Need Help Gathering Output and Status Code of a Program That Generates Large Amounts of Output

In my Rust application, I need to run an executable program, wait for it to terminate, and gather its output and status code. I'm currently using Command::spawn and wait_with_output to achieve this, which works well for small programs. However, when I run a program that generates a large amount of output, my Rust program hangs (at wait_with_output), and the child process becomes a zombie (<defunct>).

    let mut command_cmd = Command::new(executable);

    // spawn the exec
    let mut child_proc = match command_cmd.spawn() {
        Ok(output) => output,
        Err(e) => {

    let output = match child_proc.wait_with_output() {
        Ok(output) => output,
        Err(e) => {

    let stdout = String::from_utf8(output.stdout).unwrap();
    let status = output.status;

If I do child_proc.wait() without waiting for the output, the child finishes and returns a status code.

After researching online, I suspect that the large amount of output is causing the issue, but I'm not sure how to proceed. I need to collect the program's output and exit code for further processing.

Can anyone provide guidance on how to handle large amounts of program output while still gathering the exit code in Rust? Any help or advice would be greatly appreciated!

Interesting. You say wait_with_output vs. wait makes a difference, yet all that wait_with_output does beyond wait is to read from the spawned process’s pipe (in this case stdout).

Here’s the implementation, quite straightforward.

To make this question more easy to answer, it would probably useful if you could

  • confirm that a minimal change (e.g. just changing the name of the function being called) between using .wait_with_output and ignoring the result vs. using .wait and ignoring the result is really what makes the difference, and
  • give an estimation of what kind of size you are talking about when saying “a large amount of output”
1 Like

Ignoring result from .wait_with_output gave no change, same.

Number of chars of output - around 3000

If you just want to execute the command, wait for it to return and get its output why can't you use the output method of Command ? That will give the status code and every output of your command.

FYI: I would consider 3000 chars to be very small.


.output does same as .wait_with_output

It maybe because of the child app, but it seems okay what I can observe.
from cli and via .wait it works

Can you show your actual code? Code we can compile.

that's the actual code, I just remove error messages

By actual code I mean code we can compile and run such as this (or this using output directly. (the large comment is just to make the output larger than 3000 chars)

This runs without any issues.

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