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<main>
<h1 id="调用系统命令"><a class="header" href="#调用系统命令">调用系统命令</a></h1>
<h3 id="调用一个外部命令并处理输出内容"><a class="header" href="#调用一个外部命令并处理输出内容">调用一个外部命令并处理输出内容</a></h3>
<p>下面的代码将调用操作系统中的 <code>git log --oneline</code> 命令，然后使用 <a href="https://docs.rs/regex/*/regex/struct.Regex.html">regex</a> 对它输出到 <code>stdout</code> 上的调用结果进行解析，以获取哈希值和最后 5 条提交信息( commit )。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021"><span class="boring">use error_chain::error_chain;
</span>
use std::process::Command;
use regex::Regex;
<span class="boring">error_chain!{
</span><span class="boring"> foreign_links {
</span><span class="boring"> Io(std::io::Error);
</span><span class="boring"> Regex(regex::Error);
</span><span class="boring"> Utf8(std::string::FromUtf8Error);
</span><span class="boring"> }
</span><span class="boring">}
</span>
#[derive(PartialEq, Default, Clone, Debug)]
struct Commit {
hash: String,
message: String,
}
fn main() -&gt; Result&lt;()&gt; {
let output = Command::new(&quot;git&quot;).arg(&quot;log&quot;).arg(&quot;--oneline&quot;).output()?;
if !output.status.success() {
error_chain::bail!(&quot;Command executed with failing error code&quot;);
}
let pattern = Regex::new(r&quot;(?x)
([0-9a-fA-F]+) # commit hash
(.*) # The commit message&quot;)?;
String::from_utf8(output.stdout)?
.lines()
.filter_map(|line| pattern.captures(line))
.map(|cap| {
Commit {
hash: cap[1].to_string(),
message: cap[2].trim().to_string(),
}
})
.take(5)
.for_each(|x| println!(&quot;{:?}&quot;, x));
Ok(())
}</code></pre></pre>
<h3 id="调用-python-解释器运行代码并检查返回的错误码"><a class="header" href="#调用-python-解释器运行代码并检查返回的错误码">调用 python 解释器运行代码并检查返回的错误码</a></h3>
<pre><pre class="playground"><code class="language-rust editable edition2021"><span class="boring">use error_chain::error_chain;
</span>
use std::collections::HashSet;
use std::io::Write;
use std::process::{Command, Stdio};
<span class="boring">error_chain!{
</span><span class="boring"> errors { CmdError }
</span><span class="boring"> foreign_links {
</span><span class="boring"> Io(std::io::Error);
</span><span class="boring"> Utf8(std::string::FromUtf8Error);
</span><span class="boring"> }
</span><span class="boring">}
</span>
fn main() -&gt; Result&lt;()&gt; {
let mut child = Command::new(&quot;python&quot;).stdin(Stdio::piped())
.stderr(Stdio::piped())
.stdout(Stdio::piped())
.spawn()?;
child.stdin
.as_mut()
.ok_or(&quot;Child process stdin has not been captured!&quot;)?
.write_all(b&quot;import this; copyright(); credits(); exit()&quot;)?;
let output = child.wait_with_output()?;
if output.status.success() {
let raw_output = String::from_utf8(output.stdout)?;
let words = raw_output.split_whitespace()
.map(|s| s.to_lowercase())
.collect::&lt;HashSet&lt;_&gt;&gt;();
println!(&quot;Found {} unique words:&quot;, words.len());
println!(&quot;{:#?}&quot;, words);
Ok(())
} else {
let err = String::from_utf8(output.stderr)?;
error_chain::bail!(&quot;External command failed:\n {}&quot;, err)
}
}</code></pre></pre>
<h3 id="通过管道来运行外部命令"><a class="header" href="#通过管道来运行外部命令">通过管道来运行外部命令</a></h3>
<p>下面的例子将显示当前目录中大小排名前十的文件和子目录，效果等效于命令 <code>du -ah . | sort -hr | head -n 10</code>。</p>
<p><a href="https://doc.rust-lang.org/std/process/struct.Command.html"><code>Command</code></a> 命令代表一个进程，其中父进程通过 <a href="https://doc.rust-lang.org/std/process/struct.Stdio.html">Stdio::piped</a> 来捕获子进程的输出。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021"><span class="boring">use error_chain::error_chain;
</span>
