Check if exec.Cmd is done running in Go

Question

I'm trying to check if an exec.Cmd is running in these scenarios:

1. Before I actually started the command
2. After the command has started, but before it finished
3. After the command has finished

This will allow me to kill this command if it is running so that I can start it again with different parameters.

A simple use case below:

c := exec.Command("omxplayer", "video.mp4")
s, _ := c.StdinPipe() // use the pipe to send the "q" string to quit omxplayer

log.Printf("Running (false): %v\n", checkRunning(c)) // prints false: command has not started yet
c.Start()
log.Printf("Running (true): %v\n", checkRunning(c)) // print true: command has started

time.AfterFunc(3*time.Second, func() {
  log.Println("about to quit process...")
  log.Printf("Running (true): %v\n", checkRunning(c)) // prints true: command still running at this point
  s.Write([]byte("q"))
})

log.Println("waiting for command to end")
log.Printf("Running (true): %v\n", checkRunning(c)) // prints true: command still running at this point
c.Wait()
log.Println("command should have ended by now")
log.Printf("Running (false): %v\n", checkRunning(c)) // prints false: command ended at this point

Here's the best that I could come up with:

func checkRunning(cmd *exec.Cmd) bool {
  if cmd == nil || cmd.ProcessState != nil && cmd.ProcessState.Exited() || cmd.Process == nil {
    return false
  }

  return true
}

It works for the use case above, but it seems overly complicated and I'm not sure how reliable it is.

Is there a better way?

Answer 1

Maybe run synchronously in a goroutine and put the result on a channel you can select on?

c := exec.Command("omxplayer", "video.mp4")
// setup pipes and such
ch := make(chan error)
go func(){
  ch <- c.Run()
}()
select{
  case err := <- ch:
    // done! check error
  case .... //timeouts, ticks or anything else
}

Answer 2

A slightly different approach to captncraig's answer that worked for me:

c := exec.Command("omxplayer", "video.mp4")
err := c.Start() // starts the specified command but does not wait for it to complete

// wait for the program to end in a goroutine
go func() {
  err := c.Wait()
  // logic to run once process finished. Send err in channel if necessary
}()