cat

Cargo.toml

[package]
name = "cat"
version = "0.1.0"
authors = ["hrysd"]

[dependencies]
getopts = "0.2"

main.rs

extern crate getopts;

use getopts::Options;

use std::env;
use std::io;
use std::io::prelude::*;
use std::fs::File;

fn read_file(filename: String) -> Result<String, io::Error> {
    let mut file = try!(File::open(filename));
    let mut content = String::new();

    try!(file.read_to_string(&mut content));

    Ok(content)
}

fn print_line_with_numbers(filename: String) {
    let body = match read_file(filename) {
        Ok(content) => content,
        Err(reason) => panic!("{}", reason)
    };

    let splitted = body.split("\n");

    //println!("{:?}", splitted.count());

    let mut formatted: Vec<String> = Vec::new();

    for (index, line) in splitted.enumerate() {
        formatted.push(format!("{}: {}", index , line));
    }

    println!("{}", formatted.join("\n"))
}

fn main() {
    let args: Vec<String> = env::args().collect();

    let mut opts = Options::new();
    opts.optflag("n", "", "Number the output lines, starting at 1.");

    let matches = match opts.parse(&args[1..]) {
        Ok(m) => m,
        Err(f) => panic!(f.to_string())
    };

    if matches.opt_present("n") {
        print_line_with_numbers(args[1].clone())
    } else {
        println!("{}", read_file(args[1].clone()).unwrap())
    }
}