Make transform*, --info-command, and execute-silent cancellable

Users can press CTRL-C after 1 second to terminate the command.

Close #3883

src/util/util.go

@@ -144,12 +144,22 @@ func IsTty(file *os.File) bool {
 	return isatty.IsTerminal(fd) || isatty.IsCygwinTerminal(fd)
 }
 
+// RunOnce runs the given function only once
+func RunOnce(f func()) func() {
+	once := Once(true)
+	return func() {
+		if once() {
+			f()
+		}
+	}
+}
+
 // Once returns a function that returns the specified boolean value only once
 func Once(nextResponse bool) func() bool {
 	state := nextResponse
 	return func() bool {
 		prevState := state
-		state = false
+		state = !nextResponse
 		return prevState
 	}
 }

src/util/util_test.go

@@ -137,8 +137,11 @@ func TestOnce(t *testing.T) {
 	if o() {
 		t.Error("Expected: false")
 	}
-	if o() {
-		t.Error("Expected: false")
+	if !o() {
+		t.Error("Expected: true")
+	}
+	if !o() {
+		t.Error("Expected: true")
 	}
 
 	o = Once(true)
@@ -148,6 +151,9 @@ func TestOnce(t *testing.T) {
 	if o() {
 		t.Error("Expected: false")
 	}
+	if o() {
+		t.Error("Expected: false")
+	}
 }
 
 func TestRunesWidth(t *testing.T) {