Understanding the utility
了解实用程序

Running the pwd command, we get an output like this
运行 pwd 命令，我们得到如下输出

# pwd
/root/

Here /root is the directory that we are currently in, in the Linux Shell
这里 /root 是我们当前所在的目录，在 Linux Shell 中

To recreate this, it’s really not difficult and we can recreate this without any trouble using the std::env::current_dir() function, Let’s create a library crate inside a new Rust project and a module to get started with this.
要重新创建它，实际上并不困难，我们可以使用 std::env::current_dir() 函数毫无困难地重新创建它，让我们在新的 Rust 项目中创建一个库箱和一个模块来开始使用它。

//lib.rs

pub mod dir_get {
  use std::env;
  use std::path::PathBuf;

  fn get_working_directory() -> std::io::Resullt<PathBuf> {
    env::current_dir()
  }
}

The get_working_directoryfunction runs the env::current_dir() function and returns a result enum with a PathBuf or an Err variant.
get_working_directory 函数运行 env::current_dir() 函数并返回带有 PathBuf 或 Err 变体的结果枚举。

We will do the error handing in the next part…
我们将在下一部分中进行错误处理......

According to the documentation of this ffunction we can see that there are two cases in which this function will return an error:
根据这个ffunction的文档我们可以看到这个函数有两种情况会返回错误：

• Current directory does not exist.
  当前目录不存在。
• There are insufficient permissions to access the current directory.
  没有足够的权限访问当前目录。

Check out the documentation here :
查看此处的文档：current_dir in std::env - Rust (rust-lang.org)

Now to create a function which prints the PathBuf while handling the errors :
现在创建一个在处理错误时打印 PathBuf 的函数：

//lib.rs

pub mod dir_get {
  use std::env;
  use std::path::PathBuf;

  fn get_working_directory() -> std::io::Resullt<PathBuf> {
    env::current_dir()
  }

  pub fn print_working_dir() {
    let result = get_working_directory();
    match result {
      Ok(path_buf) => println!("{}",path_buf.as_path().display()),
      Err(e) => eprintln!("Application Error: {}",e),
    };
  }
}

Now that’s all we’ll have to do with the library crate, let’s get to the main.rs file and call the print_working_dirfunction there and check if it works?
现在这就是我们对库箱要做的所有事情，让我们进入 main.rs 文件并调用其中的 print_working_dir 函数并检查它是否有效？

//main.rs
use pwd::dir_get; //use the name of your crate and module here

fn main(){
  dir_get::print_working_dir();
}

And it’s done, running the program with cargo run we get the following response
就完成了，使用 cargo run 运行程序，我们得到以下响应

# pwd #The GNU utility
/root/learning_rust/linux_tools/pwd
# cargo run #The utility that we just built
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/pwd`
/root/learning_rust/linux_tools/pwd

Conclusion 结论

Lib.rs :

pub mod dir_get: This declares a module named dir_get, which can be accessed from other modules.
pub mod dir_get ：这声明了一个名为 dir_get 的模块，可以从其他模块访问该模块。

• use std::env;: This imports the env module from the standard library, which provides functions for interacting with the environment variables of the current process.
  use std::env; ：从标准库导入 env 模块，该模块提供与当前进程的环境变量交互的函数。
• use std::path::PathBuf;: This imports the PathBuf struct from the std::path module, which represents an owned, mutable path.
  use std::path::PathBuf; ：这会从 std::path 模块导入 PathBuf 结构，该结构表示拥有的可变路径。

fn get_working_directory() -> std::io::Result<PathBuf>: This defines a function named get_working_directory that returns a result containing a PathBuf representing the current working directory, wrapped in std::io::Result.
fn get_working_directory() -> std::io::Result<PathBuf> ：这定义了一个名为 get_working_directory 的函数，该函数返回一个结果，其中包含表示当前工作目录的 PathBuf ，包装在 std::io::Result 中。

• env::current_dir(): This is a function from the env module that returns a Result<PathBuf, std::io::Error> representing the current working directory.
  env::current_dir() ：这是 env 模块中的一个函数，它返回表示当前工作目录的 Result<PathBuf, std::io::Error> 。

pub fn print_working_dir(): This defines a public function named print_working_dir, which takes no arguments.
pub fn print_working_dir() ：这定义了一个名为 print_working_dir 的公共函数，它不带任何参数。

• let result = get_working_directory();: This calls the get_working_directory function and stores the result in the result variable.
  let result = get_working_directory(); ：调用 get_working_directory 函数并将结果存储在 result 变量中。
• match result { ... }: This is a match expression that handles the result of calling get_working_directory(). It matches on the Ok variant, which contains the successfully obtained PathBuf, and the Err variant, which contains an error if the operation failed.
  match result { ... } ：这是一个 match 表达式，用于处理调用 get_working_directory() 的结果。它与 Ok 变体（包含成功获取的 PathBuf ）和 Err 变体（如果操作失败则包含错误）匹配。
• Ok(path_buf) => println!("{}", path_buf.as_path().display()),: If get_working_directory() succeeds, this branch is executed, printing the current working directory using path_buf.as_path().display().
  Ok(path_buf) => println!("{}", path_buf.as_path().display()), ：如果 get_working_directory() 成功，则执行此分支，并使用 path_buf.as_path().display() 打印当前工作目录。
• Err(e) => eprintln!("Application Error: {}", e),: If get_working_directory() fails, this branch is executed, printing an error message indicating that an application error occurred.
  Err(e) => eprintln!("Application Error: {}", e), ：如果 get_working_directory() 失败，则执行此分支，打印一条错误消息，指示发生应用程序错误。

Main.rs

• use pwd::dir_get;: This line imports the print_working_dir function from the dir_get module defined in the pwd crate. This allows us to use the function in the current scope.
  use pwd::dir_get; ：此行从 pwd 包中定义的 dir_get 模块导入 print_working_dir 函数。这允许我们在当前范围内使用该函数。
• fn main() { ... }: This defines the main function, which serves as the entry point of the program.
  fn main() { ... } ：定义主函数，作为程序的入口点。
• dir_get::print_working_dir();: This line calls the print_working_dir function from the dir_get module. It is prefixed with dir_get:: to specify that the function is being called from the dir_get module.
  dir_get::print_working_dir(); ：此行从 dir_get 模块调用 print_working_dir 函数。它以 dir_get:: 为前缀，以指定从 dir_get 模块调用该函数。
• The main function does not take any arguments.
  main 函数不接受任何参数。
• When executed, this program will print the current working directory to the standard output.
  执行时，该程序会将当前工作目录打印到标准输出。
• The print_working_dir function is defined in the dir_get module and is responsible for obtaining and printing the current working directory.
  print_working_dir 函数定义在 dir_get 模块中，负责获取并打印当前工作目录。