minigrep demo from rust book.

minigrep.rs

use std::env;
use std::process;
use std::fs;
use std::error::Error;

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

    let config = Config::new(&args).unwrap_or_else(|err|{
        println!("Problem parsing arguements: {}", err);
        process::exit(1);
    });

    println!("Searching for {}", config.query);
    println!("in file {}", config.filename);

    if let Err(e) = run(config) {
        println!("Application error: {}", e);
        process::exit(1);
    }
}

struct Config {
    query: String,
    filename: String,
    case_sensitive: bool,
}

impl Config {
    fn new(args: &[String]) -> Result<Config, &'static str> {
        if args.len() < 3 {
            return Err("not enough arguments");
        }
        let query = args[1].clone();
        let filename = args[2].clone();

        let case_sensitive = env::var("CASE_INSENSITIVE").is_err();

        Ok(Config { query, filename, case_sensitive })
    }
}

fn run(config: Config) -> Result<(), Box<dyn Error>> {
    let content = fs::read_to_string(config.filename)?;

    let results = if config.case_sensitive {
        search(&config.query, &content)
    } else {
        search_case_insensitive(&config.query, &content)
    };

    for line in results {
        println!("{}", line);
    }

    Ok(())
}

fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
    let mut results = Vec::new();

    for line in contents.lines() {
        if line.contains(&query) {
            results.push(line);
        }
    }

    results
}

fn search_case_insensitive<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
    let query = query.to_lowercase();
    let mut results = Vec::new();

    for line in contents.lines() {
        if line.to_lowercase().contains(&query) {
            results.push(line);
        }
    }

    results
}