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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 命令行子命令</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'command-line-flags';
}
if (e.key == "ArrowRight") {
window.location.href = 'environment-variables';
}
}
</script>
<body>
<div class="example" id="command-line-subcommands">
<h2><a href="./">Go by Example 中文版</a>: 命令行子命令</h2>
<table>
<tr>
<td class="docs">
<p><code>go</code> 和 <code>git</code> 这种命令行工具，都有很多的 <em>子命令</em> 。
并且每个工具都有一套自己的 flag，比如：
<code>go build</code> 和 <code>go get</code> 是 <code>go</code> 里面的两个不同的子命令。
<code>flag</code> 包让我们可以轻松的为工具定义简单的子命令。</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/Eo69vIgCwLp"><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">"flag"</span>
<span class="s">"fmt"</span>
<span class="s">"os"</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>我们使用 <code>NewFlagSet</code> 函数声明一个子命令，
然后为这个子命令定义一个专用的 flag。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fooCmd</span> <span class="o">:=</span> <span class="nx">flag</span><span class="p">.</span><span class="nf">NewFlagSet</span><span class="p">(</span><span class="s">"foo"</span><span class="p">,</span> <span class="nx">flag</span><span class="p">.</span><span class="nx">ExitOnError</span><span class="p">)</span>
<span class="nx">fooEnable</span> <span class="o">:=</span> <span class="nx">fooCmd</span><span class="p">.</span><span class="nf">Bool</span><span class="p">(</span><span class="s">"enable"</span><span class="p">,</span> <span class="kc">false</span><span class="p">,</span> <span class="s">"enable"</span><span class="p">)</span>
<span class="nx">fooName</span> <span class="o">:=</span> <span class="nx">fooCmd</span><span class="p">.</span><span class="nf">String</span><span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">""</span><span class="p">,</span> <span class="s">"name"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>对于不同的子命令，我们可以定义不同的 flag。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">barCmd</span> <span class="o">:=</span> <span class="nx">flag</span><span class="p">.</span><span class="nf">NewFlagSet</span><span class="p">(</span><span class="s">"bar"</span><span class="p">,</span> <span class="nx">flag</span><span class="p">.</span><span class="nx">ExitOnError</span><span class="p">)</span>
<span class="nx">barLevel</span> <span class="o">:=</span> <span class="nx">barCmd</span><span class="p">.</span><span class="nf">Int</span><span class="p">(</span><span class="s">"level"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="s">"level"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>子命令应作为程序的第一个参数传入。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Args</span><span class="p">)</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="s">"expected 'foo' or 'bar' subcommands"</span><span class="p">)</span>
<span class="nx">os</span><span class="p">.</span><span class="nf">Exit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>检查哪一个子命令被调用了。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="k">switch</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Args</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>每个子命令，都会解析自己的 flag 并允许它访问后续的位置参数。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="k">case</span> <span class="s">"foo"</span><span class="p">:</span>
<span class="nx">fooCmd</span><span class="p">.</span><span class="nf">Parse</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Args</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="s">"subcommand '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">" enable:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">fooEnable</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">" name:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">fooName</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">" tail:"</span><span class="p">,</span> <span class="nx">fooCmd</span><span class="p">.</span><span class="nf">Args</span><span class="p">())</span>
<span class="k">case</span> <span class="s">"bar"</span><span class="p">:</span>
<span class="nx">barCmd</span><span class="p">.</span><span class="nf">Parse</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Args</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="s">"subcommand 'bar'"</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">" level:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">barLevel</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">" tail:"</span><span class="p">,</span> <span class="nx">barCmd</span><span class="p">.</span><span class="nf">Args</span><span class="p">())</span>
<span class="k">default</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">"expected 'foo' or 'bar' subcommands"</span><span class="p">)</span>
<span class="nx">os</span><span class="p">.</span><span class="nf">Exit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="gp">$</span> go build command-line-subcommands.go </pre>
</td>
</tr>
<tr>
<td class="docs">
<p>首先调用 foo 子命令。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> ./command-line-subcommands foo -enable -name=joe a1 a2
<span class="go">subcommand 'foo'
</span><span class="go"> enable: true
</span><span class="go"> name: joe
</span><span class="go"> tail: [a1 a2]</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>然后试一下 bar 子命令。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> ./command-line-subcommands bar -level 8 a1
<span class="go">subcommand 'bar'
</span><span class="go"> level: 8
</span><span class="go"> tail: [a1]</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>但是 bar 不接受 foo 的 flag（enable）。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> ./command-line-subcommands bar -enable a1
<span class="go">flag provided but not defined: -enable
</span><span class="go">Usage of bar:
</span><span class="go"> -level int
</span><span class="go"> level</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>接下来我们会学习程序获取参数的另一种常见方式——环境变量。</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="environment-variables">环境变量</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>
<script>
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