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environment-variables.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 环境变量</title>
<link rel=stylesheet href="site.css">
</head>
<script>
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<body>
<div class="example" id="environment-variables">
<h2><a href="./">Go by Example 中文版</a>: 环境变量</h2>
<table>
<tr>
<td class="docs">
<p><a href="http://zh.wikipedia.org/wiki/%E7%8E%AF%E5%A2%83%E5%8F%98%E9%87%8F"><em>环境变量</em></a>
是一种<a href="http://www.12factor.net/config">向 Unix 程序传递配置信息</a>的常见方式。
让我们来看看如何设置、获取以及列出环境变量。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://play.studygolang.com/p/II_mSnaUZJo"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
<span class="s">"fmt"</span>
<span class="s">"os"</span>
<span class="s">"strings"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>使用 <code>os.Setenv</code> 来设置一个键值对。
使用 <code>os.Getenv</code>获取一个键对应的值。
如果键不存在，将会返回一个空字符串。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">os</span><span class="p">.</span><span class="nf">Setenv</span><span class="p">(</span><span class="s">"FOO"</span><span class="p">,</span> <span class="s">"1"</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"FOO:"</span><span class="p">,</span> <span class="nx">os</span><span class="p">.</span><span class="nf">Getenv</span><span class="p">(</span><span class="s">"FOO"</span><span class="p">))</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"BAR:"</span><span class="p">,</span> <span class="nx">os</span><span class="p">.</span><span class="nf">Getenv</span><span class="p">(</span><span class="s">"BAR"</span><span class="p">))</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>使用 <code>os.Environ</code> 来列出所有环境变量键值对。
这个函数会返回一个 <code>KEY=value</code> 形式的字符串切片。
你可以使用 <code>strings.SplitN</code> 来得到键和值。这里我们打印所有的键。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">()</span>
<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">os</span><span class="p">.</span><span class="nf">Environ</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">pair</span> <span class="o">:=</span> <span class="nx">strings</span><span class="p">.</span><span class="nf">SplitN</span><span class="p">(</span><span class="nx">e</span><span class="p">,</span> <span class="s">"="</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">pair</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>运行这个程序，显示我们在程序中设置的 <code>FOO</code> 的值，
然而没有设置的 <code>BAR</code> 是空的。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> go run environment-variables.go
<span class="go">FOO: 1
</span><span class="go">BAR: </span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>键的列表是由你的电脑情况而定的。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="go">TERM_PROGRAM
</span><span class="go">PATH
</span><span class="go">SHELL
</span><span class="go">...</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>如果我们在运行前设置了 <code>BAR</code> 的值，那么运行程序将会获取到这个值。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="gp">$</span> BAR=2 go run environment-variables.go
<span class="go">FOO: 1
</span><span class="go">BAR: 2
</span><span class="go">...</span></pre>
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="http-clients">HTTP 客户端</a>
</p>
<p class="footer">
<a href="https://twitter.com/mmcgrana">@mmcgrana</a> 和<a href="https://eli.thegreenplace.net">Eli Bendersky</a>编写 | <a href="https://github.com/gobyexample-cn">gobyexample-cn</a> 翻译 | <a href="https://github.com/gobyexample-cn/gobyexample/issues">反馈</a> | <a href="https://github.com/gobyexample-cn/gobyexample">源码</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> </p>
</p>
</div>
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