Rust: Start process. Keep StdOut and StdErr in the original order. Display output real time character by character. Capture output on exit.

process_example.rs

// Add to your Cargo.toml:
// [dependencies]
// utf8-chars = "1.0.0"
// subprocess = { version = "0.2.10", git = "https://github.com/SCP002/rust-subprocess.git" }

use std::io;
use std::io::BufReader;
use std::io::Write;
use subprocess::Exec;
use subprocess::ExitStatus;
use subprocess::Redirection;
use utf8_chars::BufReadCharsExt;

fn main() {
    let mut proc = Exec::cmd("my-executable-name")
        .arg("arg1")
        .stdout(Redirection::Pipe)
        .stderr(Redirection::Merge)
        .popen()
        .unwrap();

    let mut out = String::new();

    BufReader::new(proc.stdout.as_ref().unwrap())
        .chars()
        .filter_map(|c| c.ok())
        .for_each(|c| {
            print!("{}", c);
            io::stdout().flush().unwrap();
            out.push(c);
        });

    let exit_status = proc.wait().unwrap();

    println!("{}", "-".repeat(30));
    println!("{}", out);
    let exit_code = match exit_status {
        ExitStatus::Exited(c) => c as i32,
        _ => -1,
    };
    println!("Exit code: {:?}", exit_code);
}