一旦在golang中准备好从stdout管道读取

Question

I'm facing with a weird golang issue. The following code will clarify:

package main

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

var (
    pw io.WriteCloser
    pr io.ReadCloser
)

func main() {
    term := exec.Command("/bin/sh")

    // Get stdin writer pipe
    pw, _ = term.StdinPipe()
    pr, _ = term.StdoutPipe()

    term.Start()

    run("cd ~")
    pwd := run("pwd");

    // Do something with pwd output
    ...

    term.Wait()
}

func run(c string) string {
    io.WriteString(pw, fmt.Sprintln(c))

    buf := make([]byte, 32 * 1024)
    pr.Read(buf)
    return string(buf)
}

I'd like to run some commands in a shell env and read their output. There's no problem on write/run command but it seems that there're some limitations while reading:

• you can't know if a command doesn't output anything or not;
• there's no way to check if stdout is ready to be read or not.

The pr.Read(dest) method will block the code flow until something is read from stdout. As said, the goal is to read sequentially (without using a go routine and/or an infinite loop). This means that if we send a cd command the func end is never reached.

Setting the non-block flag through unix.SetNonblock on stdout file descriptor seems to solve the above issue but you can't know prior if it's ready or not and an error saying "resource temporary not available" is returned from .Read call.

Answer 1

As Cerise Limón mentioned go functions whould be the way to go here, since these sorts of interactive scripting exercises are traditionally done with expect.

You can wrap the the parrellel execution into a library to it might still look like sequencial code, so this might be helpful: https://github.com/ThomasRooney/gexpect

From the readme:

child, err := gexpect.Spawn("python")
if err != nil { panic(err) }
child.Expect(">>>")
child.SendLine("print 'Hello World'")
child.Interact()
child.Close()