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<title>处理环境变量 - Rust 程序设计语言 简体中文版</title>
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<ul class="chapter"><li><a href="ch01-00-introduction.html"><strong>1.</strong> 介绍</a></li><li><ul class="section"><li><a href="ch01-01-installation.html"><strong>1.1.</strong> 安装</a></li><li><a href="ch01-02-hello-world.html"><strong>1.2.</strong> Hello, World!</a></li></ul></li><li><a href="ch02-00-guessing-game-tutorial.html"><strong>2.</strong> 猜猜看教程</a></li><li><a href="ch03-00-common-programming-concepts.html"><strong>3.</strong> 通用编程概念</a></li><li><ul class="section"><li><a href="ch03-01-variables-and-mutability.html"><strong>3.1.</strong> 变量和可变性</a></li><li><a href="ch03-02-data-types.html"><strong>3.2.</strong> 数据类型</a></li><li><a href="ch03-03-how-functions-work.html"><strong>3.3.</strong> 函数如何工作</a></li><li><a href="ch03-04-comments.html"><strong>3.4.</strong> 注释</a></li><li><a href="ch03-05-control-flow.html"><strong>3.5.</strong> 控制流</a></li></ul></li><li><a href="ch04-00-understanding-ownership.html"><strong>4.</strong> 认识所有权</a></li><li><ul class="section"><li><a href="ch04-01-what-is-ownership.html"><strong>4.1.</strong> 什么是所有权</a></li><li><a href="ch04-02-references-and-borrowing.html"><strong>4.2.</strong> 引用 & 借用</a></li><li><a href="ch04-03-slices.html"><strong>4.3.</strong> Slices</a></li></ul></li><li><a href="ch05-00-structs.html"><strong>5.</strong> 结构体</a></li><li><ul class="section"><li><a href="ch05-01-method-syntax.html"><strong>5.1.</strong> 方法语法</a></li></ul></li><li><a href="ch06-00-enums.html"><strong>6.</strong> 枚举和模式匹配</a></li><li><ul class="section"><li><a href="ch06-01-defining-an-enum.html"><strong>6.1.</strong> 定义枚举</a></li><li><a href="ch06-02-match.html"><strong>6.2.</strong> <code>match</code>控制流运算符</a></li><li><a href="ch06-03-if-let.html"><strong>6.3.</strong> <code>if let</code>简单控制流</a></li></ul></li><li><a href="ch07-00-modules.html"><strong>7.</strong> 模块</a></li><li><ul class="section"><li><a href="ch07-01-mod-and-the-filesystem.html"><strong>7.1.</strong> <code>mod</code>和文件系统</a></li><li><a href="ch07-02-controlling-visibility-with-pub.html"><strong>7.2.</strong> 使用<code>pub</code>控制可见性</a></li><li><a href="ch07-03-importing-names-with-use.html"><strong>7.3.</strong> 使用<code>use</code>导入命名</a></li></ul></li><li><a href="ch08-00-common-collections.html"><strong>8.</strong> 通用集合类型</a></li><li><ul class="section"><li><a href="ch08-01-vectors.html"><strong>8.1.</strong> vector</a></li><li><a href="ch08-02-strings.html"><strong>8.2.</strong> 字符串</a></li><li><a href="ch08-03-hash-maps.html"><strong>8.3.</strong> 哈希 map</a></li></ul></li><li><a href="ch09-00-error-handling.html"><strong>9.</strong> 错误处理</a></li><li><ul class="section"><li><a href="ch09-01-unrecoverable-errors-with-panic.html"><strong>9.1.</strong> <code>panic!</code>与不可恢复的错误</a></li><li><a href="ch09-02-recoverable-errors-with-result.html"><strong>9.2.</strong> <code>Result</code>与可恢复的错误</a></li><li><a href="ch09-03-to-panic-or-not-to-panic.html"><strong>9.3.</strong> <code>panic!</code>还是不<code>panic!</code></a></li></ul></li><li><a href="ch10-00-generics.html"><strong>10.</strong> 泛型、trait 和生命周期</a></li><li><ul class="section"><li><a href="ch10-01-syntax.html"><strong>10.1.</strong> 泛型数据类型</a></li><li><a href="ch10-02-traits.html"><strong>10.2.</strong> trait：定义共享的行为</a></li><li><a href="ch10-03-lifetime-syntax.html"><strong>10.3.</strong> 生命周期与引用有效性</a></li></ul></li><li><a href="ch11-00-testing.html"><strong>11.</strong> 测试</a></li><li><ul class="section"><li><a href="ch11-01-writing-tests.html"><strong>11.1.</strong> 编写测试</a></li><li><a href="ch11-02-running-tests.html"><strong>11.2.</strong> 运行测试</a></li><li><a href="ch11-03-test-organization.html"><strong>11.3.</strong> 测试的组织结构</a></li></ul></li><li><a href="ch12-00-an-io-project.html"><strong>12.</strong> 一个 I/O 项目</a></li><li><ul class="section"><li><a href="ch12-01-accepting-command-line-arguments.html"><strong>12.1.</strong> 接受命令行参数</a></li><li><a href="ch12-02-reading-a-file.html"><strong>12.2.</strong> 读取文件</a></li><li><a href="ch12-03-improving-error-handling-and-modularity.html"><strong>12.3.</strong> 增强错误处理和模块化</a></li><li><a href="ch12-04-testing-the-librarys-functionality.html"><strong>12.4.</strong> 测试库的功能</a></li><li><a href="ch12-05-working-with-environment-variables.html" class="active"><strong>12.5.</strong> 处理环境变量</a></li><li><a href="ch12-06-writing-to-stderr-instead-of-stdout.html"><strong>12.6.</strong> 输出到<code>stderr</code>而不是<code>stdout</code></a></li></ul></li></ul>
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<h1 class="menu-title">Rust 程序设计语言 简体中文版</h1>
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<a class="header" href="#处理环境变量" name="处理环境变量"><h2>处理环境变量</h2></a>
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<blockquote>
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<p><a href="https://github.com/rust-lang/book/blob/master/second-edition/src/ch12-05-working-with-environment-variables.md">ch12-05-working-with-environment-variables.md</a>
