How to use the tern.utils.constants.shell function in tern

shell, _ = command_lib.get_image_shell(
        command_lib.get_base_listing(binary))
    if not shell:
        # add a warning notice for no shell in the command library
        logger.warning('No shell listing in command library. '
                       'Using default shell')
        no_shell_message = errors.no_shell_listing.format(
            binary=binary, default_shell=constants.shell)
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_command_lib, Notice(no_shell_message, 'warning'))
        # add a hint notice to add the shell to the command library
        add_shell_message = errors.no_listing_for_base_key.format(
            listing_key='shell')
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_command_lib, Notice(add_shell_message, 'hint'))
        shell = constants.shell

    return shell

shell, _ = command_lib.get_image_shell(
        command_lib.get_base_listing(binary))
    if not shell:
        # add a warning notice for no shell in the command library
        logger.warning('No shell listing in command library. '
                       'Using default shell')
        no_shell_message = errors.no_shell_listing.format(
            binary=binary, default_shell=constants.shell)
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_command_lib, Notice(no_shell_message, 'warning'))
        # add a hint notice to add the shell to the command library
        add_shell_message = errors.no_listing_for_base_key.format(
            listing_key='shell')
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_command_lib, Notice(add_shell_message, 'hint'))
        shell = constants.shell
    # only extract packages if there is a known binary and the layer is not
    # cached
    if binary:
        if not common.load_from_cache(image_obj.layers[0], redo):
            # Determine pacakge/os style from binary in the image layer
            common.get_os_style(image_obj.layers[0], binary)
            # get the packages of the first layer
            rootfs.prep_rootfs(target)
            common.add_base_packages(image_obj.layers[0], binary, shell)
            # unmount proc, sys and dev
            rootfs.undo_mount()
    else:
        logger.warning(errors.no_package_manager)
        # /etc/os-release may still be present even if binary is not
        common.get_os_style(image_obj.layers[0], None)
        image_obj.layers[0].origins.add_notice_to_origins(

# Determine pacakge/os style from binary in the image layer
            common.get_os_style(image_obj.layers[0], binary)
            # get the packages of the first layer
            rootfs.prep_rootfs(target)
            common.add_base_packages(image_obj.layers[0], binary, shell)
            # unmount proc, sys and dev
            rootfs.undo_mount()
    else:
        logger.warning(errors.no_package_manager)
        # /etc/os-release may still be present even if binary is not
        common.get_os_style(image_obj.layers[0], None)
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_first_layer, Notice(errors.no_package_manager, 'warning'))
        # no binary means there is no shell so set to default shell
        logger.warning('Unknown filesystem. Using default shell')
        shell = constants.shell
    # unmount the first layer
    rootfs.unmount_rootfs()
    # populate the master list with all packages found in the first layer
    for p in image_obj.layers[0].packages:
        master_list.append(p)
    # get packages for subsequent layers
    curr_layer = 1
    while curr_layer < len(image_obj.layers):
        if not common.load_from_cache(image_obj.layers[curr_layer], redo):
            # get commands that created the layer
            # for docker images this is retrieved from the image history
            command_list = dhelper.get_commands_from_history(
                image_obj.layers[curr_layer])
            if command_list:
                # mount diff layers from 0 till the current layer
                target = mount_overlay_fs(image_obj, curr_layer)

# find the binary by mounting the base layer
    target = rootfs.mount_base_layer(image_obj.layers[0].tar_file)
    binary = common.get_base_bin()
    # set up a notice origin referring to the base command library listing
    origin_command_lib = formats.invoking_base_commands
    # set up a notice origin for the first layer
    origin_first_layer = 'Layer: ' + image_obj.layers[0].fs_hash[:10]
    # find the shell to invoke commands in
    shell, _ = command_lib.get_image_shell(
        command_lib.get_base_listing(binary))
    if not shell:
        # add a warning notice for no shell in the command library
        logger.warning('No shell listing in command library. '
                       'Using default shell')
        no_shell_message = errors.no_shell_listing.format(
            binary=binary, default_shell=constants.shell)
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_command_lib, Notice(no_shell_message, 'warning'))
        # add a hint notice to add the shell to the command library
        add_shell_message = errors.no_listing_for_base_key.format(
            listing_key='shell')
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_command_lib, Notice(add_shell_message, 'hint'))
        shell = constants.shell
    # only extract packages if there is a known binary and the layer is not
    # cached
    if binary:
        if not common.load_from_cache(image_obj.layers[0], redo):
            # Determine pacakge/os style from binary in the image layer
            common.get_os_style(image_obj.layers[0], binary)
            # get the packages of the first layer
            rootfs.prep_rootfs(target)

rootfs.prep_rootfs(target)
                common.add_base_packages(image_obj.layers[0], binary, shell)
            except KeyboardInterrupt:
                logger.critical(errors.keyboard_interrupt)
                abort_analysis()
            # unmount proc, sys and dev
            rootfs.undo_mount()
    else:
        logger.warning(errors.no_package_manager)
        # /etc/os-release may still be present even if binary is not
        common.get_os_style(image_obj.layers[0], None)
        image_obj.layers[0].origins.add_notice_to_origins(
            origin_first_layer, Notice(errors.no_package_manager, 'warning'))
        # no binary means there is no shell so set to default shell
        logger.warning('Unknown filesystem. Using default shell')
        shell = constants.shell
    # unmount the first layer
    rootfs.unmount_rootfs()
    # populate the master list with all packages found in the first layer
    for p in image_obj.layers[0].packages:
        master_list.append(p)
    return shell

'info'))
    else:
        image_layer.origins.add_notice_to_origins(origin_layer, Notice(
            formats.no_created_by, 'warning'))
    origin_command_lib = formats.invoking_base_commands
    # find the binary
    listing = command_lib.get_base_listing(binary)
    if listing:
        # put info notice about what is going to be invoked
        snippet_msg = formats.invoke_for_base + '\n' + \
            content.print_base_invoke(binary)
        image_layer.origins.add_notice_to_origins(
            origin_layer, Notice(snippet_msg, 'info'))
        shell, _ = command_lib.get_image_shell(listing)
        if not shell:
            shell = constants.shell
        # get all the packages in the base layer
        pkg_dict, invoke_msg, warnings = collate_list_metadata(shell, listing)
        if invoke_msg:
            image_layer.origins.add_notice_to_origins(
                origin_layer, Notice(invoke_msg, 'error'))
        if warnings:
            image_layer.origins.add_notice_to_origins(
                origin_command_lib, Notice(warnings, 'warning'))
        if 'names' in pkg_dict and len(pkg_dict['names']) > 1:
            pkg_list = convert_to_pkg_dicts(pkg_dict)
            for pkg_dict in pkg_list:
                pkg = Package(pkg_dict['name'])
                pkg.fill(pkg_dict)
                image_layer.add_package(pkg)
    # if there is no listing add a notice
    else: