Only use stub when it is alive.

eval/eval.go

@@ -180,7 +180,7 @@ func (ev *Evaler) EvalInteractive(text string, n *parse.Chunk) error {
 	signal.Ignore(syscall.SIGTTIN)
 	signal.Ignore(syscall.SIGTTOU)
 	// XXX Should use fd of /dev/terminal instead of 0.
-	if ev.Stub != nil && sys.IsATTY(0) {
+	if ev.Stub != nil && ev.Stub.Alive() && sys.IsATTY(0) {
 		ev.Stub.SetTitle(summarize(text))
 		dir, err := os.Getwd()
 		if err != nil {

eval/externalcmd.go

@@ -59,7 +59,7 @@ func (e ExternalCmd) Call(ec *EvalCtx, argVals []Value) {
 	}
 
 	sys := syscall.SysProcAttr{}
-	if ec.Stub != nil {
+	if ec.Stub != nil && ec.Stub.Alive() {
 		sys.Setpgid = true
 		sys.Pgid = ec.Stub.Process().Pid
 	}

run/run.go

@@ -76,6 +76,10 @@ func Main() {
 		fmt.Println("failed to spawn stub:", err)
 	} else {
 		ev.Stub = stub
+		go func() {
+			<-stub.State()
+			fmt.Println("stub has died")
+		}()
 	}
 
 	if len(args) == 1 {

stub/stub.go

@@ -114,6 +114,16 @@ func (stub *Stub) State() <-chan struct{} {
 	return stub.statech
 }
 
+// Alive reports whether the stub is alive.
+func (stub *Stub) Alive() bool {
+	select {
+	case <-stub.statech:
+		return false
+	default:
+		return true
+	}
+}
+
 // relaySignals relays output of the stub to sigch, assuming that outputs
 // represent signal numbers.
 func relaySignals(reader io.Reader, sigch chan<- os.Signal) {