Rust 入门（四）：实战项目 - 构建命令行工具

Rust 入门系列（第 4 篇，共 5 篇） 前置阅读：第 3 篇 - 所有权、借用与生命周期 阅读时间：20 分钟

引言

前三篇学习了 Rust 的基础知识，这一篇我们来做一个实战项目：构建一个命令行文件搜索工具。

这个项目会用到：

✅ Clap：解析命令行参数
✅ 文件 I/O：读取文件内容
✅ 错误处理：Result 和 ? 操作符
✅ 迭代器和闭包

一、项目介绍

1.1 功能需求

构建一个类似 grep 的工具 minigrep：

bash

cargo run -- query filename.txt

功能：

在文件中搜索指定字符串
显示包含该字符串的所有行
支持大小写不敏感搜索

1.2 创建项目

bash

cargo new minigrep
cd minigrep

二、基础版本

2.1 读取命令行参数

rust

// src/main.rs
use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();
    println!("{:?}", args);
}

运行：

bash

$ cargo run -- query filename.txt
["target/debug/minigrep", "query", "filename.txt"]

2.2 提取参数

rust

fn main() {
    let args: Vec<String> = env::args().collect();

    let query = &args[1];
    let file_path = &args[2];

    println!("搜索: {}", query);
    println!("文件: {}", file_path);
}

2.3 读取文件

rust

use std::env;
use std::fs;

fn main() {
    let args: Vec<String> = env::args().collect();

    let query = &args[1];
    let file_path = &args[2];

    println!("搜索: {}", query);

    let contents = fs::read_to_string(file_path)
        .expect("无法读取文件");

    println!("文件内容:\n{}", contents);
}

测试：创建 poem.txt：

plaintext

I'm nobody! Who are you?
Are you nobody, too?
Then there's a pair of us - don't tell!
They'd banish us, you know.

运行：

bash

$ cargo run -- nobody poem.txt

三、重构：提高可维护性

3.1 提取配置

rust

struct Config {
    query: String,
    file_path: String,
}

impl Config {
    fn new(args: &[String]) -> Config {
        let query = args[1].clone();
        let file_path = args[2].clone();

        Config { query, file_path }
    }
}

fn main() {
    let args: Vec<String> = env::args().collect();
    let config = Config::new(&args);

    println!("搜索: {}", config.query);

    let contents = fs::read_to_string(config.file_path)
        .expect("无法读取文件");

    println!("文件内容:\n{}", contents);
}

3.2 错误处理

rust

impl Config {
    fn new(args: &[String]) -> Result<Config, &'static str> {
        if args.len() < 3 {
            return Err("参数不足");
        }

        let query = args[1].clone();
        let file_path = args[2].clone();

        Ok(Config { query, file_path })
    }
}

fn main() {
    let args: Vec<String> = env::args().collect();

    let config = Config::new(&args).unwrap_or_else(|err| {
        println!("参数解析错误: {}", err);
        std::process::exit(1);
    });

    // ...
}

3.3 提取核心逻辑

rust

fn main() {
    let args: Vec<String> = env::args().collect();

    let config = Config::new(&args).unwrap_or_else(|err| {
        println!("参数解析错误: {}", err);
        std::process::exit(1);
    });

    if let Err(e) = run(config) {
        println!("应用错误: {}", e);
        std::process::exit(1);
    }
}

fn run(config: Config) -> Result<(), Box<dyn std::error::Error>> {
    let contents = fs::read_to_string(config.file_path)?;

    for line in search(&config.query, &contents) {
        println!("{}", line);
    }

    Ok(())
}

fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
    let mut results = Vec::new();

    for line in contents.lines() {
        if line.contains(query) {
            results.push(line);
        }
    }

    results
}

运行：

bash

$ cargo run -- nobody poem.txt
I'm nobody! Who are you?
Are you nobody, too?

四、使用 Clap 改进

4.1 添加依赖

Clap 官方教程：

toml

# Cargo.toml
[dependencies]
clap = { version = "4.4", features = ["derive"] }

4.2 使用 Clap

rust

use clap::Parser;
use std::fs;

#[derive(Parser, Debug)]
#[command(name = "minigrep")]
#[command(about = "A simple grep clone in Rust", long_about = None)]
struct Args {
    /// 搜索的字符串
    query: String,

    /// 文件路径
    file_path: String,

    /// 大小写不敏感搜索
    #[arg(short, long)]
    ignore_case: bool,
}

fn main() {
    let args = Args::parse();

    if let Err(e) = run(args) {
        eprintln!("错误: {}", e);
        std::process::exit(1);
    }
}

fn run(args: Args) -> Result<(), Box<dyn std::error::Error>> {
    let contents = fs::read_to_string(&args.file_path)?;

    let results = if args.ignore_case {
        search_case_insensitive(&args.query, &contents)
    } else {
        search(&args.query, &contents)
    };

    for line in results {
        println!("{}", line);
    }

    Ok(())
}

fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
    contents
        .lines()
        .filter(|line| line.contains(query))
        .collect()
}

fn search_case_insensitive<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
    let query = query.to_lowercase();
    contents
        .lines()
        .filter(|line| line.to_lowercase().contains(&query))
        .collect()
}

