Combine files with cat

Question

I am trying to combine files with cat using Rust. Below is some example code that is erroring with the below error.

use std::process::Command as cmd;
cmd::new("/bin/cat")
    .arg("1.txt 2.txt > 3.txt")
    .spawn()
    .expect("Failure");

/bin/cat: '1.txt 2.txt > 3.txt': No such file or directory

I also tried adding it as multiple arguments with

cmd::new("/bin/cat")
    .args("1.txt 2.txt", ">", "3.txt")
    .spawn()
    .expect("Failure");

which errors out with

/bin/cat: '1.txt 2.txt': No such file or directory
/bin/cat: '>': No such file or directory
/bin/cat: 3.txt: No such file or directory

I've tried with cmd::new("/bin/sh") but that doesn't work either.

Answer 1

Here are two examples considering the suggestions in the comments.

fn main() {
    // redirect output from rust
    std::process::Command::new("/bin/cat")
        .args(["1.txt", "2.txt"])
        .stdout(std::fs::File::create("3.txt").unwrap())
        .spawn()
        .expect("spawn failure")
        .wait()
        .expect("wait failure");
    //
    // rely on the shell for redirection
    std::process::Command::new("/bin/sh")
        .args(["-c", "cat 1.txt 2.txt >3_bis.txt"])
        .spawn()
        .expect("spawn failure")
        .wait()
        .expect("wait failure");
}

Answer 2

A simpler and more robust solution is to use std::fs instead of cat:

use std::fs;

let file1 = fs::read_to_string("1.txt").expect("1.txt could not be opened");
let file2 = fs::read_to_string("2.txt").expect("2.txt could not be opened");

fs::write("3.txt", file1 + "\n" + &file2).expect("3.txt could not be written");

Note that this doesn't depend on cat, it works on every platform and operating system, and it allows handling each error properly.