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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 行过滤器</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'writing-files';
}
if (e.key == "ArrowRight") {
window.location.href = 'file-paths';
}
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<body>
<div class="example" id="line-filters">
<h2><a href="./">Go by Example 中文版</a>: 行过滤器</h2>
<table>
<tr>
<td class="docs">
<p><em>行过滤器（line filter）</em> 是一种常见的程序类型，
它读取 stdin 上的输入，对其进行处理，然后将处理结果打印到 stdout。
<code>grep</code> 和 <code>sed</code> 就是常见的行过滤器。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
<p>这里是一个使用 Go 编写的行过滤器示例，它将所有的输入文字转化为大写的版本。
你可以使用这个模式来写一个你自己的 Go 行过滤器。</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/MNFcuZSD38b"><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">"bufio"</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>用带缓冲的 scanner 包装无缓冲的 <code>os.Stdin</code>，
这为我们提供了一种方便的 <code>Scan</code> 方法，
将 scanner 前进到下一个 <code>令牌</code>（默认为：下一行）。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">scanner</span> <span class="o">:=</span> <span class="nx">bufio</span><span class="p">.</span><span class="nf">NewScanner</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdin</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>Text</code> 返回当前的 token，这里指的是输入的下一行。</p>
</td>
<td class="code leading">
<pre class="chroma"> <span class="k">for</span> <span class="nx">scanner</span><span class="p">.</span><span class="nf">Scan</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">ucl</span> <span class="o">:=</span> <span class="nx">strings</span><span class="p">.</span><span class="nf">ToUpper</span><span class="p">(</span><span class="nx">scanner</span><span class="p">.</span><span class="nf">Text</span><span class="p">())</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>输出转换为大写后的行。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">ucl</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>检查 <code>Scan</code> 的错误。
文件结束符（EOF）是可以接受的，它不会被 <code>Scan</code> 当作一个错误。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="k">if</span> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">scanner</span><span class="p">.</span><span class="nf">Err</span><span class="p">();</span> <span class="nx">err</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Fprintln</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stderr</span><span class="p">,</span> <span class="s">"error:"</span><span class="p">,</span> <span class="nx">err</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">
<p>试一下我们的行过滤器，首先创建一个有小写行的文件。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> echo 'hello' > /tmp/lines
<span class="gp">$</span> echo 'filter' >> /tmp/lines</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>然后使用行过滤器来得到大写的行。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="gp">$</span> cat /tmp/lines | go run line-filters.go
<span class="go">HELLO
</span><span class="go">FILTER</span></pre>
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="file-paths.html">文件路径</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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