envflag.go
func StringVar(p *string, name string, value string, usage string) {
	EnvironmentFlags.StringVar(p, name, value, usage)
}
func StringVar(p *string, name string, value string, usage string) {
	EnvironmentFlags.StringVar(p, name, value, usage)
}
// StringVar defines a string flag with specified name, default value,
// and usage string.  The argument p points to a string variable in
// which to store the value of the flag.