How do I make rostopic hz print a single line only?

edit

Sorry, wrong command in the question. I updated it to rostopic hz...

Thx. I'll check it out...

... as I am running rostopic hz in a docker container with docker-py: How I can interface with (ros/ros_comm/tools/rostopic/src/rostopic/__init__.py, lines 103 to 270) with plain Ubuntu terminal (which is "exposed" via docker-py)?

You wouldn't. You probably need to write a small script that outputs what you want using the class I linked to.

Or: contribute a -n COUNT option to rostopic hz itself. That would be +100.

I am going for "Or: contribute a -n COUNT option to rostopic hz itself." over the longer term for sure. For now I just stick to my very dirty workaround (running every subsequent command in separate containers).

I believe that the reason that hz doesn't have a COUNT right now is that it's debatable whether it would make sense: rostopic hz needs some time to properly calculate the msg rate, so simply looking at the first output may not be entirely representative.

If you're doing this for some testing purpose, you might want to take a look at ipa-fmw/atf, particularly publish_rate.

"rostopic hz needs some time to properly calculate the msg rate, so simply looking at the first output may not be entirely representative." I agree. I don't know much about the implementation of rostopic hz but using it is probably just a rough estimate anyway? A rough estimate is fine for me here.