Rust by Example

proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

";

use std::fs::File;

use std::io::prelude::*;

use std::path::Path;

fn main() {

let path = Path::new("lorem_ipsum.txt");

let display = path.display();

// Open a file in write-only mode, returns `io::Result`

let mut file = match File::create(&path) {

Err(why) => panic!("couldn't create {}: {}", display, why),

Ok(file) => file,

};

// Write the `LOREM_IPSUM` string to `file`, returns `io::Result<()>`

match file.write_all(LOREM_IPSUM.as_bytes()) {

Err(why) => panic!("couldn't write to {}: {}", display, why),

Ok(_) => println!("successfully wrote to {}", display),

}

}

Here's the expected successful output:

$ rustc create.rs && ./create

successfully wrote to lorem_ipsum.txt

$ cat lorem_ipsum.txt

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod

tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,

quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo

consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse

cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non

proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

(As in the previous example, you are encouraged to test this example under failure conditions.)

There is OpenOptions struct that can be used to configure how a file is opened.

read_lines

The method lines() returns an iterator over the lines of a file.

File::open expects a generic, AsRef. That's what read_lines() expects as input.

use std::fs::File;

use std::io::{self, BufRead};

use std::path::Path;

fn main() {

// File hosts must exist in current path before this produces output

if let Ok(lines) = read_lines("./hosts") {

// Consumes the iterator, returns an (Optional) String

for line in lines {

if let Ok(ip) = line {

println!("{}", ip);

}

}

}

}

// The output is wrapped in a Result to allow matching on errors

// Returns an Iterator to the Reader of the lines of the file.

fn read_lines

(filename: P) -> io::Result>>

where P: AsRef, {

let file = File::open(filename)?;

Ok(io::BufReader::new(file).lines())

}

Running this program simply prints the lines individually.

$ echo -e "127.0.0.1\n192.168.0.1\n" > hosts

$ rustc read_lines.rs && ./read_lines

127.0.0.1

192.168.0.1

This process is more efficient than creating a String in memory especially working with larger files.

Child processes

The process::Output struct represents the output of a finished child process, and the process::Command struct is a process builder.

use std::process::Command;

fn main() {

let output = Command::new("rustc")

.arg("--version")

.output().unwrap_or_else(|e| {

panic!("failed to execute process: {}", e)

});

if output.status.success() {

let s = String::from_utf8_lossy(&output.stdout);

print!("rustc succeeded and stdout was:\n{}", s);

} else {