update for containerd vendor changes

Signed-off-by: Mike Brown <brownwm@us.ibm.com>

vendor/github.com/urfave/cli/flag.go

@@ -3,6 +3,7 @@ package cli
 import (
 	"flag"
 	"fmt"
+	"io/ioutil"
 	"reflect"
 	"runtime"
 	"strconv"
@@ -45,6 +46,10 @@ var FlagNamePrefixer FlagNamePrefixFunc = prefixedNames
 // details. This is used by the default FlagStringer.
 var FlagEnvHinter FlagEnvHintFunc = withEnvHint
 
+// FlagFileHinter annotates flag help message with the environment variable
+// details. This is used by the default FlagStringer.
+var FlagFileHinter FlagFileHintFunc = withFileHint
+
 // FlagsByName is a slice of Flag.
 type FlagsByName []Flag
 
@@ -53,7 +58,7 @@ func (f FlagsByName) Len() int {
 }
 
 func (f FlagsByName) Less(i, j int) bool {
-	return f[i].GetName() < f[j].GetName()
+	return lexicographicLess(f[i].GetName(), f[j].GetName())
 }
 
 func (f FlagsByName) Swap(i, j int) {
@@ -70,6 +75,29 @@ type Flag interface {
 	GetName() string
 }
 
+// RequiredFlag is an interface that allows us to mark flags as required
+// it allows flags required flags to be backwards compatible with the Flag interface
+type RequiredFlag interface {
+	Flag
+
+	IsRequired() bool
+}
+
+// DocGenerationFlag is an interface that allows documentation generation for the flag
+type DocGenerationFlag interface {
+	Flag
+
+	// TakesValue returns true of the flag takes a value, otherwise false
+	TakesValue() bool
+
+	// GetUsage returns the usage string for the flag
+	GetUsage() string
+
+	// GetValue returns the flags value as string representation and an empty
+	// string if the flag takes no value at all.
+	GetValue() string
+}
+
 // errorableFlag is an interface that allows us to return errors during apply
 // it allows flags defined in this library to return errors in a fashion backwards compatible
 // TODO remove in v2 and modify the existing Flag interface to return errors
@@ -92,6 +120,7 @@ func flagSet(name string, flags []Flag) (*flag.FlagSet, error) {
 			f.Apply(set)
 		}
 	}
+	set.SetOutput(ioutil.Discard)
 	return set, nil
 }
 
@@ -113,22 +142,16 @@ type Generic interface {
 // provided by the user for parsing by the flag
 // Ignores parsing errors
 func (f GenericFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError takes the flagset and calls Set on the generic flag with the value
 // provided by the user for parsing by the flag
 func (f GenericFlag) ApplyWithError(set *flag.FlagSet) error {
 	val := f.Value
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				if err := val.Set(envVal); err != nil {
-					return fmt.Errorf("could not parse %s as value for flag %s: %s", envVal, f.Name, err)
-				}
-				break
-			}
+	if fileEnvVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		if err := val.Set(fileEnvVal); err != nil {
+			return fmt.Errorf("could not parse %s as value for flag %s: %s", fileEnvVal, f.Name, err)
 		}
 	}
 
@@ -166,26 +189,24 @@ func (f *StringSlice) Get() interface{} {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f StringSliceFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f StringSliceFlag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				newVal := &StringSlice{}
-				for _, s := range strings.Split(envVal, ",") {
-					s = strings.TrimSpace(s)
-					if err := newVal.Set(s); err != nil {
-						return fmt.Errorf("could not parse %s as string value for flag %s: %s", envVal, f.Name, err)
-					}
-				}
-				f.Value = newVal
-				break
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		newVal := &StringSlice{}
+		for _, s := range strings.Split(envVal, ",") {
+			s = strings.TrimSpace(s)
+			if err := newVal.Set(s); err != nil {
+				return fmt.Errorf("could not parse %s as string value for flag %s: %s", envVal, f.Name, err)
 			}
 		}
+		if f.Value == nil {
+			f.Value = newVal
+		} else {
+			*f.Value = *newVal
+		}
 	}
 
