How to use the kas.libcmds.Command function in kas

macro.add(ReposApplyPatches())

        macro.add(WriteBBConfig())

        # Build
        macro.add(BuildCommand(args.extra_bitbake_args))

        if 'SSH_PRIVATE_KEY' in os.environ:
            macro.add(CleanupSSHAgent())

        macro.run(ctx, args.skip)

        return True


class BuildCommand(Command):
    """
        Implements the bitbake build step.
    """

    def __init__(self, extra_bitbake_args):
        super().__init__()
        self.extra_bitbake_args = extra_bitbake_args

    def __str__(self):
        return 'build'

    def execute(self, ctx):
        """
            Executes the bitbake build command.
        """
        # Start bitbake build of image

command.execute(ctx)


class Command:
    """
        An abstract class that defines the interface of a command.
    """

    def execute(self, ctx):
        """
            This method executes the command.
        """
        pass


class Loop(Command):
    """
        A class that defines a set of commands as a loop.
    """
    def __init__(self, name):
        self.commands = []
        self.name = name

    def __str__(self):
        return self.name

    def add(self, command):
        """
            Appends a command to the loop.
        """
        self.commands.append(command)

def _write_local_conf(ctx):
            filename = ctx.build_dir + '/conf/local.conf'
            with open(filename, 'w') as fds:
                fds.write(ctx.config.get_local_conf_header())
                fds.write('MACHINE ??= "{}"\n'.format(
                    ctx.config.get_machine()))
                fds.write('DISTRO ??= "{}"\n'.format(
                    ctx.config.get_distro()))
                fds.write('BBMULTICONFIG ?= "{}"\n'.format(
                    ctx.config.get_multiconfig()))

        _write_bblayers_conf(ctx)
        _write_local_conf(ctx)


class ReposFetch(Command):
    """
        Fetches repositories defined in the configuration
    """

    def __str__(self):
        return 'repos_fetch'

    def execute(self, ctx):
        repos_fetch(ctx.config.get_repos())


class ReposApplyPatches(Command):
    """
        Applies the patches defined in the configuration to the repositories.
    """

ssh_no_host_key_check()


class CleanupSSHAgent(Command):
    """
        Removes all the identities and stops the ssh-agent instance.
    """

    def __str__(self):
        return 'cleanup_ssh_agent'

    def execute(self, ctx):
        ssh_cleanup_agent()


class SetupEnviron(Command):
    """
        Sets up the kas environment.
    """

    def __str__(self):
        return 'setup_environ'

    def execute(self, ctx):
        ctx.environ.update(get_build_environ())


class WriteBBConfig(Command):
    """
        Writes bitbake configuration files into the build directory.
    """

class ReposCheckout(Command):
    """
        Ensures that the right revision of each repo is checked out.
    """

    def __str__(self):
        return 'repos_checkout'

    def execute(self, ctx):
        for repo in ctx.config.get_repos():
            repo.checkout()


class InitSetupRepos(Command):
    """
        Prepares setting up repos including the include logic
    """

    def __str__(self):
        return 'init_setup_repos'

    def execute(self, ctx):
        ctx.missing_repo_names = ctx.config.find_missing_repos()
        ctx.missing_repo_names_old = None


class SetupReposStep(Command):
    """
        Single step of the checkout repos loop
    """

class InitSetupRepos(Command):
    """
        Prepares setting up repos including the include logic
    """

    def __str__(self):
        return 'init_setup_repos'

    def execute(self, ctx):
        ctx.missing_repo_names = ctx.config.find_missing_repos()
        ctx.missing_repo_names_old = None


class SetupReposStep(Command):
    """
        Single step of the checkout repos loop
    """

    def __str__(self):
        return 'setup_repos_step'

    def execute(self, ctx):
        """ TODO refactor protected-access """
        if not ctx.missing_repo_names:
            return False

        if ctx.missing_repo_names == ctx.missing_repo_names_old:
            raise IncludeException('Could not fetch all repos needed by '
                                   'includes.')

class SetupDir(Command):
    """
        Creates the build directory.
    """

    def __str__(self):
        return 'setup_dir'

    def execute(self, ctx):
        os.chdir(ctx.kas_work_dir)
        if not os.path.exists(ctx.build_dir):
            os.mkdir(ctx.build_dir)


class SetupSSHAgent(Command):
    """
        Sets up the ssh agent configuration.
    """

    def __str__(self):
        return 'setup_ssh_agent'

    def execute(self, ctx):
        ssh_setup_agent()
        ssh_no_host_key_check()


class CleanupSSHAgent(Command):
    """
        Removes all the identities and stops the ssh-agent instance.
    """

class SetupSSHAgent(Command):
    """
        Sets up the ssh agent configuration.
    """

    def __str__(self):
        return 'setup_ssh_agent'

    def execute(self, ctx):
        ssh_setup_agent()
        ssh_no_host_key_check()


class CleanupSSHAgent(Command):
    """
        Removes all the identities and stops the ssh-agent instance.
    """

    def __str__(self):
        return 'cleanup_ssh_agent'

    def execute(self, ctx):
        ssh_cleanup_agent()


class SetupEnviron(Command):
    """
        Sets up the kas environment.
    """

if not args.keep_config_unchanged:
            macro.add(ReposApplyPatches())
            macro.add(WriteBBConfig())

        # Shell
        macro.add(ShellCommand(args.command))

        if 'SSH_PRIVATE_KEY' in os.environ:
            macro.add(CleanupSSHAgent())

        macro.run(ctx, args.skip)

        return True


class ShellCommand(Command):
    """
        This class implements the command that starts a shell.
    """

    def __init__(self, cmd):
        super().__init__()
        self.cmd = []
        if cmd:
            self.cmd = cmd

    def __str__(self):
        return 'shell'

    def execute(self, ctx):
        cmd = [ctx.environ.get('SHELL', '/bin/sh')]
        if self.cmd:

_write_local_conf(ctx)


class ReposFetch(Command):
    """
        Fetches repositories defined in the configuration
    """

    def __str__(self):
        return 'repos_fetch'

    def execute(self, ctx):
        repos_fetch(ctx.config.get_repos())


class ReposApplyPatches(Command):
    """
        Applies the patches defined in the configuration to the repositories.
    """

    def __str__(self):
        return 'repos_apply_patches'

    def execute(self, ctx):
        repos_apply_patches(ctx.config.get_repos())


class ReposCheckout(Command):
    """
        Ensures that the right revision of each repo is checked out.
    """