ExpandEnv is like os.ExpandEnv but supports 'pseudo' environment variables that have OS specific handling as follows: On Windows $HOME and $PATH are replaced by and $HOMEDRIVE:\\$HOMEPATH and $Path respectively.

ParseFlagTag parses the supplied string into a flag name, default literal value and description components.

RegisterFlagsInStruct will selectively register fields in the supplied struct as flags of the appropriate type with the supplied flag.FlagSet.