<?php
/**
 * Workflow event "Log publishing": writes one line per published version to var/log/mysite_hello.log.
 * Use it on the trigger content / publish / after.
 */
class mysitePublishLogType extends eZWorkflowEventType
{
    const WORKFLOW_TYPE_STRING = 'mysitepublishlog';

    public function __construct()
    {
        parent::__construct( self::WORKFLOW_TYPE_STRING,
                             ezpI18n::tr( 'extension/mysite_hello', 'Log publishing' ) );
        $this->setTriggerTypes( array( 'content' => array( 'publish' => array( 'after' ) ) ) );
    }

    public function execute( $process, $event )
    {
        $parameters = $process->attribute( 'parameter_list' );
        $objectID = isset( $parameters['object_id'] ) ? (int)$parameters['object_id'] : 0;
        $version = isset( $parameters['version'] ) ? (int)$parameters['version'] : 0;

        $object = eZContentObject::fetch( $objectID );
        if ( !$object instanceof eZContentObject )
        {
            // nothing to log; let the operation continue
            return eZWorkflowType::STATUS_ACCEPTED;
        }

        eZLog::write( sprintf( 'Published object %d version %d: %s', $objectID, $version, $object->attribute( 'name' ) ),
                      'mysite_hello.log' );

        return eZWorkflowType::STATUS_ACCEPTED;
    }
}

eZWorkflowEventType::registerEventType( mysitePublishLogType::WORKFLOW_TYPE_STRING, 'mysitePublishLogType' );

<?php /* #?ini charset="utf-8"?

[EventSettings]
ExtensionDirectories[]=mysite_hello
AvailableEventTypes[]=event_mysitepublishlog

*/ ?>

<div class="element">
    <p>{'Log publishing'|i18n( 'extension/mysite_hello' )}</p>
</div>

php -l extension/mysite_hello/eventtypes/event/mysitepublishlog/mysitepublishlogtype.php
php bin/php/ezcache.php --clear-all