Metricbeat - Add a custom field with existing value

Elastic Stack Beats
1

How can i add a custom field whose value will be equal to an exiting field
Eg

processors:
-add_fields:
    fields:
      new_field: host.name
2

Sorry for the late response. I believe you can use the add_fields processor in Metricbeat: https://www.elastic.co/guide/en/beats/metricbeat/current/add-fields.html

3

Yes, I know that new fields can be added. But my question is if that new field's value can be set from existing field-value.
For example make the new field value equal to the host.name.
Since host.name has the value equal to hostname of that system and which is already set by the metricbeat.