><p>

</td></tr><tr><td valign="top"><a name="login">login</a></a></td><td><tt class="literal">login</tt> [<em class="replaceable"><tt>user</tt></em> | <tt class="literal">-p</tt> ]
<p>
<a name="IXT-5-123062" />Replace <em class="emphasis">user</em>'s login shell with <tt class="literal">/bin/login</tt>.
<tt class="literal">-p</tt> preserves environment variables.</p>
</td></tr><tr><td valign="top"><a name="logout">logout</a></a></td><td><tt class="literal">logout</tt>
<p>
<a name="IXT-5-123063" />Terminate the login shell.</p>
</td></tr><tr><td valign="top"><a name="nice">nice</a></a></td><td><tt class="literal">nice</tt> [<tt class="literal">&#177;</tt><em class="replaceable"><tt>n</em>] <em class="replaceable">command</tt></em>
<p>
<a name="IXT-5-123064" />Change the execution priority for <em class="emphasis">command</em>, or, if
none is given, change priority for the current shell.
(See also <b class="emphasis-bold"><a href="ch02_01.htm#nice">nice</a></b> in <a href="ch02_01.htm">Chapter 2</a>.)
The priority range is -20 to 20, with a default of 4.
The range is backwards from what you might expect:
-20 gives the highest priority
(fastest execution); 20 gives the lowest.</p>


<dl><dt><tt class="literal">+</tt><tt><em class="replaceable">n</em></tt></dt><dd>Add <em class="emphasis">n</em></tt> to the priority value (lower job priority).</p>
</dd>
<dt><tt class="literal">-</tt><tt><em class="replaceable">n</em></tt></dt><dd>Subtract <em class="emphasis">n</em></tt> from the priority value (raise job priority).
Privileged users only.</p>
</dd>
</dl>
</td></tr><tr><td valign="top"><a name="nohup">nohup</a></a></td><td><tt class="literal">nohup</tt> [<em class="replaceable"><tt>command</tt></em>]
<p>
<a name="IXT-5-123065" />&#8220;No hangup signals.&#8221;
Do not terminate <em class="emphasis">command</em> after terminal line is
closed (i.e., when you hang up from a phone or log out).  
Use without <em class="emphasis">command</em> in shell


scripts to keep script from
being terminated.
(See also <b class="emphasis-bold"><a href="ch02_01.htm#nohup">nohup</a></b> in <a href="ch02_01.htm">Chapter 2</a>.)</p>
</td></tr><tr><td valign="top"><a name="notify">notify</a></a></td><td><tt class="literal">notify</tt> [<em class="replaceable"><tt>jobID</tt></em>]
<p>
<a name="IXT-5-123066" />Report immediately when a background job finishes
(instead of waiting for you to exit a long editing session,
for example).  If no <em class="emphasis">jobID</em> is given, the current background
job is assumed.</p>
</td></tr><tr><td valign="top"><a name="onintr">onintr</a></a></td><td><tt class="literal">onintr</tt> <em class="replaceable"><tt>label</tt></em><br><tt class="literal">onintr -</tt><br><tt class="literal">onintr</tt>
<p>
<a name="IXT-5-123067" />&#8220;On interrupt.&#8221;  Used in shell scripts to handle interrupt signals
(similar to the Bourne shell's <tt class="literal">trap 2</tt> and <tt class="literal">trap "" 2</tt> commands).
The first form is like a <tt class="literal">goto</tt> <em class="emphasis">label</em>.  The script
branches to <em class="emphasis">label</em><tt class="literal">:</tt> if it catches an interrupt signal (e.g., <tt class="literal">CTRL-C</tt>).
The second form lets the script ignore interrupts.  This is useful
at the beginning of a script or before any code segment that needs
to run unhindered (e.g., when moving files).
The third form restores interrupt handling that was previously disabled
with <tt class="literal">onintr -</tt>.</p>
<h4 class="refsect2">Example</h4><blockquote><pre class="code">onintr cleanup     <i class="lineannotation">Go to &#8220;cleanup&#8221; on interrupt</i>
 .
 .                 <i class="lineannotation">Shell script commands</i>
 .
cleanup:           <i class="lineannotation">Label for interrupts</i>
  onintr -         <i class="lineannotation">Ignore additional interrupts</i>
  rm -f $tmpfiles  <i class="lineannotation">Remove any files created</i>
  exit 2           <i class="lineannotation">Exit with an error status</i></pre></blockquote>

</td></tr><tr><td valign="top"><a name="popd">popd</a></a></td><td><tt class="literal">popd</tt> [<tt class="literal">+</tt><em class="replaceable"><tt>n</tt></em>]
<p>
<a name="IXT-5-123068" />Remove


the current entry from the directory stack
or remove the <em class="emphasis">n</em>th entry from the stack.  The current
entry has number 0 and appears on the left.
See also <b class="emphasis-bold"><a href="#dirs">dirs</a></b> and 
<b class="emphasis-bold"><a href="#pushd">pushd</a></b>.
</p>
</td></tr>

