Reading and Writing Files

We need some way to actually get data from the filesystem so we can process it, and write it back when we’re done
我们需要某种方法从文件系统中实际获取数据，以便处理它，并在完成后将其写回来

rust">use std::fs;

std::fs::read_to_string returns a Result<String, std::io::Error>.
If the function succeeds, it produces a String. If it fails, it produces a std::io::Error, the standard library’s type for representing I/O problems.
std::fs::read_to_string返回Result<String, std::io::Error>。
如果函数成功，它将生成一个String。如果失败，它会产生std::io::Error，这是表示I/O问题的标准库类型。

rust">fn main() {let args = parse_args();let data = match fs::read_to_string(&args.filename) { Ok(v) => v,Err(e) => {eprintln!("{} failed to read from file '{}': {:?}","Error:".red().bold(), args.filename, e);std::process::exit(1);} };match fs::write(&args.output, &data) { Ok(_) => {},Err(e) => {eprintln!("{} failed to write to file '{}': {:?}","Error:".red().bold(), args.filename, e);std::process::exit(1);} };
}

Find and Replace

The final touch for this program is to implement its actual functionality: finding and replacing. For this, we’ll use the regex crate, which compiles and executes regular expressions. It provides a struct called Regex, which represents a compiled regular expression. Regex has a method replace_all, which does exactly what it says: it searches a string for all matches of the regular expression and replaces each one with a given replacement string. We can pull this logic out into a function:

这个程序的最后一步是实现它的实际功能:查找和替换。为此，我们将使用regex crate，它编译并执行正则表达式。它提供了一个名为Regex的结构体，它表示编译后的正则表达式。Regex有一个方法replace_all，它所做的正是它所说的:它在字符串中搜索正则表达式的所有匹配项，并用给定的替换字符串替换每个匹配项。我们可以把这个逻辑放到一个函数中:

rust">use regex::Regex;
fn replace(target: &str, replacement: &str, text: &str)-> Result<String, regex::Error>{let regex = Regex::new(target)?;Ok(regex.replace_all(text, replacement).to_string())}

rust">fn main() {let args = parse_args();let data = match fs::read_to_string(&args.filename) { Ok(v) => v,Err(e) => {eprintln!("{} failed to read from file '{}': {:?}","Error:".red().bold(), args.filename, e);std::process::exit(1);} };let replaced_data = match replace(&args.target, &args.replacement, &data) {Ok(v) => v,Err(e) => {eprintln!("{} failed to replace text: {:?}","Error:".red().bold(), e);std::process::exit(1);}};match fs::write(&args.output, &replaced_data) { Ok(v) => v,Err(e) => {eprintln!("{} failed to write to file '{}': {:?}","Error:".red().bold(), args.filename, e);std::process::exit(1);} };
}

rust">$ echo "Hello, world" > test.txt
$ cargo run "world" "Rust" test.txt test-modified.txt
$ cat test-modified.txt 
Hello, Rust