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<a name="system_002d_002d_002dexecute-command-string"></a>
<h3 class="section">2.48 <code>system</code>&mdash;execute command string</h3>
<a name="index-system"></a>
<a name="index-_005fsystem_005fr"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;stdlib.h&gt;
int system(char *<var>s</var>);

int _system_r(void *<var>reent</var>, char *<var>s</var>);

</pre></div>
<p><strong>Description</strong><br>
</p>
<p>Use <code>system</code> to pass a command string <code>*<var>s</var></code> to <code>/bin/sh</code> on
your system, and wait for it to finish executing.
</p>
<p>Use &ldquo;<code>system(NULL)</code>&rdquo; to test whether your system has <code>/bin/sh</code>
available.
</p>
<p>The alternate function <code>_system_r</code> is a reentrant version.  The
extra argument <var>reent</var> is a pointer to a reentrancy structure.
</p>
<br>
<p><strong>Returns</strong><br>
<code>system(NULL)</code> returns a non-zero value if <code>/bin/sh</code> is available, and
<code>0</code> if it is not.
</p>
<p>With a command argument, the result of <code>system</code> is the exit status
returned by <code>/bin/sh</code>.
</p>
<br>
<p><strong>Portability</strong><br>
ANSI C requires <code>system</code>, but leaves the nature and effects of a
command processor undefined.  ANSI C does, however, specify that
<code>system(NULL)</code> return zero or nonzero to report on the existence of
a command processor.
</p>
<p>POSIX.2 requires <code>system</code>, and requires that it invoke a <code>sh</code>.
Where <code>sh</code> is found is left unspecified.
</p>
<p>Supporting OS subroutines required: <code>_exit</code>, <code>_execve</code>, <code>_fork_r</code>,
<code>_wait_r</code>.
</p>
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