Add input scanning utilities

pkg/util/inpututil/scan.go

+package inpututil
+
+import (
+	"fmt"
+	"strings"
+)
+
+var (
+	booleanValues = map[string]bool{
+		"y":   true,
+		"yes": true,
+		"yup": true,
+
+		"n":    false,
+		"no":   false,
+		"nope": false,
+	}
+)
+
+func ScanYesOrNo(msg string, def bool) (bool, error) {
+	var choices string
+	if def {
+		choices = "Y/n"
+	} else {
+		choices = "y/N"
+	}
+
+	fmt.Print(msg, " ", choices, " ")
+
+	var choice string
+	_, err := fmt.Scanf("%s", &choice)
+	if err != nil {
+		return def, err
+	}
+
+	switch val, ok := booleanValues[strings.ToLower(choice)]; {
+	case ok:
+		return val, nil
+	case choice == "":
+		return def, nil
+	}
+
+	return def, fmt.Errorf("unrecognized choice %#q", choice)
+}
+
+func ScanValue(msg string) (string, error) {
+	fmt.Print(msg)
+
+	var value string
+	_, err := fmt.Scanf("%s", &value)
+	if err != nil {
+		return "", err
+	}
+
+	return value, nil
+}