Rust by Example

The command line arguments can be accessed using std::env::args, which returns an iterator that yields a String for each argument:

use std::env;

fn main() {

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

// The first argument is the path that was used to call the program.

println!("My path is {}.", args[0]);

// The rest of the arguments are the passed command line parameters.

// Call the program like this:

// $ ./args arg1 arg2

println!("I got {:?} arguments: {:?}.", args.len() - 1, &args[1..]);

}

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$ ./args 1 2 3

My path is ./args.

I got 3 arguments: ["1", "2", "3"].

Crates

Alternatively, there are numerous crates that can provide extra functionality when creating command-line applications. The Rust Cookbook exhibits best practices on how to use one of the more popular command line argument crates, clap.

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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