main.rs

extern crate regex;

use std::env;
use std::error;
use std::fs::File;
use std::io::{self, BufRead, Write};
use std::process;

use regex::bytes::Regex;

type Error = Box<error::Error + Send + Sync>;

fn main() {
    match run() {
        Ok(count) => println!("{}", count),
        Err(err) => {
            let _ = writeln!(&mut io::stderr(), "{}", err);
            process::exit(1);
        }
    }
}

fn run() -> Result<u64, Error> {
    let (fpath, query) = match (env::args_os().nth(1), env::args().nth(2)) {
        (None, _) => return Err(Error::from("missing file to search")),
        (_, None) => return Err(Error::from("missing search query")),
        (Some(fpath), Some(query)) => (fpath, query),
    };
    let query_re = Regex::new(&regex::quote(&query))?;
    let mut count = 0;
    let mut rdr = io::BufReader::new(File::open(fpath)?);
    let mut line = vec![];
    while rdr.read_until(b'\n', &mut line)? > 0 {
        if query_re.is_match(&line) {
            count += 1;
        }
        line.clear();
    }
    Ok(count)
}