 	eachName(f.Name, func(name string) {
@@ -229,26 +250,24 @@ func (f *IntSlice) Get() interface{} {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f IntSliceFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f IntSliceFlag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				newVal := &IntSlice{}
-				for _, s := range strings.Split(envVal, ",") {
-					s = strings.TrimSpace(s)
-					if err := newVal.Set(s); err != nil {
-						return fmt.Errorf("could not parse %s as int slice value for flag %s: %s", envVal, f.Name, err)
-					}
-				}
-				f.Value = newVal
-				break
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		newVal := &IntSlice{}
+		for _, s := range strings.Split(envVal, ",") {
+			s = strings.TrimSpace(s)
+			if err := newVal.Set(s); err != nil {
+				return fmt.Errorf("could not parse %s as int slice value for flag %s: %s", envVal, f.Name, err)
 			}
 		}
+		if f.Value == nil {
+			f.Value = newVal
+		} else {
+			*f.Value = *newVal
+		}
 	}
 
 	eachName(f.Name, func(name string) {
@@ -292,26 +311,24 @@ func (f *Int64Slice) Get() interface{} {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f Int64SliceFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f Int64SliceFlag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				newVal := &Int64Slice{}
-				for _, s := range strings.Split(envVal, ",") {
-					s = strings.TrimSpace(s)
-					if err := newVal.Set(s); err != nil {
-						return fmt.Errorf("could not parse %s as int64 slice value for flag %s: %s", envVal, f.Name, err)
-					}
-				}
-				f.Value = newVal
-				break
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		newVal := &Int64Slice{}
+		for _, s := range strings.Split(envVal, ",") {
+			s = strings.TrimSpace(s)
+			if err := newVal.Set(s); err != nil {
+				return fmt.Errorf("could not parse %s as int64 slice value for flag %s: %s", envVal, f.Name, err)
 			}
 		}
+		if f.Value == nil {
+			f.Value = newVal
+		} else {
+			*f.Value = *newVal
+		}
 	}
 
 	eachName(f.Name, func(name string) {
@@ -326,29 +343,21 @@ func (f Int64SliceFlag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f BoolFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f BoolFlag) ApplyWithError(set *flag.FlagSet) error {
 	val := false
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				if envVal == "" {
-					val = false
-					break
-				}
-
-				envValBool, err := strconv.ParseBool(envVal)
-				if err != nil {
-					return fmt.Errorf("could not parse %s as bool value for flag %s: %s", envVal, f.Name, err)
-				}
-
-				val = envValBool
-				break
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		if envVal == "" {
+			val = false
+		} else {
+			envValBool, err := strconv.ParseBool(envVal)
+			if err != nil {
+				return fmt.Errorf("could not parse %s as bool value for flag %s: %s", envVal, f.Name, err)
 			}
+			val = envValBool
 		}
 	}
 
@@ -366,29 +375,22 @@ func (f BoolFlag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f BoolTFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f BoolTFlag) ApplyWithError(set *flag.FlagSet) error {
 	val := true
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				if envVal == "" {
-					val = false
-					break
-				}
 
-				envValBool, err := strconv.ParseBool(envVal)
-				if err != nil {
-					return fmt.Errorf("could not parse %s as bool value for flag %s: %s", envVal, f.Name, err)
-				}
-
-				val = envValBool
-				break
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		if envVal == "" {
+			val = false
+		} else {
+			envValBool, err := strconv.ParseBool(envVal)
+			if err != nil {
+				return fmt.Errorf("could not parse %s as bool value for flag %s: %s", envVal, f.Name, err)
 			}
+			val = envValBool
 		}
 	}
 
