getconf.html

posix标准英文,html格式

<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
Determine the location of message catalogs for the processing of <i>LC_MESSAGES .</i> <img src="../images/opt-end.gif" alt=
"[Option End]" border="0"></dd>
</dl>
</blockquote>

<h4><a name="tag_04_61_09"></a>ASYNCHRONOUS EVENTS</h4>

<blockquote>
<p>Default.</p>
</blockquote>

<h4><a name="tag_04_61_10"></a>STDOUT</h4>

<blockquote>
<p>If the specified variable is defined on the system and its value is described to be available from the <a href=
"../functions/confstr.html"><i>confstr</i>()</a> function defined in the System Interfaces volume of
IEEE&nbsp;Std&nbsp;1003.1-2001, its value shall be written in the following format:</p>

<pre>
<tt>"%s\n", &lt;</tt><i>value</i><tt>&gt;
</tt>
</pre>

<p>Otherwise, if the specified variable is defined on the system, its value shall be written in the following format:</p>

<pre>
<tt>"%d\n", &lt;</tt><i>value</i><tt>&gt;
</tt>
</pre>

<p>If the specified variable is valid, but is undefined on the system, <i>getconf</i> shall write using the following format:</p>

<pre>
<tt>"undefined\n"
</tt>
</pre>

<p>If the variable name is invalid or an error occurs, nothing shall be written to standard output.</p>
</blockquote>

<h4><a name="tag_04_61_11"></a>STDERR</h4>

<blockquote>
<p>The standard error shall be used only for diagnostic messages.</p>
</blockquote>

<h4><a name="tag_04_61_12"></a>OUTPUT FILES</h4>

<blockquote>
<p>None.</p>
</blockquote>

<h4><a name="tag_04_61_13"></a>EXTENDED DESCRIPTION</h4>

<blockquote>
<p>None.</p>
</blockquote>

<h4><a name="tag_04_61_14"></a>EXIT STATUS</h4>

<blockquote>
<p>The following exit values shall be returned:</p>

<dl compact>
<dt>&nbsp;0</dt>

<dd>The specified variable is valid and information about its current state was written successfully.</dd>

<dt>&gt;0</dt>

<dd>An error occurred.</dd>
</dl>
</blockquote>

<h4><a name="tag_04_61_15"></a>CONSEQUENCES OF ERRORS</h4>

<blockquote>
<p>Default.</p>
</blockquote>

<hr>
<div class="box"><em>The following sections are informative.</em></div>

<h4><a name="tag_04_61_16"></a>APPLICATION USAGE</h4>

<blockquote>
<p>None.</p>
</blockquote>

<h4><a name="tag_04_61_17"></a>EXAMPLES</h4>

<blockquote>
<p>The following example illustrates the value of {NGROUPS_MAX}:</p>

<pre>
<tt>getconf NGROUPS_MAX
</tt>
</pre>

<p>The following example illustrates the value of {NAME_MAX} for a specific directory:</p>

<pre>
<tt>getconf NAME_MAX /usr
</tt>
</pre>

<p>The following example shows how to deal more carefully with results that might be unspecified:</p>

<pre>
<tt>if value=$(getconf PATH_MAX /usr); then
    if [ "$value" = "undefined" ]; then
        echo PATH_MAX in /usr is infinite.
    else
        echo PATH_MAX in /usr is $value.
    fi
else
    echo Error in getconf.
fi
</tt>
</pre>

<p>Note that:</p>

<pre>
<tt>sysconf(_SC_POSIX_C_BIND);
</tt>
</pre>

<p>and:</p>

<pre>
<tt>system("getconf POSIX2_C_BIND");
</tt>
</pre>

<p>in a C program could give different answers. The <a href="../functions/sysconf.html"><i>sysconf</i>()</a> call supplies a value
that corresponds to the conditions when the program was either compiled or executed, depending on the implementation; the <a href=
"../functions/system.html"><i>system</i>()</a> call to <i>getconf</i> always supplies a value corresponding to conditions when the
program is executed.</p>
</blockquote>

