urfave/sflags

type HTTPConfig struct {
	Host    string        `desc:"HTTP host"`
	Port    int           `flag:"port p" desc:"some port"`
	SSL     bool          `env:"HTTP_SSL_VALUE"`
	Timeout time.Duration `flag:",deprecated,hidden"`
}

type Config struct {
	HTTP  HTTPConfig
	Stats StatsConfig
}

package main

import (
	"flag"
	"log"
	"time"

	"github.com/urfave/sflags/gen/gflag"
)

type httpConfig struct {
	Host    string `desc:"HTTP host"`
	Port    int
	SSL     bool
	Timeout time.Duration
}

type config struct {
	HTTP httpConfig
}

func main() {
	cfg := &config{
		HTTP: httpConfig{
			Host:    "127.0.0.1",
			Port:    6000,
			SSL:     false,
			Timeout: 15 * time.Second,
		},
	}
	err := gflag.ParseToDef(cfg)
	if err != nil {
		log.Fatalf("err: %v", err)
	}
	flag.Parse()
}

$ go run ./main.go --help
Usage of _obj/exe/main:
  -http-host value
    	HTTP host (default 127.0.0.1)
  -http-port value
    	 (default 6000)
  -http-ssl

  -http-timeout value
    	 (default 15s)
exit status 2

// Field is ignored by this package.
Field int `flag:"-"`

// Field appears in flags as "myName".
Field int `flag:"myName"`

// If this field is from nested struct, prefix from parent struct will be ingored.
Field int `flag:"~myName"`

// You can set short name for flags by providing it's value after a space
// Prefixes will not be applied for short names.
Field int `flag:"myName a"`

// this field will be removed from generated help text.
Field int `flag:",hidden"`

// this field will be marked as deprecated in generated help text
Field int `flag:",deprecated"`

Addr string `desc:"HTTP host"`

  -addr value
    	HTTP host (default 127.0.0.1)

SSL     bool          `env:"HTTP_SSL_VALUE"`

// DescTag sets custom description tag. It is "desc" by default.
func DescTag(val string)

// FlagTag sets custom flag tag. It is "flag" be default.
func FlagTag(val string)

// Prefix sets prefix that will be applied for all flags (if they are not marked as ~).
func Prefix(val string)

// EnvPrefix sets prefix that will be applied for all environment variables (if they are not marked as ~).
func EnvPrefix(val string)

// FlagDivider sets custom divider for flags. It is dash by default. e.g. "flag-name".
func FlagDivider(val string)

// EnvDivider sets custom divider for environment variables.
// It is underscore by default. e.g. "ENV_NAME".
func EnvDivider(val string)

// Validator sets validator function for flags.
// Check existed validators in sflags/validator package.
func Validator(val ValidateFunc)

// Set to false if you don't want anonymous structure fields to be flattened.
func Flatten(val bool)

// InheritHidden sets if fields should inherit the value of the hidden tag from parent structs.
func InheritHidden()

// InheritDeprecated sets if fields should inherit the value of the deprecated tag from parent structs.
func InheritDeprecated()