Combine files with cat - rust

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.