How would you stream output from a Process?

Question

I believe I understand, in general, one way of doing this:

• Create a Command
• Use Stdio::piped() to create a new pair of outpu

Answer 1

I'll happily accept any example of spawning a long running process and streaming output to the console, by whatever means.

It sounds like you want Stdio::inherit:

use std::process::{Command, Stdio};

fn main() {
    let mut cmd =
        Command::new("cat")
        .args(&["/usr/share/dict/web2"])
        .stdout(Stdio::inherit())
        .stderr(Stdio::inherit())
        .spawn()
        .unwrap();

    // It's streaming here

    let status = cmd.wait();
    println!("Exited with status {:?}", status);
}

Answer 2

Although the accepted answer is correct, it doesn't cover the non-trivial case.

To stream output and handle it manually, use Stdio::piped() and manually handle the .stdout property on the child returned from calling spawn, like this:

use std::process::{Command, Stdio};
use std::path::Path;
use std::io::{BufReader, BufRead};

pub fn exec_stream<P: AsRef<Path>>(binary: P, args: Vec<&'static str>) {
    let mut cmd = Command::new(binary.as_ref())
        .args(&args)
        .stdout(Stdio::piped())
        .spawn()
        .unwrap();

    {
        let stdout = cmd.stdout.as_mut().unwrap();
        let stdout_reader = BufReader::new(stdout);
        let stdout_lines = stdout_reader.lines();

        for line in stdout_lines {
            println!("Read: {:?}", line);
        }
    }

    cmd.wait().unwrap();
}

#[test]
fn test_long_running_process() {
    exec_stream("findstr", vec!("/s", "sql", "C:\\tmp\\*"));
}

See also Merge child process stdout and stderr regarding catching the output from stderr and stdout simultaneously.