使用示例：

bash

# 普通搜索
$ cargo run -- nobody poem.txt

# 大小写不敏感
$ cargo run -- NOBODY poem.txt -i

# 查看帮助
$ cargo run -- --help

五、测试

5.1 添加测试

rust

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn case_sensitive() {
        let query = "duct";
        let contents = "\
Rust:
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)
        );
    }
}

运行测试：

bash

cargo test

六、完整代码

6.1 main.rs

rust

use clap::Parser;
use std::fs;
use std::process;

#[derive(Parser, Debug)]
#[command(name = "minigrep")]
#[command(about = "A simple grep clone in Rust")]
struct Args {
    /// 搜索的字符串
    query: String,

    /// 文件路径
    file_path: String,

    /// 大小写不敏感搜索
    #[arg(short, long)]
    ignore_case: bool,
}

fn main() {
    let args = Args::parse();

    if let Err(e) = run(args) {
        eprintln!("应用错误: {}", e);
        process::exit(1);
    }
}

fn run(args: Args) -> Result<(), Box<dyn std::error::Error>> {
    let contents = fs::read_to_string(&args.file_path)?;

    let results = if args.ignore_case {
        search_case_insensitive(&args.query, &contents)
    } else {
        search(&args.query, &contents)
    };

    for line in results {
        println!("{}", line);
    }

    Ok(())
}

fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
    contents
        .lines()
        .filter(|line| line.contains(query))
        .collect()
}

fn search_case_insensitive<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
    let query = query.to_lowercase();
    contents
        .lines()
        .filter(|line| line.to_lowercase().contains(&query))
        .collect()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn case_sensitive() {
        let query = "duct";
        let contents = "Rust:\nsafe, fast, productive.\nPick three.\nDuct tape.";
        assert_eq!(vec!["safe, fast, productive."], search(query, contents));
    }

    #[test]
    fn case_insensitive() {
        let query = "rUsT";
        let contents = "Rust:\nsafe, fast, productive.\nPick three.\nTrust me.";
        assert_eq!(
            vec!["Rust:", "Trust me."],
            search_case_insensitive(query, contents)
        );
    }
}

七、扩展功能

7.1 添加行号

rust

fn search_with_line_numbers<'a>(query: &str, contents: &'a str) -> Vec<(usize, &'a str)> {
    contents
        .lines()
        .enumerate()
        .filter(|(_, line)| line.contains(query))
        .map(|(i, line)| (i + 1, line))
        .collect()
}

7.2 正则表达式支持

toml

[dependencies]
clap = { version = "4.4", features = ["derive"] }
regex = "1.10"

rust

use regex::Regex;

fn search_regex<'a>(pattern: &str, contents: &'a str) -> Vec<&'a str> {
    let re = Regex::new(pattern).expect("无效的正则表达式");
    contents
        .lines()
        .filter(|line| re.is_match(line))
        .collect()
}

7.3 多文件搜索

rust

use std::fs;
use std::path::PathBuf;

#[derive(Parser)]
struct Args {
    query: String,

    /// 文件路径（可以多个）
    #[arg(required = true)]
    files: Vec<PathBuf>,
}

fn main() {
    let args = Args::parse();

    for file_path in &args.files {
        println!("\n文件: {:?}", file_path);
        let contents = fs::read_to_string(file_path).expect("读取失败");
        let results = search(&args.query, &contents);
        for line in results {
            println!("{}", line);
        }
    }
}

八、学到了什么？

8.1 核心技能

命令行参数解析：使用 Clap
文件 I/O：fs::read_to_string
错误处理：Result 和 ? 操作符
迭代器：lines(), filter(), collect()
生命周期：函数返回引用
测试：单元测试

8.2 Rust 最佳实践

✅ 早期失败：参数错误立即退出
✅ 错误传播：使用 ? 简化代码
✅ 迭代器优先：避免手动循环
✅ 测试覆盖：核心逻辑都有测试

九、下一步

9.1 练习建议

添加更多选项（上下文行数、高亮显示等）
支持递归目录搜索
添加性能基准测试

9.2 推荐资源

系列总结

已完成：

Rust 是什么？能做什么？
基础语法与核心概念
所有权、借用与生命周期
实战项目 - CLI 工具

下一篇（最后一篇）：《Rust 入门（五）：Rust + WebAssembly》

参考资料

系列导航

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