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<main>
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<h1 id="使用环境变量来增强程序"><a class="header" href="#使用环境变量来增强程序">使用环境变量来增强程序</a></h1>
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<p>在上一章节中，留下了一个悬念，该如何实现用户控制的大小写敏感，其实答案很简单，你在其它程序中肯定也遇到过不少，例如如何控制 <code>panic</code> 后的栈展开？ Rust 提供的解决方案是通过命令行参数来控制:</p>
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<pre><code class="language-shell">RUST_BACKTRACE=1 cargo run
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</code></pre>
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<p>与之类似，我们也可以使用环境变量来控制大小写敏感，例如:</p>
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<pre><code class="language-shell">IGNORE_CASE=1 cargo run -- to poem.txt
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</code></pre>
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<p>既然有了目标，那么一起来看看该如何实现吧。</p>
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<h2 id="编写大小写不敏感的测试用例"><a class="header" href="#编写大小写不敏感的测试用例">编写大小写不敏感的测试用例</a></h2>
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<p>还是遵循之前的规则：测试驱动，这次是对一个新的大小写不敏感函数进行测试 <code>search_case_insensitive</code>。</p>
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<p>还记得 TDD 的测试步骤嘛？首先编写一个注定失败的用例:</p>
|
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<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
|
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</span>// in src/lib.rs
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn case_sensitive() {
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let query = "duct";
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let contents = "\
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Rust:
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|
|
safe, fast, productive.
|
|
|
Pick three.
|
|
|
Duct tape.";
|
|
|
|
|
|
assert_eq!(vec!["safe, fast, productive."], search(query, contents));
|
|
|
}
|
|
|
|
|
|
#[test]
|
|
|
fn case_insensitive() {
|
|
|
let query = "rUsT";
|
|
|
let contents = "\
|
|
|
Rust:
|
|
|
safe, fast, productive.
|
|
|
Pick three.
|
|
|
Trust me.";
|
|
|
|
|
|
assert_eq!(
|
|
|
vec!["Rust:", "Trust me."],
|
|
|
search_case_insensitive(query, contents)
|
|
|
);
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p>可以看到，这里新增了一个 <code>case_insensitive</code> 测试用例，并对 <code>search_case_insensitive</code> 进行了测试，结果显而易见，函数都没有实现，自然会失败。</p>
|
|
|
<p>接着来实现这个大小写不敏感的搜索函数:</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>pub fn search_case_insensitive<'a>(
|
|
|
query: &str,
|
|
|
contents: &'a str,
|
|
|
) -> Vec<&'a str> {
|
|
|
let query = query.to_lowercase();
|
|
|
let mut results = Vec::new();
|
|
|
|
|
|
for line in contents.lines() {
|
|
|
if line.to_lowercase().contains(&query) {
|
|
|
results.push(line);
|
|
|
}
|
|
|
}
|
|
|
|
|
|
results
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p>跟之前一样，但是引入了一个新的方法 <code>to_lowercase</code>，它会将 <code>line</code> 转换成全小写的字符串，类似的方法在其它语言中也差不多，就不再赘述。</p>
|
|
|
<p>还要注意的是 <code>query</code> 现在是 <code>String</code> 类型，而不是之前的 <code>&str</code>，因为 <code>to_lowercase</code> 返回的是 <code>String</code>。</p>
|
|
|
<p>修改后，再来跑一次测试，看能否通过。</p>
|
|
|
<pre><code class="language-shell">$ cargo test
|
|
|
Compiling minigrep v0.1.0 (file:///projects/minigrep)
|
|
|
Finished test [unoptimized + debuginfo] target(s) in 1.33s
|
|
|
Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
|
|
|
|
|
|
running 2 tests
|
|
|
test tests::case_insensitive ... ok
|
|
|
test tests::case_sensitive ... ok
|
|
|
|
|
|
test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
|
|
|
|
|
|
Running unittests src/main.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
|
|
|
|
|
|
running 0 tests
|
|
|
|
|
|
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
|
|
|
|
|
|
Doc-tests minigrep
|
|
|
|
|
|
running 0 tests
|
|
|
|
|
|
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
|
|
|
</code></pre>
|
|
|
<p>Ok，TDD的第二步也完成了，测试通过，接下来就是最后一步，在 <code>run</code> 中调用新的搜索函数。但是在此之前，要新增一个配置项，用于控制是否开启大小写敏感。</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>// in lib.rs
|
|
|
pub struct Config {
|
|
|
pub query: String,
|
|
|
pub file_path: String,
|
|
|
pub ignore_case: bool,
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p>接下来就是检查该字段，来判断是否启动大小写敏感：</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>pub fn run(config: Config) -> Result<(), Box<dyn Error>> {
|
|
|
let contents = fs::read_to_string(config.file_path)?;
|
|
|
|
|
|
let results = if config.ignore_case {
|
|
|
search_case_insensitive(&config.query, &contents)
|
|
|
} else {
|
|
|
search(&config.query, &contents)
|
|
|
};
|
|
|
|
|
|
for line in results {
|
|
|
println!("{line}");
|
|
|
}
|
|
|
|
|
|
Ok(())
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p>现在的问题来了，该如何控制这个配置项呢。这个就要借助于章节开头提到的环境变量，好在 Rust 的 <code>env</code> 包提供了相应的方法。</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>use std::env;
|
|
|
// --snip--
|
|
|
|
|
|
impl Config {
|
|
|
pub fn build(args: &[String]) -> Result<Config, &'static str> {
|
|
|
if args.len() < 3 {
|
|
|
return Err("not enough arguments");
|
|
|
}
|
|
|
|
|
|
let query = args[1].clone();
|
|
|
let file_path = args[2].clone();
|
|
|
|
|
|
let ignore_case = env::var("IGNORE_CASE").is_ok();
|
|
|
|
|
|
Ok(Config {
|
|
|
query,
|
|
|
file_path,
|
|
|
ignore_case,
|
|
|
})
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p><code>env::var</code> 没啥好说的，倒是 <code>is_ok</code> 值得说道下。该方法是 <code>Result</code> 提供的，用于检查是否有值，有就返回 <code>true</code>，没有则返回 <code>false</code>，刚好完美符合我们的使用场景，因为我们并不关心 <code>Ok<T></code> 中具体的值。</p>
|
|
|
<p>运行下试试：</p>
|
|
|
<pre><code class="language-shell">$ cargo run -- to poem.txt
|
|
|
Compiling minigrep v0.1.0 (file:///projects/minigrep)
|
|
|
Finished dev [unoptimized + debuginfo] target(s) in 0.0s
|
|
|
Running `target/debug/minigrep to poem.txt`
|
|
|
Are you nobody, too?
|
|
|
How dreary to be somebody!
|
|
|
</code></pre>
|
|
|
<p>看起来没有问题，接下来测试下大小写不敏感:</p>
|
|
|
<pre><code class="language-shell">$ IGNORE_CASE=1 cargo run -- to poem.txt
|
|
|
</code></pre>
|
|
|
<pre><code class="language-shell">Are you nobody, too?
|
|
|
How dreary to be somebody!
|
|
|
To tell your name the livelong day
|
|
|
To an admiring bog!
|
|
|
</code></pre>
|
|
|
<p>大小写不敏感后，查询到的内容明显多了很多，也很符合我们的预期。</p>
|
|
|
<p>最后，给大家留一个小作业：同时使用命令行参数和环境变量的方式来控制大小写不敏感，其中环境变量的优先级更高，也就是两个都设置的情况下，优先使用环境变量的设置。</p>
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