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  1. cros/
  14. OWNERS

Chromite CLI Framework

This directory contains the core CLI system.

This document covers the common APIs chromite provides when writing tools. It does not get into CLI best practices as the CLI Guidelines document covers that more generally already.

Adding a new command

New commands can be added by creating a new file in cros/ that follows the cros_{command_name}.py format where the command can live.

The command class's implementation must:

  • Be a subclass of cli.command.Command
  • Have a @command.command_decorator('command-name') decorator on the class
  • Define an EPILOG class constant
  • Implement the @classmethod AddParser(cls, parser)
  • Implement Run(self)

Rules of thumb:

  • The Run method should not be a full implementation of the command.
    • It should validate the raw arguments.
    • It should translate arguments to chromite constructs as applicable.
    • It should then call a reusable implementation (e.g. in service/).
    • Otherwise, it may be a wrapper around a command outside of chromite.

Argument Parser

Chromite has a subclass of argparse.ArgumentParser in the lib.commandline module. The ArgumentParser subclass adds some common functionality, and a set of standard arguments that all scripts can take advantage of.

Custom Argument Types

There are a number of custom types defined for the ArgumentParser, which can be used with type='custom_type_name'.

  • ab_url: Parse android build urls.
  • bool: Parse standard shell boolean values (y/yes, n/no, 1, 0, true, false).
  • build_target: Does a regex validation of the name and produces a BuildTarget instance.
  • date: Parse the argument as a Y-m-d formatted date.
  • path: Expands ~/ paths and then standardizes to the real path.
  • path_exists: Expands ~/ paths and standardizes to the real path, then checks that the path exists.
  • file_exists: Expands ~/ paths and standardizes to the real path, then checks that the path exists and is a file.
  • dir_exists: Expands ~/ paths and standardizes to the real path, then checks that the path exists and is a directory.
  • gs_path: Processes all known GS urls and provides the equivalent gs:// url.
  • local_or_gs_path: Processes the argument as a ‘path’ or a ‘gs_path’, as needed.
  • path_or_uri: Like local_or_gs_path, but also parse other uri formats.

Argument Deprecation Functionality

The ArgumentParser also provides support for the deprecated argument in the ArgumentParser.add_argument method. This argument allows marking an argument as deprecated by printing a warning message, but still processes the argument as it normally would. Using the --foo argument below would produce something like the following log message.

parser.add_argument('--foo', type=int, deprecated='Use --bar instead!')
Argument --foo is deprecated: Use --bar instead!

Defined Arguments

logging=True (default) enables standard logging options:

  • --log-level=<level>: The minimum logging level (default: info).
  • --log-format=<format>: Change log line format.
  • -v, --verbose: Sets the verbose option to true and sets the log-level to info.
  • --debug: Sets verbose and debug options to true and sets the log-level to debug.
  • --color, --no-color: Control log coloring.

The caching= option (disabled by default) enables the common cache dir, and exposes the options:

  • --cache-dir=<dir>: Override the cache directory.

The dryrun= option (disabled by default) enables:

  • -n, --dry-run: Don't run commands, and show what would be done.

The filter= option (disabled by default) sets up a generic filter for tools that process user-specified paths. This filter can be accessed via .filter in the parsed options object; see chromite.utils.path_filter.PathFilter for more details. It also enables:

  • --include=<pattern>: Paths to include in the filter.
  • --exclude=<pattern>: Paths to exclude from the filter.

The jobs= option (disabled by default) enables:

  • -j, --jobs: Run multiple tasks in parallel using all available cpus.

Standard Arguments

Generally scripts are welcome to use any arguments they need. However, in the interest of standardizing the tools, some arguments have been defined as being reserved for specific usages. Not all the arguments will always apply, but when they are used, this is the form they must have.

-b--build-targetBuild Target

Build Target

This is the new version of the --board option that is in scripts pre-dating the standards. The build target option comes with parsing support in the form of the build_target type. The build target type will validate the name and construct a BuildTarget instance to assign to the variable rather than just storing the string.

parser.add_argument('-b', '--build-target', type='build_target')


The device argument is a long-standing type that just did not always use the same argument naming conventions. The device parser supports USB, File, SSH, and Servo. A specific device argument can accept any or all of the supported types. The example below supports USB and File, but not SSH or Servo.

    '-d', '--device',


The package(s) argument should be a positional argument taking one or more packages as appropriate. The requirements for what must be included in the specified package(s) are dependent on the script itself.

parser.add_argument('packages', nargs='+')