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<br>
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commit 4f2dc564851dc04b271a2260c834643dfd86c724</p>
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</blockquote>
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<p>让我们再增加一个功能：大小写不敏感搜索。另外，这个设定将不是一个命令行参数：相反它将是一个环境变量。当然可以选择创建一个大小写不敏感的命令行参数，不过用户要求提供一个环境变量这样设置一次之后在整个终端会话中所有的搜索都将是大小写不敏感的了。</p>
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<a class="header" href="#实现并测试一个大小写不敏感grep函数" name="实现并测试一个大小写不敏感grep函数"><h3>实现并测试一个大小写不敏感<code>grep</code>函数</h3></a>
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<p>首先，让我们增加一个新函数，当设置了环境变量时会调用它。增加一个新测试并重命名已经存在的那个：</p>
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<pre><code class="language-rust,ignore">#[cfg(test)]
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mod test {
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use {grep, grep_case_insensitive};
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#[test]
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fn case_sensitive() {
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let search = "duct";
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let contents = "\
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Rust:
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safe, fast, productive.
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Pick three.
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Duct tape.";
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assert_eq!(
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vec!["safe, fast, productive."],
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grep(search, contents)
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);
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}
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#[test]
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fn case_insensitive() {
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let search = "rust";
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let contents = "\
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Rust:
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safe, fast, productive.
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Pick three.
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Trust me.";
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assert_eq!(
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vec!["Rust:", "Trust me."],
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grep_case_insensitive(search, contents)
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);
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}
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}
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</code></pre>
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<!-- Will add ghosting and wingdings in libreoffice /Carol -->
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<p>我们将定义一个叫做<code>grep_case_insensitive</code>的新函数。它的实现与<code>grep</code>函数大体上相似，不过列表 12-16 展示了一些小的区别：</p>
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<figure>
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<span class="filename">Filename: src/lib.rs</span>
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<pre><code class="language-rust">fn grep_case_insensitive<'a>(search: &str, contents: &'a str) -> Vec<&'a str> {
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let search = search.to_lowercase();
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let mut results = Vec::new();
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for line in contents.lines() {
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if line.to_lowercase().contains(&search) {
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results.push(line);
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}
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}
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results
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}
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</code></pre>
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<figcaption>
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<p>Listing 12-16: Implementing a <code>grep_case_insensitive</code> function by changing the
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search string and the lines of the contents to lowercase before comparing them</p>
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</figcaption>
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</figure>
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<!-- Will add ghosting and wingdings in libreoffice /Carol -->
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<p>首先，将<code>search</code>字符串转换为小写，并存放于一个同名的覆盖变量中。注意现在<code>search</code>是一个<code>String</code>而不是字符串 slice，所以在将<code>search</code>传递给<code>contains</code>时需要加上 &，因为<code>contains</code>获取一个字符串 slice。</p>
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