use std::process::{Command, Stdio};
<span class="boring">error_chain! {
</span><span class="boring"> foreign_links {
</span><span class="boring"> Io(std::io::Error);
</span><span class="boring"> Utf8(std::string::FromUtf8Error);
</span><span class="boring"> }
</span><span class="boring">}
</span>
fn main() -&gt; Result&lt;()&gt; {
let directory = std::env::current_dir()?;
let mut du_output_child = Command::new(&quot;du&quot;)
.arg(&quot;-ah&quot;)
.arg(&amp;directory)
.stdout(Stdio::piped())
.spawn()?;
if let Some(du_output) = du_output_child.stdout.take() {
let mut sort_output_child = Command::new(&quot;sort&quot;)
.arg(&quot;-hr&quot;)
.stdin(du_output)
.stdout(Stdio::piped())
.spawn()?;
du_output_child.wait()?;
if let Some(sort_output) = sort_output_child.stdout.take() {
let head_output_child = Command::new(&quot;head&quot;)
.args(&amp;[&quot;-n&quot;, &quot;10&quot;])
.stdin(sort_output)
.stdout(Stdio::piped())
.spawn()?;
let head_stdout = head_output_child.wait_with_output()?;
sort_output_child.wait()?;
println!(
&quot;Top 10 biggest files and directories in '{}':\n{}&quot;,
directory.display(),
String::from_utf8(head_stdout.stdout).unwrap()
);
}
}
Ok(())
}</code></pre></pre>
<h3 id="将子进程的-stdout-和-stderr-重定向到同一个文件"><a class="header" href="#将子进程的-stdout-和-stderr-重定向到同一个文件">将子进程的 stdout 和 stderr 重定向到同一个文件</a></h3>
<p>下面的例子将生成一个子进程，然后将它的标准输出和标准错误输出都输出到同一个文件中。最终的效果跟 Unix 命令 <code>ls . oops &gt;out.txt 2&gt;&amp;1</code> 相同。</p>
<p><a href="https://doc.rust-lang.org/std/fs/struct.File.html#method.try_clone">File::try_clone</a> 会克隆一份文件句柄的引用，然后保证这两个句柄在写的时候会使用相同的游标位置。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use std::fs::File;
use std::io::Error;
use std::process::{Command, Stdio};
fn main() -&gt; Result&lt;(), Error&gt; {
let outputs = File::create(&quot;out.txt&quot;)?;
let errors = outputs.try_clone()?;
Command::new(&quot;ls&quot;)
.args(&amp;[&quot;.&quot;, &quot;oops&quot;])
.stdout(Stdio::from(outputs))
.stderr(Stdio::from(errors))
.spawn()?
.wait_with_output()?;
Ok(())
}</code></pre></pre>
<h3 id="持续处理子进程的输出"><a class="header" href="#持续处理子进程的输出">持续处理子进程的输出</a></h3>
<p>下面的代码会创建一个管道，然后当 <code>BufReader</code> 更新时，就持续从 <code>stdout</code> 中读取数据。最终效果等同于 Unix 命令 <code>journalctl | grep usb</code>。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use std::process::{Command, Stdio};
use std::io::{BufRead, BufReader, Error, ErrorKind};
fn main() -&gt; Result&lt;(), Error&gt; {
let stdout = Command::new(&quot;journalctl&quot;)
.stdout(Stdio::piped())
.spawn()?
.stdout
.ok_or_else(|| Error::new(ErrorKind::Other,&quot;Could not capture standard output.&quot;))?;
let reader = BufReader::new(stdout);
reader
.lines()
.filter_map(|line| line.ok())
.filter(|line| line.find(&quot;usb&quot;).is_some())
.for_each(|line| println!(&quot;{}&quot;, line));
Ok(())
}</code></pre></pre>
<h3 id="读取环境变量"><a class="header" href="#读取环境变量">读取环境变量</a></h3>
<p>使用 <a href="https://doc.rust-lang.org/std/env/fn.var.html">std::env::var</a> 可以读取系统中的环境变量。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use std::env;
use std::fs;
use std::io::Error;
fn main() -&gt; Result&lt;(), Error&gt; {
// 读取环境变量 `CONFIG` 的值并写入到 `config_path` 中。
// 若 `CONFIG` 环境变量没有设置，则使用一个默认的值 &quot;/etc/myapp/config&quot;
let config_path = env::var(&quot;CONFIG&quot;)
.unwrap_or(&quot;/etc/myapp/config&quot;.to_string());
let config: String = fs::read_to_string(config_path)?;
println!(&quot;Config: {}&quot;, config);
Ok(())
}</code></pre></pre>
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