My very best and first Rust program. This was written for 0.8.

cat.rs

extern mod extra;

use extra::getopts;
use extra::fileinput;
use std::os;
use std::io;

fn main() {
  let args = os::args();
  let program = args[0].clone();

  let opts = ~[
      getopts::groups::optflag("h", "help", "Kind help text"),
      getopts::groups::optflag("s", "squeeze", "TODO: haha - Squeeze multiple adjacent empty lines, causing the output to be single spaced"),
      getopts::groups::optflag("b", "line-numbers", "Number the non-blank output lines, starting at 1")
      
  ];
  let matches = match getopts::groups::getopts(args.tail(), opts) {
    Ok(m) => { m }
    Err(f) => { fail!(f.to_err_msg()) }
  };
  if matches.opt_present("help") {
     print_usage(program, opts);
     return;
  }
  let filename: &str = if !matches.free.is_empty() {
    matches.free[0].clone()
  } else {
    print_usage(program, opts);
    return;
  };
  do_work(filename, matches);
}

fn print_usage(program: &str, opts: &[getopts::groups::OptGroup]) {
    println(getopts::groups::usage(program, opts));
}

fn do_work(filename: &str, matches: getopts::Matches) {
  let mut i = 0;
  fileinput::FileInput::from_vec(fileinput::make_path_option_vec(&[filename.into_owned()], true)).each_line( |line| {
      if !line.is_empty() {
        i += 1;
        if matches.opt_present("line-numbers") {
          io::print(fmt!("\t%d\t", i));
        }
      }

      io::println(line);
      true
  });
}