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| <h3 class="section">2.45 <code>system</code>—execute command string</h3> |
| |
| <p><a name="index-system-106"></a><a name="index-g_t_005fsystem_005fr-107"></a><strong>Synopsis</strong> |
| <pre class="example"> #include <stdlib.h> |
| int system(char *<var>s</var>); |
| |
| int _system_r(void *<var>reent</var>, char *<var>s</var>); |
| |
| </pre> |
| <p><strong>Description</strong><br> |
| |
| <p>Use <code>system</code> to pass a command string <code>*</code><var>s</var> to <code>/bin/sh</code> on |
| your system, and wait for it to finish executing. |
| |
| <p>Use “<code>system(NULL)</code>” to test whether your system has <code>/bin/sh</code> |
| available. |
| |
| <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> |
| <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>With a command argument, the result of <code>system</code> is the exit status |
| returned by <code>/bin/sh</code>. |
| |
| <p><br> |
| <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>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>Supporting OS subroutines required: <code>_exit</code>, <code>_execve</code>, <code>_fork_r</code>, |
| <code>_wait_r</code>. |
| |
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