python-openstackclient/doc/source/commands.rst

========
Commands
========


Command Structure
=================

OpenStackClient has a consistent and predictable format for all of its commands.

Commands take the form::

    openstack [<global-options>] <object-1> <action> [<object-2>] [<command-arguments>]

* All long options names begin with two dashes ('--') and use a single dash
  ('-') internally between words (--like-this).  Underscores ('_') are not used
  in option names.


Global Options
--------------

Global options are global in the sense that they apply to every command
invocation regardless of action to be performed. They include authentication
credentials and API version selection. Most global options have a corresponding
environment variable that may also be used to set the value. If both are
present, the command-line option takes priority. The environment variable
names are derived from the option name by dropping the leading dashes ('--'),
converting each embedded dash ('-') to an underscore ('_'), and converting
to upper case.

For example, ``--os-username`` can be set from the environment via ``OS_USERNAME``.


Command Object(s) and Action
----------------------------

Commands consist of an object described by one or more words followed by
an action.  Commands that require two objects have the primary object ahead
of the action and the secondary object after the action. Any positional
arguments identifying the objects shall appear in the same order as the
objects.  In badly formed English it is expressed as "(Take) object1
(and perform) action (using) object2 (to it)."

::

    <object-1> <action> <object-2>

Examples::

    group add user <group> <user>

    volume type list   # 'volume type' is a two-word single object


Command Arguments and Options
-----------------------------

Each command may have its own set of options distinct from the global options.
They follow the same style as the global options and always appear between
the command and any positional arguments the command requires.


Actions
-------

The actions used by OpenStackClient are defined below to provide a consistent meaning to each action. Many of them have logical opposite actions. Those actions with an opposite action are noted in parens if applicable.

* authorize - authorize a token (used in OAuth)
* add (remove) - add some object to a container object; the command is built in the order of "container add object" (<container> <object>), the positional arguments appear in the same order
* attach (detach) - deprecated; use add/remove
* create (delete) - create a new occurrance of the specified object
* delete (create) - delete a specific occurrance of the specified object
* detach (attach) - deprecated; use add/remove
* list - display summary information about multiple objects
* lock (unlock)
* migrate - move a server to a different host; --live performs a live migration if possible
* pause (unpause) - stop a server and leave it in memory
* reboot - forcibly reboot a server
* rebuild - rebuild a server using (most of) the same arguments as in the original create
* remove (add) - remove an object from a group of objects
* rescue (unrescue) - reboot a server in a special rescue mode allowing access to the original disks
* resize - change a server's flavor
* resume (suspend) - return a suspended server to running state
* save - download an object locally
* set (unset) - set a property on the object, formerly called metadata
* show - display detailed information about the specific object
* suspend (resume) - stop a server and save to disk freeing memory
* unlock (lock)
* unpause (pause) - return a paused server to running state
* unrescue (rescue) - return a server to normal boot mode
* unset (set) - remove an attribute of the object

Implementation
==============

The command structure is designed to support seamless addition of plugin
command modules via ``setuptools`` entry points.  The plugin commands must
be subclasses of Cliff's command.Command object.


Command Entry Points
--------------------

Commands are added to the client using ``setuptools`` entry points in ``setup.cfg``.
There is a single common group ``openstack.cli`` for commands that are not versioned,
and a group for each combination of OpenStack API and version that is
supported.  For example, to support Identity API v3 there is a group called
``openstack.identity.v3`` that contains the individual commands.  The command
entry points have the form::

    verb_object = fully.qualified.module.vXX.object:VerbObject

For example, the 'list user' command fir the Identity API is identified in
``setup.cfg`` with::

    openstack.identity.v3 =
        # ...
        list_user = openstackclient.identity.v3.user:ListUser
        # ...