A simple secure password generator

main.rs

extern crate rand;
extern crate docopt;
extern crate rustc_serialize;

use rand::{OsRng, Rng};
use docopt::Docopt;

static USAGE: &'static str = "
Usage: rpgen [options]
       rpgen --help

Options:
    -h, --help             Shows this message.
    -l, --length <chars>   Generates a password with this many chars [default: 10].
    -a, --amount <amount>  Generates this many passwords [default: 1].
";

#[derive(RustcDecodable, Debug)]
struct Args {
   flag_length: usize,
   flag_amount: usize
}

fn main() {
    let args: Args = Docopt::new(USAGE)
                           .and_then(|d| d.decode())
                           .unwrap_or_else(|e| e.exit());


    let choices:Vec<char> = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890+*~#!§$%&/()=?[]{}'-_.,;:<>|\\\"".chars().collect();
    let length = args.flag_length;
    let mut amount = args.flag_amount;

    while amount > 0 {
        println!("{}", gen_pw(&choices, length));
        amount -= 1;
    }
}

fn gen_pw(choices: &Vec<char>, length: usize) -> String {
    let mut rng = OsRng::new().unwrap();
    let mut new_password = String::new();
    while new_password.len() < length {
        let new_char = rng.choose(&choices).unwrap().to_string();
        new_password = new_password + &new_char;
    }

    return new_password;
}