there is currently no explicit command line tool which converts from ros1 to ros2. however, the current rosbag2 cli allows to replay ros1 bag files and can thus be used to record a new ros2 bag file based on the replay of ros1.
you can find a bit of documentation here on how to replay ros1 bag files: https://github.com/ros2/rosbag2_bag_v...
In order to use the plugins, again, the ROS 1 installation must be sourced before sourcing the ROS 2 installation. You can then just use the plugin through the regular interface.
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For playing, one can similarly write:
ros2 bag play -s rosbag_v2 <path_to_bagfile>
If there is ROS 1 data where no topic matching exists to ROS 2 these topics are ignored when replying. When calling ros2 bag info, one can see a list of mismatching topics:
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that being said, the api is functional enough to replay ros1 bag files and i believe it shouldn't be too hard to develop a real conversion tool for it based on that API.