从命令行读取参数

use std::env;

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

ai@aisty:/opt/wks/rust/rfil/rcmd/target/debug$ ./rcmd aa bb cc
["./rcmd", "aa", "bb", "cc"]

第一个参数是命令本身

The args Function and Invalid Unicode

Note that std::env::args will panic if any argument contains invalid Unicode. If your program needs to accept arguments containing invalid Unicode, use std::env::args_os instead. That function returns an iterator that produces OsString values instead of String values. We’ve chosen to use std::env::args here for simplicity, because OsString values differ per platform and are more complex to work with than String values.

索引为0的参数是命令本身，从索引为1的参数开始才是输入的参数

use std::env;

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

let query = &args\[1\];  
let filename = &args\[2\];

println!("Searching for {}", query);  
println!("In file {}", filename);  

}

ai@aisty:/opt/wks/rust/rfil/rcmd$ cargo run name /tmp/aa.txt
Finished dev [unoptimized + debuginfo] target(s) in 0.00s
Running `target/debug/rcmd name /tmp/aa.txt`
Searching for name
In file /tmp/aa.txt

读取指定的文件内容

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

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

let filename = &args\[1\];  
println!("In file {}", filename);

let contents = fs::read\_to\_string(filename)  
    .expect("Something went wrong reading the file");

println!("With text:\\n{}", contents);

}

ai@aisty:/opt/wks/rust/rfil/rcmd$ cargo run /tmp/aa.txt
Compiling rcmd v0.1.0 (/opt/wks/rust/rfil/rcmd)
Finished dev [unoptimized + debuginfo] target(s) in 0.21s
Running `target/debug/rcmd /tmp/aa.txt`
In file /tmp/aa.txt
With text:
aa

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

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

let (query, filename) = parse\_config(&args);

// --snip--

println!("Searching for {}", query);  
println!("In file {}", filename);

let contents = fs::read\_to\_string(filename)  
    .expect("Something went wrong reading the file");

println!("With text:\\n{}", contents);  

}

fn parse_config(args: &[String]) -> (&str, &str) {
let query = &args[1];
let filename = &args[2];

(query, filename)  

}

ai@aisty:/opt/wks/rust/rfil/rcmd$ cargo run aa /tmp/aa.log
Finished dev [unoptimized + debuginfo] target(s) in 0.00s
Running `target/debug/rcmd aa /tmp/aa.log`
Searching for aa
In file /tmp/aa.log
With text:
aa
bb

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

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

let config = parse\_config(&args);

println!("Searching for {}", config.query);  
println!("In file {}", config.filename);

let contents = fs::read\_to\_string(config.filename)  
    .expect("Something went wrong reading the file");

println!("With text:\\n{}", contents);  

}

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

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

Config { query, filename }  

}

clone性能不好，后面会介绍其他方式

There’s a tendency among many Rustaceans to avoid using clone to fix ownership problems because of its runtime cost.

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

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

let config = Config::new(&args);

println!("Searching for {}", config.query);  
println!("In file {}", config.filename);

let contents = fs::read\_to\_string(config.filename)  
    .expect("Something went wrong reading the file");

println!("With text:\\n{}", contents);

}

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

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

    Config { query, filename }  
}  

}

添加自定义错误

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

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

let config = Config::new(&args);

println!("Searching for {}", config.query);  
println!("In file {}", config.filename);

let contents = fs::read\_to\_string(config.filename)  
    .expect("Something went wrong reading the file");

println!("With text:\\n{}", contents);

}

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

impl Config {
fn new(args: &[String]) -> Config {
if args.len() < 3 {
panic!("not enough arguments");
}

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

    Config { query, filename }  
}  

}

Returning a Result from new Instead of Calling panic!