how can I get stdin to exec cmd in golang

Question

I have this code

subProcess := exec.Cmd{
    Path: execAble,
    Args: []string{
        fmt.Sprintf(\"-config=%s\", *configPath),
        fmt.Sprintf(\"-serverT         


        

Answer 1

I made a simple program (for testing). It reads a number and writes the given number out.

package main

import (
    "fmt"
)

func main() {
    fmt.Println("Hello, What's your favorite number?")
    var i int
    fmt.Scanf("%d\n", &i)
    fmt.Println("Ah I like ", i, " too.")
}

And here is the modified code

package main

import (
    "fmt"
    "io"
    "os"
    "os/exec"
)

func main() {
    subProcess := exec.Command("go", "run", "./helper/main.go") //Just for testing, replace with your subProcess

    stdin, err := subProcess.StdinPipe()
    if err != nil {
        fmt.Println(err) //replace with logger, or anything you want
    }
    defer stdin.Close() // the doc says subProcess.Wait will close it, but I'm not sure, so I kept this line

    subProcess.Stdout = os.Stdout
    subProcess.Stderr = os.Stderr

    fmt.Println("START") //for debug
    if err = subProcess.Start(); err != nil { //Use start, not run
        fmt.Println("An error occured: ", err) //replace with logger, or anything you want
    }

    io.WriteString(stdin, "4\n")
    subProcess.Wait()
    fmt.Println("END") //for debug
}

You interested about these lines

stdin, err := subProcess.StdinPipe()
if err != nil {
    fmt.Println(err)
}
defer stdin.Close()
//...
io.WriteString(stdin, "4\n")
//...
subProcess.Wait()

Explanation of the above lines

1. We gain the subprocess' stdin, now we can write to it
2. We use our power and we write a number
3. We wait for our subprocess to complete

Output

START
Hello, What's your favorite number?
Ah I like 4 too.
END

For better understanding