I am trying to execute a command in a shell and get the return value as a string. The command I'm trying to execute is ps axww | grep mongod | grep -v grep

I've seen solutions over the internet, but they don't explain the code, so it is hard customising it to my needs.

example: how to do a sandwich pipe in rust? & Pipe between two child processes

can someone please provide a solution and go line by line explaining how it works in layman's terms.

Much apreciated :)

CodePudding user response：

What you need is the documentation, where they do explain everything line by line, with thorough examples. Adapted from it, here is your code

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

fn main() {
    let ps_child = Command::new("ps") // `ps` command...
        .arg("axww")                  // with argument `axww`...
        .stdout(Stdio::piped())       // of which we will pipe the output.
        .spawn()                      // Once configured, we actually spawn the command...
        .unwrap();                    // and assert everything went right.
    let grep_child_one = Command::new("grep")
        .arg("mongod")
        .stdin(Stdio::from(ps_child.stdout.unwrap())) // Pipe through.
        .stdout(Stdio::piped())
        .spawn()
        .unwrap();
    let grep_child_two = Command::new("grep")
        .arg("-v")
        .arg("grep")
        .stdin(Stdio::from(grep_child_one.stdout.unwrap()))
        .stdout(Stdio::piped())
        .spawn()
        .unwrap();
    let output = grep_child_two.wait_with_output().unwrap();
    let result = str::from_utf8(&output.stdout).unwrap();
    println!("{}", result);
}

See the playground (which of course won't output anything since there is no process called mongod running...).