There is a command group 'az_eventgrid_system topic_event subscription'. This group of commands could 'manage event subscriptions of system topic'. The group of commands has global parameter '--debug' which means 'Increase logging verbosity to show all debug logs.'. The group of commands has global parameter '--help -h' which means 'Show this help message and exit.'. The group of commands has global parameter '--only-show-errors' which means 'Only show errors, suppressing warnings.'. The group of commands has global parameter '--output -o' which means 'Output format.'. The group of commands has global parameter '--query' which means 'JMESPath query string. See <a href="http://jmespath.org/">http://jmespath.org/</a> for more information and examples.'. The group of commands has global parameter '--subscription' which means 'Name or ID of subscription. You can configure the default subscription using `az account set -s NAME_OR_ID`.'. The group of commands has global parameter '--verbose' which means 'Increase logging verbosity. Use --debug for full debug logs.'. This group contains a child command 'az_eventgrid_system topic_event subscription_update'.The syntax is: az eventgrid system-topic event-subscription update --name
                                                    --resource-group
                                                    --system-topic-name
                                                    [--advanced-filter]
                                                    [--deadletter-endpoint]
                                                    [--endpoint]
                                                    [--endpoint-type {azurefunction, eventhub, hybridconnection, servicebusqueue, servicebustopic, storagequeue, webhook}]
                                                    [--included-event-types]
                                                    [--labels]
                                                    [--subject-begins-with]
                                                    [--subject-ends-with]. The 1th example of the child command would be to use it to 'update an event subscription for an event grid system topic to specify a new endpoint', the syntax is: az eventgrid system-topic event-subscription update --name es1 \
    -g rg1 --system-topic-name systemtopic1 --endpoint https://contoso.azurewebsites.net/api/f1?code=code. The 2th example of the child command would be to use it to 'update an event subscription for an event grid system topic to specify a new subject ends with filter', the syntax is: az eventgrid system-topic event-subscription update --name es2 \
    -g rg1 --system-topic-name systemtopic1 \
    --subject-ends-with .jpg. The 3th example of the child command would be to use it to 'update an event subscription for an event grid system topic to specify a new endpoint and a new subject ends with filter a new list of included event types', the syntax is: az eventgrid system-topic event-subscription update --name es3 \
    -g rg1 --system-topic-name systemtopic1 \
    --subject-ends-with .png \
    --endpoint https://contoso.azurewebsites.net/api/f1?code=code
    --included-event-types Microsoft.Storage.BlobCreated Microsoft.Storage.BlobDeleted. The 4th example of the child command would be to use it to 'update an event subscription for an azure event grid system topic  to include a deadletter destination', the syntax is: az eventgrid system-topic event-subscription update --name es2 \
    -g rg1 --system-topic-name systemtopic1 \
    --deadletter-endpoint /subscriptions/{SubID}/resourceGroups/TestRG/providers/Microsoft.Storage/storageAccounts/sa1/blobServices/default/containers/blobcontainer1. The 5th example of the child command would be to use it to 'update an event subscription for an azure event grid system topic  using advanced filters', the syntax is: az eventgrid system-topic event-subscription update --name es3 \
    -g rg1 --system-topic-name systemtopic1 \
    --endpoint https://contoso.azurewebsites.net/api/f1?code=code
    --advanced-filter data.blobType StringIn BlockBlob
    --advanced-filter data.url StringBeginsWith https://myaccount.blob.core.windows.net. The parameter '--name -n' is required. It is used to name of the event subscription.. The parameter '--resource-group -g' is required. It is used to name of resource group. you can configure the default group using `az configure --defaults group=<name>`.. The parameter '--system-topic-name' is required. It is used to name of the system topic.. The parameter '--advanced-filter' is optional. an advanced filter enables filtering of events based on a specific event property.. The parameter '--deadletter-endpoint' is optional. the azure resource id of an azure storage blob container destination where eventgrid should deadletter undeliverable events for this event subscription.. The parameter '--endpoint' is optional. endpoint where eventgrid should deliver events matching this event subscription. for webhook endpoint type, this should be the corresponding webhook url. for other endpoint types, this should be the azure resource identifier of the endpoint.. The parameter '--endpoint-type' is optional. the type of the destination endpoint.. The parameter '--included-event-types' is optional. a space-separated list of event types. example: microsoft.storage.blobcreated microsoft.storage.blobdeleted. to subscribe to all default event types, do not specify any value for this argument.. The parameter '--labels' is optional. a space-separated list of labels to associate with this event subscription.. The parameter '--subject-begins-with' is optional. an optional string to filter events for an event subscription based on a prefix. wildcard characters are not supported.. The parameter '--subject-ends-with' is optional. an optional string to filter events for an event subscription based on a suffix. wildcard characters are not supported.. 