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Mini Grep CLI

Updated
17 Sept 2026
5 min read
0 sections
Page 6 of 18
Rust
rust
use std::env;
use std::fs;

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

    let query = &args[1];
    let filename = &args[2];

    println!("Searching for {:?}", query);
    println!("In file {}", filename);

    let contents = fs::read_to_string(filename).expect("Something went wrong reading the file");

    println!("\n With text: \n\n{}", contents);
}
  • env::args{:rust} returns an iterator of the command-line arguments that were given to the program
  • this code is not safe, it will panic if the user does not provide enough arguments

Using Functions

  • parse_config(){:rust} function returns a tuple of string slices, which are references to the arguments
rust
use std::env;
use std::fs;

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

    let (query, filename) = parse_config(&args);

    println!("Searching for {:?}", query);
    println!("In file {}", filename);

    let contents = fs::read_to_string(filename).expect("Something went wrong reading the file");

    println!("\n With text: \n\n{}", contents);
}

fn parse_config(args: &[String]) -> (&str, &str) {
    let query = &args[1];
    let filename = &args[2];

    (query, filename)
}

Using Structs

  • Config{:rust} struct is created to hold the query and filename
rust
use std::env;
use std::fs;

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

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

    let config: Config = parse_config(&args);

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

    let contents =
        fs::read_to_string(config.filename).expect("Something went wrong reading the file");

    println!("\n With text: \n\n{}", contents);

}

fn parse_config(args: &[String]) -> Config {
    let query = args[1].clone();
    let filename = args[2].clone();

    Config { query, filename }
}

Using Methods

  • new(){:rust} method is created to initialize the Config struct
rust
use std::env;
use std::fs;

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

impl Config {
    fn new(args: &[String]) -> Config {
        let query = args[1].clone();
        let filename = args[2].clone();

        Config { query, filename }
    }
}

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

    let config: Config = Config::new(&args);

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

    let contents =
        fs::read_to_string(config.filename).expect("Something went wrong reading the file");

    println!("\n With text: \n\n{}", contents);
}

Error Handling

  • running the program without enough arguments will panic
Out · error
$ cargo run

thread 'main' panicked at src/main.rs:11:21:
index out of bounds: the len is 1 but the index is 1
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
error: process didn't exit successfully: `targetdebugminigrep.exe` (exit code: 101)
  • handling the error by returning a Result from the new(){:rust} method
rust
use std::env;
use std::fs;

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

impl Config {
    fn new(args: &[String]) -> Config {
        if args.len() < 3 {
            panic!("Not enough arguments")
        }

        let query = args[1].clone();
        let filename = args[2].clone();

        Config { query, filename }
    }
}

fn main() {

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

    let config: Config = Config::new(&args);

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

    let contents =
        fs::read_to_string(config.filename).expect("Something went wrong reading the file");

    println!("\n With text: \n\n{}", contents);

}
Out · error
$ cargo run

thread 'main' panicked at src/main.rs:12:13:
not enough arguments
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
error: process didn't exit successfully: `targetdebugminigrep.exe` (exit code: 101)
  • method returns Result<Config, &str>{:rust} instead of Config{:rust}
  • returning an Err variant if there are not enough arguments
  • wrapping return type with Ok{:rust} variant
rust
use std::env;
use std::fs;
use std::process;

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

impl Config {
    fn new(args: &[String]) -> Result<Config, &str> {
        if args.len() < 3 {
            return Err("Not enough arguments");
        }

        let query = args[1].clone();
        let filename = args[2].clone();

        Ok(Config { query, filename })
    }
}

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

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

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

    let contents =
        fs::read_to_string(config.filename).expect("Something went wrong reading the file");

    println!("\n With text: \n\n{}", contents);

}
Out · error
$ cargo run

Problem parsing arguments: Not enough arguments
error: process didn't exit successfully: `targetdebugminigrep.exe` (exit code: 1)

Implementing main logic outside main()

  • run(){:rust} function is created to handle the main logic
rust
struct Config {
    // --snip--
}

impl Config {
    // --snip--
}

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

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

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

    run(config);

}

fn run(config: Config) {
    let contents =
        fs::read_to_string(config.filename).expect("Something went wrong reading the file");

    println!("\n With text: \n\n{}", contents);
}

Graseful Handling Errors

  • unused Result that must be used
  • this Result may be an Err variant, which should be handled
rust
struct Config {
    // --snip--
}

impl Config {
    // --snip--
}

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

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

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

    println!("\n With text: \n\n{}", contents);

    Ok(())
}
  • Result<(), Box<dyn Error>>{:rust} is returned from the run(){:rust} function, which is a generic type that can hold any type of error
  • process::exit(1){:rust}
Out · error
$ cargo run test text.txt

Searching for "test"
In file text.txt
Application Error: The system cannot find the file specified. (os error 2)
error: process didn't exit successfully: `targetdebugminigrep.exe test text.txt` (exit code: 1)

Segetating code

rust
use std::env;
use std::process;

use minigrep::run;
use minigrep::Config;


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

    let config: Config = Config::new(&args).unwrap_or_else(|err| {
        println!("Problem parsing arguments: {}", 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);
    }
}
rust
use std::error::Error;
use std::fs;

pub struct Config {
    pub query: String,
    pub filename: String,
}

impl Config {
    pub fn new(args: &[String]) -> Result<Config, &str> {
        if args.len() < 3 {
            return Err("Not enough arguments");
        }

        let query = args[1].clone();
        let filename = args[2].clone();

        Ok(Config { query, filename })
    }
}


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

    println!("\n With text: \n\n{}", contents);

    Ok(())
}
rust
use std::error::Error;
use std::fs;

pub struct Config {
    pub query: String,
    pub filename: String,
}

impl Config {
    pub fn new(args: &[String]) -> Result<Config, &str> {
        if args.len() < 3 {
            return Err("Not enough arguments");
        }

        let query = args[1].clone();
        let filename = args[2].clone();

        Ok(Config { query, filename })
    }
}


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

    for line in search(&config.query, &contents) {
        println!("{}", line);
    }

    Ok(())
}

pub 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
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn one_rusult() {
        let query = "duct"; 
        let contents = "\
Rust:
safe, fast, productive.
Pick three.";

        assert_eq!(vec!["safe, fast, productive."], search(query, contents))
    } 
}
rust
use std::error::Error;
use std::fs;
use std::env;

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

impl Config {
    pub fn new(args: &[String]) -> Result<Config, &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 })
    }
}


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

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

    for line in search(&config.query, &contents) {
        println!("{}", line)
    }

    Ok(())
}

pub 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
}

pub 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.contains(&query) {
            results.push(line);
        }
    }

    results
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn case_sensitive() {
        let query = "duct"; 
        let contents = "\
Rust:
safe, fast, productive.
Pick three.
Duct tape.";

        assert_eq!(vec!["safe, fast, productive."], search(query, contents))
    } 

    #[test]
    fn case_insensitive() {
        let query = "rUsT";

        let contents = "\
        Rust:
        safe, fast, productive.
        Pick three.";

        assert_eq!(vec!["Rust:", "Trust me."], search_case_insensitive(query, contents))
    }
}