Rust でテキストファイルの読み込み

// --------------------------------------------------------------------
/*
    text_read.rs

                        Jul/09/2020
*/
// --------------------------------------------------------------------
use std::env;
use std::error;
use std::fs::File;
use std::io::{BufRead, BufReader};

fn main() -> Result<(), Box<dyn error::Error>> {

eprintln!("*** 開始 ***");

let args: Vec<_> = env::args().collect();

let ref fname_in = args[1];

for result in BufReader::new(File::open(fname_in)?).lines() {
    let ll = result?;
    println!("{}", ll);
    }

eprintln!("*** 終了 ***");
Ok(())

}
// ---------------------------------------------------------------------

text_read: text_read.rs
    rustc text_read.rs
clean:
    rm -f text_read

$ make
rustc text_read.rs

$ ./text_read cities.txt 
*** 開始 ***
t2381   名古屋   71842   2005-9-12
t2382   豊橋  14278   2005-3-15
t2383   岡崎  65291   1950-10-2
t2384   一宮  31864   1950-6-22
t2385   蒲郡  49158   1950-8-14
*** 終了 ***