@@ -406,19 +408,13 @@ func (f BoolTFlag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f StringFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f StringFlag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				f.Value = envVal
-				break
-			}
-		}
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		f.Value = envVal
 	}
 
 	eachName(f.Name, func(name string) {
@@ -435,23 +431,17 @@ func (f StringFlag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f IntFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f IntFlag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				envValInt, err := strconv.ParseInt(envVal, 0, 64)
-				if err != nil {
-					return fmt.Errorf("could not parse %s as int value for flag %s: %s", envVal, f.Name, err)
-				}
-				f.Value = int(envValInt)
-				break
-			}
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		envValInt, err := strconv.ParseInt(envVal, 0, 64)
+		if err != nil {
+			return fmt.Errorf("could not parse %s as int value for flag %s: %s", envVal, f.Name, err)
 		}
+		f.Value = int(envValInt)
 	}
 
 	eachName(f.Name, func(name string) {
@@ -468,24 +458,18 @@ func (f IntFlag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f Int64Flag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f Int64Flag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				envValInt, err := strconv.ParseInt(envVal, 0, 64)
-				if err != nil {
-					return fmt.Errorf("could not parse %s as int value for flag %s: %s", envVal, f.Name, err)
-				}
-
-				f.Value = envValInt
-				break
-			}
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		envValInt, err := strconv.ParseInt(envVal, 0, 64)
+		if err != nil {
+			return fmt.Errorf("could not parse %s as int value for flag %s: %s", envVal, f.Name, err)
 		}
+
+		f.Value = envValInt
 	}
 
 	eachName(f.Name, func(name string) {
@@ -502,24 +486,18 @@ func (f Int64Flag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f UintFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f UintFlag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				envValInt, err := strconv.ParseUint(envVal, 0, 64)
-				if err != nil {
-					return fmt.Errorf("could not parse %s as uint value for flag %s: %s", envVal, f.Name, err)
-				}
-
-				f.Value = uint(envValInt)
-				break
-			}
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		envValInt, err := strconv.ParseUint(envVal, 0, 64)
+		if err != nil {
+			return fmt.Errorf("could not parse %s as uint value for flag %s: %s", envVal, f.Name, err)
 		}
+
+		f.Value = uint(envValInt)
 	}
 
 	eachName(f.Name, func(name string) {
@@ -536,24 +514,18 @@ func (f UintFlag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f Uint64Flag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f Uint64Flag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				envValInt, err := strconv.ParseUint(envVal, 0, 64)
-				if err != nil {
-					return fmt.Errorf("could not parse %s as uint64 value for flag %s: %s", envVal, f.Name, err)
-				}
-
-				f.Value = uint64(envValInt)
-				break
-			}
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		envValInt, err := strconv.ParseUint(envVal, 0, 64)
+		if err != nil {
+			return fmt.Errorf("could not parse %s as uint64 value for flag %s: %s", envVal, f.Name, err)
 		}
+
+		f.Value = envValInt
 	}
 
 	eachName(f.Name, func(name string) {
@@ -570,24 +542,18 @@ func (f Uint64Flag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f DurationFlag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f DurationFlag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				envValDuration, err := time.ParseDuration(envVal)
-				if err != nil {
-					return fmt.Errorf("could not parse %s as duration for flag %s: %s", envVal, f.Name, err)
-				}
-
-				f.Value = envValDuration
-				break
-			}
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		envValDuration, err := time.ParseDuration(envVal)
+		if err != nil {
+			return fmt.Errorf("could not parse %s as duration for flag %s: %s", envVal, f.Name, err)
 		}
+
+		f.Value = envValDuration
 	}
 
 	eachName(f.Name, func(name string) {
@@ -604,24 +570,18 @@ func (f DurationFlag) ApplyWithError(set *flag.FlagSet) error {
 // Apply populates the flag given the flag set and environment
 // Ignores errors
 func (f Float64Flag) Apply(set *flag.FlagSet) {
-	f.ApplyWithError(set)
+	_ = f.ApplyWithError(set)
 }
 
