Custom Rules action example

The actions being used inside rules and actions in trigger is not the same
But we can still take code example from rules/modules/*.rules.inc
and you will see lots of "core - optional" module rules

Rules action example module:

<?php
/**
 * hook_rules_action_info
 * @return
 *   An array of information about the module's provided rules actions.
 *   The array contains a sub-array for each action, with the action name as
 *   the key. Actions names may only contain lowercase alpha-numeric characters
 *   and underscores and should be prefixed with the providing module name.
 *   Possible attributes for each sub-array are:
 *   - label: The label of the action. Start capitalized. Required.
 *   - group: A group for this element, used for grouping the actions in the
 *     interface. Should start with a capital letter and be translated.
 *     Required.
 *   - parameter: (optional) An array describing all parameter of the action
 *     with the parameter's name as key. Each parameter has to be
 *     described by a sub-array with possible attributes as described
 *     afterwards, whereas the name of a parameter needs to be a lowercase,
 *     valid PHP variable name.
 *   - provides: (optional) An array describing the variables the action
 *     provides to the evaluation state with the variable name as key. Each
 *     variable has to be described by a sub-array with possible attributes as
 *     described afterwards, whereas the name of a parameter needs to be a
 *     lowercase, valid PHP variable name.
 *   - 'named parameter': (optional) If set to TRUE, the arguments will be
 *     passed as a single array with the parameter names as keys. This emulates
 *     named parameters in PHP and is in particular useful if the number of
 *     parameters can vary. Defaults to FALSE.
 *   - base: (optional) The base for action implementation callbacks to use
 *     instead of the action's name. Defaults to the action name.
 *   - callbacks: (optional) An array which allows to set specific function
 *     callbacks for the action. The default for each callback is the actions
 *     base appended by '_' and the callback name.
 *   - 'access callback': (optional) A callback which has to return whether the
 *     currently logged in user is allowed to configure this action. See
 *     rules_node_integration_access() for an example callback.
 *  Each 'parameter' array may contain the following properties:
 *   - label: The label of the parameter. Start capitalized. Required.
 *   - type: The rules data type of the parameter, which is to be passed to the
 *     action. All types declared in hook_rules_data_info() may be specified, as
 *     well as an array of possible types. Also lists and lists of a given type
 *     can be specified by using the notating list<integer> as introduced by
 *     the entity metadata module, see hook_entity_property_info(). The special
 *     keyword '*' can be used when all types should be allowed. Required.
 *   - bundles: (optional) An array of bundle names. When the specified type is
 *     set to a single entity type, this may be used to restrict the allowed
 *     bundles.
 *   - description: (optional) If necessary, a further description of the
 *     parameter.
 *   - options list: (optional) A callback that returns an array of possible
 *     values for this parameter. The callback has to return an array as used
 *     by hook_options_list(). For an example implementation see
 *     rules_data_action_type_options().
 *   - save: (optional) If this is set to TRUE, the parameter will be saved by
 *     rules when the rules evaluation ends. This is only supported for savable
 *     data types. If the action returns FALSE, saving is skipped.
 *   - optional: (optional) May be set to TRUE, when the parameter isn't
 *     required.
 *   - 'default value': (optional) The value to pass to the action, in case the
 *     parameter is optional and there is no specified value.
 *   - 'allow null': (optional) Usually Rules will not pass any NULL values as
 *     argument, but abort the evaluation if a NULL value is present. If set to
 *     TRUE, Rules will not abort and pass the NULL value through. Defaults to
 *     FALSE.
 *   - restriction: (optional) Restrict how the argument for this parameter may
 *     be provided. Supported values are 'selector' and 'input'.
 *   - default mode: (optional) Customize the default mode for providing the
 *     argument value for a parameter. Supported values are 'selector' and
 *     'input'. The default depends on the required data type.
 *   - sanitize: (optional) Allows parameters of type 'text' to demand an
 *     already sanitized argument. If enabled, any user specified value won't be
 *     sanitized itself, but replacements applied by input evaluators are as
 *     well as values retrieved from selected data sources.
 *   - translatable: (optional) If set to TRUE, the provided argument value
 *     of the parameter is translatable via i18n String translation. This is
 *     applicable for textual parameters only, i.e. parameters of type 'text',
 *     'token', 'list<text>' and 'list<token>'. Defaults to FALSE.
 *   - ui class: (optional) Allows overriding the UI class, which is used to
 *     generate the configuration UI of a parameter. Defaults to the UI class of
 *     the specified data type.
 *   - cleaning callback: (optional) A callback that input evaluators may use
 *     to clean inserted replacements; e.g. this is used by the token evaluator.
 *   - wrapped: (optional) Set this to TRUE in case the data should be passed
 *     wrapped. This only applies to wrapped data types, e.g. entities.
 *  Each 'provides' array may contain the following properties:
 *   - label: The label of the variable. Start capitalized. Required.
 *   - type: The rules data type of the variable. All types declared in
 *     hook_rules_data_info() may be specified. Types may be parametrized e.g.
 *     the types node<page> or list<integer> are valid.
 *   - save: (optional) If this is set to TRUE, the provided variable is saved
 *     by rules when the rules evaluation ends. Only possible for savable data
 *     types. Defaults to FALSE.
 */
function rules_example_rules_action_info(){
  return array(
   
'rules_example_extra_node_title' => array(
     
'group' => t('Example'),
     
'label' => t('Add prefix to node title'),
     
'parameter' => array(
       
//pass in parameters
       
'node' => array(
         
'type' => 'node',
         
'label' => t('Node'),
         
'description' => t('The node to add the prefix.'),
         
'save' => TRUE,
        ),
      ),
    ),
  );
}

/**
 * Rules action implementation
 * Key defined in hook_rules_action_info
 * @param  Object $node node being editted
 */
function rules_example_extra_node_title($node) {
 
$node->title .= '[Rules action example prefix] ';
 
node_save($node);
}
?>

It takes time to understand all hook_rules_action_info() parameters
perhaps take some code from rules modules and edit will be easier.

Google