Linux下查看控制环境变量的方法

让一齐随风 發表於 2023-9-29 00:00:00

<p>
<strong>查看环境变量</strong></p>
<p>
查看某一环境变量：比如我们需要查看HOME这个环境变量，我们可以在shell下直接输入echo $HOME，我们可以把所有的环境变量和环境变量的值都打印出来</p>
<p>
<strong>打印环境变量</strong></p>
<p>
libc中定义的全局变量environ指向环境变量表,environ没有包含在任何头文件中,所以在使用时要用extern声明。</p>
<p>
下面提供了一个程序打印环境变量</p>
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<code class="cpp preprocessor">#include<stdio.h></code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">main()</code>
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<code class="cpp spaces"> </code><code class="cpp plain">{</code>
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<code class="cpp spaces">   </code><code class="cpp comments">//libc中定义的全局变量environ指向环境变量表,environ没有包含在任何头⽂文件中,所以</code>
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<code class="cpp spaces">   </code><code class="cpp comments">//在使⽤用时要⽤用extern声明。</code>
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<code class="cpp spaces">   </code><code class="cpp keyword bold">extern</code> <code class="cpp color1 bold">char</code><code class="cpp plain">** environ;</code>
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<code class="cpp spaces"> </code><code class="cpp comments">// while(environ)</code>
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<code class="cpp spaces"> </code><code class="cpp comments">// {</code>
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<code class="cpp spaces"> </code><code class="cpp comments">//   printf("%s\n",*environ++);</code>
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<code class="cpp spaces"> </code><code class="cpp comments">// }</code>
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<code class="cpp spaces"> </code><code class="cpp comments">// printf("hah");</code>
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<code class="cpp spaces">   </code><code class="cpp color1 bold">int</code> <code class="cpp plain">i = 0;</code>
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<code class="cpp spaces">   </code><code class="cpp keyword bold">for</code><code class="cpp plain">(i = 0;environ!=NULL;i++)</code>
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<code class="cpp spaces">   </code><code class="cpp plain">{</code>
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<code class="cpp spaces">     </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"%s\n"</code><code class="cpp plain">,environ);</code>
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<code class="cpp spaces">   </code><code class="cpp plain">}</code>
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<code class="cpp spaces">   </code><code class="cpp keyword bold">return</code> <code class="cpp plain">0;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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控制环境变量接口<code>getenv</code>，<code>setenv</code>，<code>unsetenv</code></p>
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<strong>getenv()函数</strong></p>
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<code class="cpp preprocessor">#include <stdlib.h></code>
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<code class="cpp color1 bold">char</code> <code class="cpp plain">*</code><code class="cpp functions bold">getenv</code><code class="cpp plain">(</code><code class="cpp keyword bold">const</code> <code class="cpp color1 bold">char</code> <code class="cpp plain">*name);</code>
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getenv()功能的搜索环境列表找到环境变量名称，并返回一个指向相应值串的指针。如果没有找到则返回NULL</p>
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<strong>setenv()函数和unsetenv</strong></p>
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<code class="cpp preprocessor">#include <stdlib.h></code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">setenv(</code><code class="cpp keyword bold">const</code> <code class="cpp color1 bold">char</code> <code class="cpp plain">*name, </code><code class="cpp keyword bold">const</code> <code class="cpp color1 bold">char</code> <code class="cpp plain">*value, </code><code class="cpp color1 bold">int</code> <code class="cpp plain">overwrite);</code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">unsetenv(</code><code class="cpp keyword bold">const</code> <code class="cpp color1 bold">char</code> <code class="cpp plain">*name);</code>
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setenv()是设置环境变量，如果成功则返回0，如果没有成功则返回非0</p>
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unsetenv()是删除一个环境变量</p>
<p>
下面提供一段程序大家可以自行的测试一下</p>
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<code class="cpp preprocessor">#include <stdio.h> </code>
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<code class="cpp preprocessor">#include <stdlib.h> </code>
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<code class="cpp preprocessor">#include <string.h> </code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">main(</code><code class="cpp keyword bold">void</code><code class="cpp plain">) </code>
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<code class="cpp plain">{ </code>
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<code class="cpp spaces">  </code><code class="cpp color1 bold">char</code><code class="cpp plain">* val; </code>
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<code class="cpp spaces">  </code><code class="cpp keyword bold">const</code> <code class="cpp color1 bold">char</code><code class="cpp plain">* name =</code><code class="cpp string">"ABC"</code><code class="cpp plain">; </code>
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<code class="cpp spaces">  </code><code class="cpp comments">//获取ABC环境变量的值 </code>
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<code class="cpp spaces">  </code><code class="cpp plain">val = </code><code class="cpp functions bold">getenv</code><code class="cpp plain">(name); </code>
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<code class="cpp spaces">  </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"No.1 %s=%s\n"</code><code class="cpp plain">, name, val); </code>
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<code class="cpp spaces">  </code><code class="cpp comments">//覆盖写入环境变量 </code>
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<code class="cpp spaces">  </code><code class="cpp plain">setenv(name, </code><code class="cpp string">"I amsure of that I will get it"</code><code class="cpp plain">, 1); </code>
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<code class="cpp spaces">  </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"No.2%s=%s\n"</code><code class="cpp plain">, name, val); </code>
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<code class="cpp spaces">  </code><code class="cpp plain">val = </code><code class="cpp functions bold">getenv</code><code class="cpp plain">(name); </code>
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<code class="cpp spaces">  </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"No.3%s=%s\n"</code><code class="cpp plain">, name, val); </code>
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<code class="cpp spaces">  </code><code class="cpp comments">//删除一个环境变量 </code>
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<code class="cpp spaces">  </code><code class="cpp color1 bold">int</code> <code class="cpp plain">ret =unsetenv(</code><code class="cpp string">"ABC"</code><code class="cpp plain">); </code>
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<code class="cpp spaces">  </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"ret =%d\n"</code><code class="cpp plain">,ret); </code>
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<code class="cpp spaces">  </code><code class="cpp plain">val = </code><code class="cpp functions bold">getenv</code><code class="cpp plain">(name); </code>
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<code class="cpp spaces">  </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"No.3 %s=%s\n"</code><code class="cpp plain">,name, val); </code>
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<code class="cpp spaces">  </code><code class="cpp keyword bold">return</code> <code class="cpp plain">0; </code>
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<code class="cpp plain">} </code>
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<p>
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。</p>
<p>
原文链接：http://blog.csdn.net/Neil4/article/details/72865497?utm_source=tuicool&utm_medium=referral</p>

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Linux下查看控制环境变量的方法