Rust by Example

Argument parsing

Matching can be used to parse simple arguments:

use std::env;

fn increase(number: i32) {

println!("{}", number + 1);

}

fn decrease(number: i32) {

println!("{}", number - 1);

}

fn help() {

println!("usage:

match_args 

Check whether given string is the answer.

match_args {{increase|decrease}} 

Increase or decrease given integer by one.");

}

fn main() {

let args: Vec = env::args().collect();

match args.len() {

// no arguments passed

1 => {

println!("My name is 'match_args'. Try passing some arguments!");

},

// one argument passed

2 => {

match args[1].parse() {

Ok(42) => println!("This is the answer!"),

_ => println!("This is not the answer."),

}

},

// one command and one argument passed

3 => {

let cmd = &args[1];

let num = &args[2];

// parse the number

let number: i32 = match num.parse() {

Ok(n) => {

n

},

Err(_) => {

eprintln!("error: second argument not an integer");

help();

return;

},

};

// parse the command

match &cmd[..] {

"increase" => increase(number),

"decrease" => decrease(number),

_ => {

eprintln!("error: invalid command");

help();

},

}

},

// all the other cases

_ => {

// show a help message

help();

}

}

}

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$ ./match_args Rust

This is not the answer.

$ ./match_args 42

This is the answer!

$ ./match_args do something

error: second argument not an integer

usage:

match_args 

Check whether given string is the answer.

match_args {increase|decrease} 

Increase or decrease given integer by one.

$ ./match_args do 42

error: invalid command

usage:

match_args 

Check whether given string is the answer.

match_args {increase|decrease} 

Increase or decrease given integer by one.

$ ./match_args increase 42

43