 // ApplyWithError populates the flag given the flag set and environment
 func (f Float64Flag) ApplyWithError(set *flag.FlagSet) error {
-	if f.EnvVar != "" {
-		for _, envVar := range strings.Split(f.EnvVar, ",") {
-			envVar = strings.TrimSpace(envVar)
-			if envVal, ok := syscall.Getenv(envVar); ok {
-				envValFloat, err := strconv.ParseFloat(envVal, 10)
-				if err != nil {
-					return fmt.Errorf("could not parse %s as float64 value for flag %s: %s", envVal, f.Name, err)
-				}
-
-				f.Value = float64(envValFloat)
-				break
-			}
+	if envVal, ok := flagFromFileEnv(f.FilePath, f.EnvVar); ok {
+		envValFloat, err := strconv.ParseFloat(envVal, 10)
+		if err != nil {
+			return fmt.Errorf("could not parse %s as float64 value for flag %s: %s", envVal, f.Name, err)
 		}
+
+		f.Value = envValFloat
 	}
 
 	eachName(f.Name, func(name string) {
@@ -636,11 +596,11 @@ func (f Float64Flag) ApplyWithError(set *flag.FlagSet) error {
 }
 
 func visibleFlags(fl []Flag) []Flag {
-	visible := []Flag{}
-	for _, flag := range fl {
-		field := flagValue(flag).FieldByName("Hidden")
+	var visible []Flag
+	for _, f := range fl {
+		field := flagValue(f).FieldByName("Hidden")
 		if !field.IsValid() || !field.Bool() {
-			visible = append(visible, flag)
+			visible = append(visible, f)
 		}
 	}
 	return visible
@@ -700,11 +660,19 @@ func withEnvHint(envVar, str string) string {
 			suffix = "%"
 			sep = "%, %"
 		}
-		envText = fmt.Sprintf(" [%s%s%s]", prefix, strings.Join(strings.Split(envVar, ","), sep), suffix)
+		envText = " [" + prefix + strings.Join(strings.Split(envVar, ","), sep) + suffix + "]"
 	}
 	return str + envText
 }
 
+func withFileHint(filePath, str string) string {
+	fileText := ""
+	if filePath != "" {
+		fileText = fmt.Sprintf(" [%s]", filePath)
+	}
+	return str + fileText
+}
+
 func flagValue(f Flag) reflect.Value {
 	fv := reflect.ValueOf(f)
 	for fv.Kind() == reflect.Ptr {
@@ -718,14 +686,29 @@ func stringifyFlag(f Flag) string {
 
 	switch f.(type) {
 	case IntSliceFlag:
-		return FlagEnvHinter(fv.FieldByName("EnvVar").String(),
-			stringifyIntSliceFlag(f.(IntSliceFlag)))
+		return FlagFileHinter(
+			fv.FieldByName("FilePath").String(),
+			FlagEnvHinter(
+				fv.FieldByName("EnvVar").String(),
+				stringifyIntSliceFlag(f.(IntSliceFlag)),
+			),
+		)
 	case Int64SliceFlag:
-		return FlagEnvHinter(fv.FieldByName("EnvVar").String(),
-			stringifyInt64SliceFlag(f.(Int64SliceFlag)))
+		return FlagFileHinter(
+			fv.FieldByName("FilePath").String(),
+			FlagEnvHinter(
+				fv.FieldByName("EnvVar").String(),
+				stringifyInt64SliceFlag(f.(Int64SliceFlag)),
+			),
+		)
 	case StringSliceFlag:
-		return FlagEnvHinter(fv.FieldByName("EnvVar").String(),
-			stringifyStringSliceFlag(f.(StringSliceFlag)))
+		return FlagFileHinter(
+			fv.FieldByName("FilePath").String(),
+			FlagEnvHinter(
+				fv.FieldByName("EnvVar").String(),
+				stringifyStringSliceFlag(f.(StringSliceFlag)),
+			),
+		)
 	}
 
 	placeholder, usage := unquoteUsage(fv.FieldByName("Usage").String())
@@ -750,17 +733,22 @@ func stringifyFlag(f Flag) string {
 		placeholder = defaultPlaceholder
 	}
 