<h4><a name="tag_04_61_18"></a>RATIONALE</h4>

<blockquote>
<p>The original need for this utility, and for the <a href="../functions/confstr.html"><i>confstr</i>()</a> function, was to
provide a way of finding the configuration-defined default value for the <i>PATH</i> environment variable. Since <i>PATH</i> can be
modified by the user to include directories that could contain utilities replacing the standard utilities, shell scripts need a way
to determine the system-supplied <i>PATH</i> environment variable value that contains the correct search path for the standard
utilities. It was later suggested that access to the other variables described in this volume of IEEE&nbsp;Std&nbsp;1003.1-2001
could also be useful to applications.</p>

<p>This functionality of <i>getconf</i> would not be adequately subsumed by another command such as:</p>

<pre>
<tt>grep</tt> <i>var</i> <tt>/etc/conf
</tt>
</pre>

<p>because such a strategy would provide correct values for neither those variables that can vary at runtime, nor those that can
vary depending on the path.</p>

<p>Early proposal versions of <i>getconf</i> specified exit status 1 when the specified variable was valid, but not defined on the
system. The output string <tt>"undefined"</tt> is now used to specify this case with exit code 0 because so many things depend on
an exit code of zero when an invoked utility is successful.</p>
</blockquote>

<h4><a name="tag_04_61_19"></a>FUTURE DIRECTIONS</h4>

<blockquote>
<p>None.</p>
</blockquote>

<h4><a name="tag_04_61_20"></a>SEE ALSO</h4>

<blockquote>
<p><a href="c99.html"><i>c99</i></a>, the Base Definitions volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../basedefs/limits.h.html"><i>&lt;limits.h&gt;</i></a>, the System Interfaces volume of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href=
"../functions/confstr.html"><i>confstr</i>()</a>, <a href="../functions/pathconf.html"><i>pathconf</i>()</a>, <a href=
"../functions/sysconf.html"><i>sysconf</i>()</a>, <a href="../functions/system.html"><i>system</i>()</a></p>
</blockquote>

<h4><a name="tag_04_61_21"></a>CHANGE HISTORY</h4>

<blockquote>
<p>First released in Issue 4.</p>
</blockquote>

<h4><a name="tag_04_61_22"></a>Issue 5</h4>

<blockquote>
<p>In the OPERANDS section:</p>

<ul>
<li>
<p>{NL_MAX} is changed to {NL_NMAX}.</p>
</li>

<li>
<p>Entries beginning NL_ are deleted from the list of standard configuration variables.</p>
</li>

<li>
<p>The list of variables previously marked UX is merged with the list marked EX.</p>
</li>

<li>
<p>Operands are added to support new Option Groups.</p>
</li>

<li>
<p>Operands are added so that <i>getconf</i> can determine supported programming environments.</p>
</li>
</ul>
</blockquote>

<h4><a name="tag_04_61_23"></a>Issue 6</h4>

<blockquote>
<p>The Open Group Corrigendum U029/4 is applied, correcting the example command in the last paragraph of the OPTIONS section.</p>

<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>

<ul>
<li>
<p>Operands are added to determine supported programming environments.</p>
</li>
</ul>

<p>This reference page is updated for alignment with the ISO/IEC&nbsp;9899:1999 standard. Specifically, new macros for <a href=
"../utilities/c99.html"><i>c99</i></a> programming environments are introduced.</p>

<p>XSI marked <i>system_var</i> (XBS5_*) values are marked LEGACY.</p>

<p>IEEE&nbsp;Std 1003.1-2001/Cor&nbsp;1-2002, item XCU/TC1/D6/27 is applied, correcting the descriptions of <i>path_var</i> and
<i>system_var</i> in the OPERANDS section.</p>
</blockquote>

<div class="box"><em>End of informative text.</em></div>

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