Add support for content filters

[peci1]

Description

Now that content filters are supported in rclpy (ros2/rclpy#1506, ros2/rclpy#1521), it would make a lot of sense to allow passing a content filter to ros2 topic echo|bw|hz.

Motivation

This could serve as a debugging tool for writing the content filters, and also as a practical tool printing/measuring only messages of interest.

Design / Implementation Considerations

No response

Additional Information

No response

[Barry-Xu-2018]

These commands can be further optimized based on content filters 👍

[fujitatomoya]

@peci1 @Barry-Xu-2018

I am totally agree with ros2 topic echo with content filtering to print the only messages with specific contents.

on the other hand, how we can enhance hw | bw with content filtering? i mean how the statistics with specific contents can be beneficial for user or what kind of use cases do we have?

[peci1]

I agree that echo has the greatest value.

Regarding bw/hz, I mostly imagine that you write a filtered subscription in your code and you want to get an idea about how much data it actually is.

Think about the example of "throttle" filter. If you have a 10 Hz topic and you want to subsample it to 1 Hz, you write a filter like "header.stamp.nsec <= 1e8". And you want to verify you actually get a ~1 Hz topic.

[ros-discourse]

This issue has been mentioned on Open Robotics Discourse. There might be relevant details there:

https://discourse.openrobotics.org/t/ros-news-for-the-week-of-december-8th-2025/51376/1