-	usageWithDefault := strings.TrimSpace(fmt.Sprintf("%s%s", usage, defaultValueString))
+	usageWithDefault := strings.TrimSpace(usage + defaultValueString)
 
-	return FlagEnvHinter(fv.FieldByName("EnvVar").String(),
-		fmt.Sprintf("%s\t%s", FlagNamePrefixer(fv.FieldByName("Name").String(), placeholder), usageWithDefault))
+	return FlagFileHinter(
+		fv.FieldByName("FilePath").String(),
+		FlagEnvHinter(
+			fv.FieldByName("EnvVar").String(),
+			FlagNamePrefixer(fv.FieldByName("Name").String(), placeholder)+"\t"+usageWithDefault,
+		),
+	)
 }
 
 func stringifyIntSliceFlag(f IntSliceFlag) string {
-	defaultVals := []string{}
+	var defaultVals []string
 	if f.Value != nil && len(f.Value.Value()) > 0 {
 		for _, i := range f.Value.Value() {
-			defaultVals = append(defaultVals, fmt.Sprintf("%d", i))
+			defaultVals = append(defaultVals, strconv.Itoa(i))
 		}
 	}
 
@@ -768,10 +756,10 @@ func stringifyIntSliceFlag(f IntSliceFlag) string {
 }
 
 func stringifyInt64SliceFlag(f Int64SliceFlag) string {
-	defaultVals := []string{}
+	var defaultVals []string
 	if f.Value != nil && len(f.Value.Value()) > 0 {
 		for _, i := range f.Value.Value() {
-			defaultVals = append(defaultVals, fmt.Sprintf("%d", i))
+			defaultVals = append(defaultVals, strconv.FormatInt(i, 10))
 		}
 	}
 
@@ -779,11 +767,11 @@ func stringifyInt64SliceFlag(f Int64SliceFlag) string {
 }
 
 func stringifyStringSliceFlag(f StringSliceFlag) string {
-	defaultVals := []string{}
+	var defaultVals []string
 	if f.Value != nil && len(f.Value.Value()) > 0 {
 		for _, s := range f.Value.Value() {
 			if len(s) > 0 {
-				defaultVals = append(defaultVals, fmt.Sprintf("%q", s))
+				defaultVals = append(defaultVals, strconv.Quote(s))
 			}
 		}
 	}
@@ -802,6 +790,21 @@ func stringifySliceFlag(usage, name string, defaultVals []string) string {
 		defaultVal = fmt.Sprintf(" (default: %s)", strings.Join(defaultVals, ", "))
 	}
 
-	usageWithDefault := strings.TrimSpace(fmt.Sprintf("%s%s", usage, defaultVal))
-	return fmt.Sprintf("%s\t%s", FlagNamePrefixer(name, placeholder), usageWithDefault)
+	usageWithDefault := strings.TrimSpace(usage + defaultVal)
+	return FlagNamePrefixer(name, placeholder) + "\t" + usageWithDefault
+}
+
+func flagFromFileEnv(filePath, envName string) (val string, ok bool) {
+	for _, envVar := range strings.Split(envName, ",") {
+		envVar = strings.TrimSpace(envVar)
+		if envVal, ok := syscall.Getenv(envVar); ok {
+			return envVal, true
+		}
+	}
+	for _, fileVar := range strings.Split(filePath, ",") {
+		if data, err := ioutil.ReadFile(fileVar); err == nil {
+			return string(data), true
+		}
+	}
+	return "", false
 }