go-deb/cmd.go

package main

// this is a simplified interaction with the excellent
// go-cmd/cmd package to work 'shell' like.

// in all cases here, STDERR -> STDOUT
// If you want the output from whatever you run
// to be captured like it appears when you see it
// on the command line, this is what this tries to do

/*
	if r := shell.Run([]{"ping", "-c", "3", "localhost"}); r.Error == nil {
		if r.Exit == 0 {
			log.Println("ran ok")
		} else {
			log.Println("ran")
		}
		// all stdout/stderr captured in r.Stdout
	}
*/

import (
	"errors"
	"fmt"
	"time"

	"github.com/go-cmd/cmd"
	"go.wit.com/log"
)

func Run(args []string) cmd.Status {
	return PwdRun("", args)
}

// absolutely doesn't echo anything
func PwdRunQuiet(pwd string, args []string) cmd.Status {
	var arg0 string
	var argx []string
	// Check if the slice has at least one element (the command name)
	if len(args) == 0 {
		var s cmd.Status
		s.Error = errors.New("Error: Command slice is empty.")
		return s
	}
	if len(args) == 1 {
		// Pass the first element as the command, and the rest as variadic arguments
		arg0 = args[0]
	} else {
		arg0 = args[0]
		argx = args[1:]
	}

	// Start a long-running process, capture stdout and stderr
	findCmd := cmd.NewCmd(arg0, argx...)
	if pwd != "" {
		findCmd.Dir = pwd
	}
	statusChan := findCmd.Start() // non-blocking

	ticker := time.NewTicker(2 * time.Second)

	// this is interesting, maybe useful, but wierd, but neat. interesting even
	// Print last line of stdout every 2s
	go func() {
		for range ticker.C {
			status := findCmd.Status()
			n := len(status.Stdout)
			if n != 0 {
				fmt.Println(status.Stdout[n-1])
			}
		}
	}()

	// Stop command after 1 hour
	go func() {
		<-time.After(1 * time.Hour)
		findCmd.Stop()
	}()

	// Check if command is done
	select {
	case finalStatus := <-statusChan:
		log.Info("finalStatus =", finalStatus.Exit, finalStatus.Error)
		return finalStatus
		// done
	default:
		// no, still running
	}

	// Block waiting for command to exit, be stopped, or be killed
	finalStatus := <-statusChan
	return finalStatus
}

func blah(cmd []string) {
	r := Run(cmd)
	log.Info("cmd =", r.Cmd)
	log.Info("complete =", r.Complete)
	log.Info("exit =", r.Exit)
	log.Info("err =", r.Error)
	log.Info("len(stdout+stderr) =", len(r.Stdout))
}

// run these to see confirm the sytem behaves as expected
func RunTest() {
	blah([]string{"ping", "-c", "3", "localhost"})
	blah([]string{"exit", "0"})
	blah([]string{"exit", "-1"})
	blah([]string{"true"})
	blah([]string{"false"})
	blah([]string{"grep", "root", "/etc/", "/proc/cmdline", "/usr/bin/chmod"})
	blah([]string{"grep", "root", "/proc/cmdline"})
	fmt.Sprint("blahdone")
}

// sets the exec dir if it's sent
// combines stdout and stderr
// echo's output
func PwdRun(pwd string, args []string) cmd.Status {
	var save []string // combined stdout & stderr
	var arg0 string
	var argx []string
	// Check if the slice has at least one element (the command name)
	if len(args) == 0 {
		var s cmd.Status
		s.Error = errors.New("Error: Command slice is empty.")
		return s
	}
	if len(args) == 1 {
		// Pass the first element as the command, and the rest as variadic arguments
		arg0 = args[0]
	} else {
		arg0 = args[0]
		argx = args[1:]
	}

	// Disable output buffering, enable streaming
	cmdOptions := cmd.Options{
		Buffered:  false,
		Streaming: true,
	}

	// Create Cmd with options
	envCmd := cmd.NewCmdOptions(cmdOptions, arg0, argx...)
	if pwd != "" {
		envCmd.Dir = pwd
	}

	// Print STDOUT and STDERR lines streaming from Cmd
	doneChan := make(chan struct{})
	go func() {
		defer close(doneChan)
		// Done when both channels have been closed
		// https://dave.cheney.net/2013/04/30/curious-channels
		for envCmd.Stdout != nil || envCmd.Stderr != nil {
			select {
			case line, open := <-envCmd.Stdout:
				if !open {
					envCmd.Stdout = nil
					continue
				}
				save = append(save, line)
				fmt.Println(line)
			case line, open := <-envCmd.Stderr:
				if !open {
					envCmd.Stderr = nil
					continue
				}
				save = append(save, line)
				fmt.Println(line)
			}
		}
	}()

	// Run and wait for Cmd to return, discard Status
	<-envCmd.Start()

	// Wait for goroutine to print everything
	<-doneChan

	s := envCmd.Status()
	s.Stdout = save
	return s
}