157 lines
6.7 KiB
HTML
157 lines
6.7 KiB
HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>setenv</title>
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<basefont size="3"> <a name="setenv"></a> <a name="tag_03_647"></a><!-- setenv -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_647_01"></a>NAME</h4>
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<blockquote>setenv - add or change environment variable</blockquote>
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<h4><a name="tag_03_647_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/stdlib.h.html">stdlib.h</a>><br>
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<br>
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int setenv(const char *</tt><i>envname</i><tt>, const char *</tt><i>envval</i><tt>, int</tt> <i>overwrite</i><tt>); <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_647_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>setenv</i>() function shall update or add a variable in the environment of the calling process. The <i>envname</i>
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argument points to a string containing the name of an environment variable to be added or altered. The environment variable shall
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be set to the value to which <i>envval</i> points. The function shall fail if <i>envname</i> points to a string which contains an
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<tt>'='</tt> character. If the environment variable named by <i>envname</i> already exists and the value of <i>overwrite</i> is
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non-zero, the function shall return success and the environment shall be updated. If the environment variable named by
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<i>envname</i> already exists and the value of <i>overwrite</i> is zero, the function shall return success and the environment
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shall remain unchanged.</p>
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<p>If the application modifies <i>environ</i> or the pointers to which it points, the behavior of <i>setenv</i>() is undefined. The
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<i>setenv</i>() function shall update the list of pointers to which <i>environ</i> points.</p>
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<p>The strings described by <i>envname</i> and <i>envval</i> are copied by this function.</p>
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<p>The <i>setenv</i>() function need not be reentrant. A function that is not required to be reentrant is not required to be
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thread-safe.</p>
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</blockquote>
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<h4><a name="tag_03_647_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, zero shall be returned. Otherwise, -1 shall be returned, <i>errno</i> set to indicate the error, and
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the environment shall be unchanged.</p>
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</blockquote>
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<h4><a name="tag_03_647_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>setenv</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The <i>name</i> argument is a null pointer, points to an empty string, or points to a string containing an <tt>'='</tt>
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character.</dd>
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<dt>[ENOMEM]</dt>
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<dd>Insufficient memory was available to add a variable or its value to the environment.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_647_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_647_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_647_08"></a>RATIONALE</h4>
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<blockquote>
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<p>Unanticipated results may occur if <i>setenv</i>() changes the external variable <i>environ</i>. In particular, if the optional
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<i>envp</i> argument to <i>main</i>() is present, it is not changed, and thus may point to an obsolete copy of the environment (as
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may any other copy of <i>environ</i>). However, other than the aforementioned restriction, the developers of
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IEEE Std 1003.1-2001 intended that the traditional method of walking through the environment by way of the <i>environ</i>
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pointer must be supported.</p>
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<p>It was decided that <i>setenv</i>() should be required by this revision because it addresses a piece of missing functionality,
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and does not impose a significant burden on the implementor.</p>
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<p>There was considerable debate as to whether the System V <a href="../functions/putenv.html"><i>putenv</i>()</a> function or the
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BSD <i>setenv</i>() function should be required as a mandatory function. The <i>setenv</i>() function was chosen because it
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permitted the implementation of the <a href="../functions/unsetenv.html"><i>unsetenv</i>()</a> function to delete environmental
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variables, without specifying an additional interface. The <a href="../functions/putenv.html"><i>putenv</i>()</a> function is
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available as an XSI extension.</p>
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<p>The standard developers considered requiring that <i>setenv</i>() indicate an error when a call to it would result in exceeding
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{ARG_MAX}. The requirement was rejected since the condition might be temporary, with the application eventually reducing the
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environment size. The ultimate success or failure depends on the size at the time of a call to <i><a href=
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"../functions/exec.html">exec</a></i>, which returns an indication of this error condition.</p>
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</blockquote>
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<h4><a name="tag_03_647_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_647_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="getenv.html"><i>getenv</i>()</a> , <a href="unsetenv.html"><i>unsetenv</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/stdlib.h.html"><i><stdlib.h></i></a>, <a href=
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"../basedefs/sys/types.h.html"><i><sys/types.h></i></a>, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_647_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 6. Derived from the IEEE P1003.1a draft standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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