concurrent exec: single producer, multiple consumer

exec.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"io/ioutil"
	"os"
	"os/exec"
	"strings"
	"sync"
)

func main() {

	// Flags for output
	commandFlag := flag.String("command", "", "what command to send to shell")
	hostsFlag := flag.String("hosts", "", "the file with hosts")
	conFlag := flag.Int("threads", 8, "level of concurrent operations")

	// Parse flags
	flag.Parse()

	switch {
	case *commandFlag == "":
		fmt.Fprintln(os.Stderr, "command required")
		os.Exit(1)
	case *hostsFlag == "":
		fmt.Fprintln(os.Stderr, "host file required")
		os.Exit(1)
	}

	// initialize waitgroup
	var wg sync.WaitGroup

	// make channel for the commands
	tasks := make(chan *exec.Cmd, 64)

	// create buffer for output
	out := bufio.NewWriter(os.Stdout)

	// for loop that will make x routines set from threads flag
	for i := 0; i < *conFlag; i++ {
		wg.Add(1)
		go func() {
			// range through tasks channel
			for cmd := range tasks {

				// execute command and get output
				cmdout, err := cmd.Output()
				if err != nil {
					fmt.Fprintln(os.Stderr, err)
					return
				}

				// print to buffer
				fmt.Fprintf(out, "%s", cmdout)
				out.Flush()

			}

			wg.Done()

		}()
	}

	// read file
	file, err := ioutil.ReadFile(*hostsFlag)
	if err != nil {
		fmt.Fprintln(os.Stderr, "problem opening file")
		os.Exit(1)
	}

	// trim last newline from file
	h := strings.TrimSpace(string(file))

	// split on newlines into slice
	hosts := strings.Split(h, "\n")

	// range over hostnames in slice
	for _, host := range hosts {

		tasks <- exec.Command("mco", "shell", "--publish_timeout=2", "-t2", "-I", host, *commandFlag)

	}

	// close channel
	close(tasks)

	// wait until routines are done
	wg.Wait()

}