<tr><td valign="top"><a name="pushd">pushd</a></a></td><td><p><tt class="literal">pushd</tt> <em class="replaceable"><tt>name</em></p><p><tt class="literal">pushd</tt> <tt class="literal">+</tt><em class="replaceable">n</tt></em></p><p><tt class="literal">pushd</tt></p>
<p>
<a name="IXT-5-123069" />The first form changes the working directory to <em class="emphasis">name</em> and adds it
to the directory stack.  The second form rotates the <em class="emphasis">n</em>th entry to the
beginning, making it the working directory.  (Entry numbers begin at 0.)
With no arguments, <tt class="literal">pushd</tt> switches the first two entries
and changes to the new current directory.  See also <b class="emphasis-bold"><a href="#dirs">dirs</a></b> and <b class="emphasis-bold"><a href="#popd">popd</a></b>.</a> 
<h4 class="refsect2">Examples</h4><blockquote><pre class="code">5% <tt class="userinput"><b>dirs</b></tt>
/home/bob /usr
6% <tt class="userinput"><b>pushd /etc</b></tt>             <i class="lineannotation">Add /etc to directory stack</i>
/etc /home/bob /usr
7% <tt class="userinput"><b>pushd +2</b></tt>               <i class="lineannotation">Switch to third directory</i>
/usr /etc /home/bob
8% <tt class="userinput"><b>pushd</b></tt>                  <i class="lineannotation">Switch top two directories</i>
/etc /usr /home/bob
9% <tt class="userinput"><b>popd</b></tt>                   <i class="lineannotation">Discard current entry; go to next</i>
/usr /home/bob</pre></blockquote>

</td></tr><tr><td valign="top"><a name="rehash">rehash</a></a></td><td><tt class="literal">rehash</tt>
<p>
<a name="IXT-5-123070" />Recompute the hash table for the <tt class="literal">path</tt> variable.  
Use <tt class="literal">rehash</tt> whenever a new command is created during the current session.
This allows the shell
to locate and execute the command.
(If the new command resides in a directory not listed in <tt class="literal">path</tt>,
add this directory to <tt class="literal">path</tt> before rehashing.)
See also <b class="emphasis-bold"><a href="#unhash">unhash</a></b>.</p>
</td></tr>

<tr><td valign="top"><a name="repeat">repeat</a></a></td><td><p><tt class="literal">repeat</tt> <em class="replaceable"><tt>n command</tt></em></p>
<p>
<a name="IXT-5-123071" />Execute <em class="emphasis">n</em> instances of <em class="emphasis">command</em>.</p>
<h4 class="refsect2">Examples</h4><p>Generate a test file for a program by saving
25 copies of <tt class="literal">/usr/dict/words</tt> in a file:</p>
<blockquote><pre class="code">% <tt class="userinput"><b>repeat 25 cat /usr/dict/words &gt; test_file</b></tt></pre></blockquote>
<p>Read 10 lines from the terminal and store in <tt class="literal">item_list</tt>:</p>
<blockquote><pre class="code">% <tt class="userinput"><b>repeat 10 line &gt; item_list</b></tt></pre></blockquote>
<p>Append


50 boilerplate files to <tt class="literal">report</tt>:</p>
<blockquote><pre class="code">% <tt class="userinput"><b>repeat 50 cat template &gt;&gt; report</b></tt></pre></blockquote>

</td></tr><tr><td valign="top"><a name="set">set</a></a></td><td><tt class="literal">set</tt> <em class="replaceable"><tt>variable</em> <tt class="literal">=</tt> <em class="replaceable">value</em><br><tt class="literal">set</tt> <em class="replaceable">variable</em><tt class="literal">[</tt><em class="replaceable">n</em><tt class="literal">] =</tt> <em class="replaceable">value</tt></em><br><tt class="literal">set</tt>
<p>
<a name="IXT-5-123072" />Set <em class="emphasis">variable</em> to <em class="emphasis">value</em>, or, if multiple values are specified, set the
variable to the list of words in the value list.  If an index <em class="emphasis">n</em>
is specified, set the <em class="emphasis">n</em>th word in the variable to <em class="emphasis">value</em>.
(The variable must already contain at least that number of words.)
With no arguments, display the names and values of all set variables.
See also <a href="ch05_03.htm#unut-ch-5-sect-3.3">Section 5.3.3</a>  earlier in this chapter.</p>
<h4 class="refsect2">Examples</h4><blockquote><pre class="code">% <tt class="userinput"><b>set list=(yes no maybe)</b></tt>           <i class="lineannotation">Assign a word list</i>
% <tt class="userinput"><b>set list[3]=maybe</b></tt>                 <i class="lineannotation">Assign an item in existing word list</i>
% <tt class="userinput"><b>set quote="Make my day"</b></tt>           <i class="lineannotation">Assign a variable</i>
% <tt class="userinput"><b>set x=5 y=10 history=100</b></tt>          <i class="lineannotation">Assign several variables</i>
% <tt class="userinput"><b>set blank</b></tt>                         <i class="lineannotation">Assign a null value to blank</i> </pre></blockquote>

</td></tr><tr><td valign="top"><a name="setenv">setenv</a></a></td><td><tt class="literal">setenv</tt> [<em class="replaceable"><tt>name</em> [<em class="replaceable">value</tt></em>]]
<p>
<a name="IXT-5-123073" />Assign a <em class="emphasis">value</em> to an environment variable <em class="emphasis">name</em>.
By convention, <em class="emphasis">name</em> should be uppercase.
<em class="emphasis">value</em> can be a single word or a quoted string.
If no <em class="emphasis">value</em> is given, the null value is assigned.
With no arguments, display the names and values of all 
environment variables.  <tt class="literal">setenv</tt> is not necessary for the
USER, TERM, and PATH variables
because they are automatically exported
from <tt class="literal">user</tt>, <tt class="literal">term</tt>, and <tt class="literal">path</tt>.
See also <a href="ch05_03.htm#unut-ch-5-sect-3.5">Section 5.3.5</a>.</p>
</td></tr><tr><td valign="top"><a name="shift">shift</a></a></td><td><tt class="literal">shift</tt> [<em class="replaceable"><tt>variable</tt></em>]