rostopic pub - {stamp:now} vs --rate

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I would like publish a continuous flow messages on a topic from the terminal. In order to do that I use the --rate argument of the rostopic tool. However my message type contains a header field that I would like to fill automatically.

The ros documentation says that you can fill the header stamp automatically (ref) in this way:

$ rostopic pub my_topic my_msgs/StampedMsg '{header: auto}'

However, it looks that the timestamp field does not update when it is used with the --rate parameter. Instead it remains constant with the stamp of the first message of the flow.

$ rostopic pub my_topic my_msgs/StampedMsg '{header: auto}' --rate 5

Is there any way to use rostopic so that the stamp field is automatically filled and dynamically updated?