How can I run a binary file in my golang program and keep interacting with it by sending some input and waiting for the output?

Question

How can I run a binary file in my golang program and keep interacting with it by sending some input and waiting for the output? In what I did, I run it only once. And I want to keep this binary file running and interact with it, I don't want to run it multiple times.

package main

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

func main() {
    command := exec.Command("./program")
    var output bytes.Buffer
    command.Stdout = &output
    command.Run()
    result := output.String()
    IV := result[:4]
    cipher := result[5:]
    cipher = cipher[:len(cipher)-1]
    fmt.Printf("%v", result)
    fmt.Printf("%v", IV)
    fmt.Printf("%v", cipher)
}

Go aside, how do you currently interact with your program? Stdin / Stdout? Pipes? Sockets? — sberry
– sberry, Commented Feb 6, 2019 at 1:24
I don't know how this could work, that is what I'm trying to figure out. I wish someone could guide me in this. The binary that I'm trying to interact with receives an input and give and output and waits for another input. So what I want to do is interacting with it in that way. — Maha Alrasheed
– Maha Alrasheed, Commented Feb 6, 2019 at 1:36
It sounds like you are interacting with stdin and stdout then. Take a look here: stackoverflow.com/questions/36382880/… — sberry
– sberry, Commented Feb 6, 2019 at 1:40
I'm trying stdin, but I don't know how I can write to the binary not to my program. — Maha Alrasheed
– Maha Alrasheed, Commented Feb 6, 2019 at 1:43

Eli Bendersky · Accepted Answer · 2019-02-06 13:58:18Z

I believe the right way to accomplish this is using the StdinPipe and StdoutPipe methods of exec.Cmd.

See examples in https://golang.org/pkg/os/exec/#Cmd.StdinPipe, etc.

Here's an example that invokes the bc command (built-in calculator that takes calculations from stdin and emits results to stdout) and interacts with it a bit:

package main

import (
    "bufio"
    "fmt"
    "log"
    "os/exec"
)

func main() {
    cmd := exec.Command("bc", "-q")

    stdin, err := cmd.StdinPipe()
    if err != nil {
        log.Fatal(err)
    }

    stdout, err := cmd.StdoutPipe()
    if err != nil {
        log.Fatal(err)
    }

    if err := cmd.Start(); err != nil {
        log.Fatal(err)
    }

    stdin.Write([]byte("2 + 2\n"))

    r := bufio.NewReader(stdout)
    b, err := r.ReadBytes('\n')
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println("Read:", string(b))
}

In a real program you may want to run this thing in a goroutine so it doesn't block the rest of the application, happens in the background, etc.

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