How to save point cloud file from rosbag?

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I am trying to save point cloud data to a pcd file using pcl_ros

rosrun pcl_ros bag_to_pcd scan data.bag ./pcd

But all I see in /pcd output directory is just one pcd file. Looks like data is being overwritten to 0.000000000.pcd for each point cloud frame over the time and I only have one file at the end as output.

How can I ensure all the data can be saved in separate individual pcd file?