How to send input to a program through stdin in Rust

Question

I am attempting to write a shell in Rust. One of the functions of a shell is being able to redirect input to a file, redirect a file to input, and pipe output of a program into

Answer 1

This program demonstrates how you can launch external programs and stream their stdout -> stdin together:

use std::io::{BufRead, BufReader, BufWriter, Write};
use std::process::{Command, Stdio};

fn main() {
    // Create some argument vectors for lanuching external programs
    let a = vec!["view", "-h", "file.bam"];
    let outsam = vec!["view", "-bh", "-o", "rust.bam", "-"];

    let mut child = Command::new("samtools")
        .args(&a)
        .stdout(Stdio::piped())
        .spawn()
        .unwrap();
    let outchild = Command::new("samtools")
        .args(&outsam)
        .stdin(Stdio::piped())
        .spawn()
        .unwrap();

    // Create a handle and writer for the stdin of the second process
    let mut outstdin = outchild.stdin.unwrap();
    let mut writer = BufWriter::new(&mut outstdin);

    // Loop over the output from the first process
    if let Some(ref mut stdout) = child.stdout {
        for line in BufReader::new(stdout).lines() {

            let mut l: String = line.unwrap();
            // Need to add an end of line character back to the string
            let eol: &str = "\n";
            l = l + eol;

            // Print some select lines from the first child to stdin of second
            if (l.chars().skip(0).next().unwrap()) == '@' {
                // convert the string into bytes and write to second process
                let bytestring = l.as_bytes();
                writer.write_all(bytestring).unwrap();
            }
        }
    }
}