// A CommandError describes an error resulting from attempting to execute a
// specific command.
type CommandError struct {
	File string
	Line int
	Op   string
	Args []string
	Err  error
}

func cmdError(cmd *command, err error) *CommandError {
	return &CommandError{
		File: cmd.file,
		Line: cmd.line,
		Op:   cmd.name,
		Args: cmd.args,
		Err:  err,
	}
}

func (e *CommandError) Error() string {