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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 命令行标志</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'command-line-arguments';
}
if (e.key == "ArrowRight") {
window.location.href = 'command-line-subcommands';
}
}
</script>
<body>
<div class="example" id="command-line-flags">
<h2><a href="./">Go by Example 中文版</a>: 命令行标志</h2>
<table>
<tr>
<td class="docs">
<p><a href="http://en.wikipedia.org/wiki/Command-line_interface#Command-line_option"><em>命令行标志</em></a>
是命令行程序指定选项的常用方式。例如，在 <code>wc -l</code> 中，
这个 <code>-l</code> 就是一个命令行标志。</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/IpbanTVOJ4d"><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">
<p>Go 提供了一个 <code>flag</code> 包，支持基本的命令行标志解析。
我们将用这个包来实现我们的命令行程序示例。</p>
</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="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>基本的标记声明仅支持字符串、整数和布尔值选项。
这里我们声明一个默认值为 <code>"foo"</code> 的字符串标志 <code>word</code> 并带有一个简短的描述。
这里的 <code>flag.String</code> 函数返回一个字符串指针（不是一个字符串值），
在下面我们会看到是如何使用这个指针的。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">wordPtr</span> <span class="o">:=</span> <span class="nx">flag</span><span class="p">.</span><span class="nf">String</span><span class="p">(</span><span class="s">"word"</span><span class="p">,</span> <span class="s">"foo"</span><span class="p">,</span> <span class="s">"a string"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>使用和声明 <code>word</code> 标志相同的方法来声明 <code>numb</code> 和 <code>fork</code> 标志。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">numbPtr</span> <span class="o">:=</span> <span class="nx">flag</span><span class="p">.</span><span class="nf">Int</span><span class="p">(</span><span class="s">"numb"</span><span class="p">,</span> <span class="mi">42</span><span class="p">,</span> <span class="s">"an int"</span><span class="p">)</span>
<span class="nx">forkPtr</span> <span class="o">:=</span> <span class="nx">flag</span><span class="p">.</span><span class="nf">Bool</span><span class="p">(</span><span class="s">"fork"</span><span class="p">,</span> <span class="kc">false</span><span class="p">,</span> <span class="s">"a bool"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>用程序中已有的参数来声明一个标志也是可以的。
注意在标志声明函数中需要使用该参数的指针。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">var</span> <span class="nx">svar</span> <span class="kt">string</span>
<span class="nx">flag</span><span class="p">.</span><span class="nf">StringVar</span><span class="p">(</span><span class="o">&</span><span class="nx">svar</span><span class="p">,</span> <span class="s">"svar"</span><span class="p">,</span> <span class="s">"bar"</span><span class="p">,</span> <span class="s">"a string var"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>所有标志都声明完成以后，调用 <code>flag.Parse()</code> 来执行命令行解析。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">flag</span><span class="p">.</span><span class="nf">Parse</span><span class="p">()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>这里我们将仅输出解析的选项以及后面的位置参数。
注意，我们需要使用类似 <code>*wordPtr</code> 这样的语法来对指针解引用，
从而得到选项真正的值。</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="s">"word:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">wordPtr</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">"numb:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">numbPtr</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">"fork:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">forkPtr</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">"svar:"</span><span class="p">,</span> <span class="nx">svar</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">flag</span><span class="p">.</span><span class="nf">Args</span><span class="p">())</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>测试这个程序前，最好将这个程序编译成二进制文件，然后再运行这个程序。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> go build command-line-flags.go</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>首先以给所有标志赋值的方式，尝试运行构建的程序。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> ./command-line-flags -word=opt -numb=7 -fork -svar=flag
<span class="go">word: opt
</span><span class="go">numb: 7
</span><span class="go">fork: true
</span><span class="go">svar: flag
</span><span class="go">tail: []</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>注意，如果你省略一个标志，那么这个标志的值自动的设定为他的默认值。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> ./command-line-flags -word=opt
<span class="go">word: opt
</span><span class="go">numb: 42
</span><span class="go">fork: false
</span><span class="go">svar: bar
</span><span class="go">tail: []</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>尾随的位置参数可以出现在任何标志后面。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> ./command-line-flags -word=opt a1 a2 a3
<span class="go">word: opt
</span><span class="go">...
</span><span class="go">tail: [a1 a2 a3]</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>注意，<code>flag</code> 包需要所有的标志出现位置参数之前（否则，这个标志将会被解析为位置参数）。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> ./command-line-flags -word=opt a1 a2 a3 -numb=7
<span class="go">word: opt
</span><span class="go">numb: 42
</span><span class="go">fork: false
</span><span class="go">svar: bar
</span><span class="go">tail: [a1 a2 a3 -numb=7]</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>使用 <code>-h</code> 或者 <code>--help</code> 标志来得到自动生成的这个命令行程序的帮助文本。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> ./command-line-flags -h
<span class="go">Usage of ./command-line-flags:
</span><span class="go"> -fork=false: a bool
</span><span class="go"> -numb=42: an int
</span><span class="go"> -svar="bar": a string var
</span><span class="go"> -word="foo": a string</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>如果你提供了一个没有使用 <code>flag</code> 包声明的标志，
程序会输出一个错误信息，并再次显示帮助文本。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="gp">$</span> ./command-line-flags -wat
<span class="go">flag provided but not defined: -wat
</span><span class="go">Usage of ./command-line-flags:
</span><span class="go">...</span></pre>
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="command-line-subcommands">命令行子命令</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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