4.2 rust 命令行参数

 从命令行读取参数

use std::env;

fn main() {
    let args: Vec<String> = 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<String> = 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<String> = 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:
{}", 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<String> = 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:
{}", 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<String> = 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:
{}", 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<String> = 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:
{}", 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<String> = 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:
{}", 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!