From ROSBag

A python-script called plot_bag_file.py, located at asl_gremlin_pkg/scripts/ was written to plot the recorded data using ROS-BAG. In-order to plot use the following syntax,
First go to the directory where plot_bag_file.py is located. Then

./plot_bag_file <bag-file>

where <bag-file> is the bag-file to plot(along with it's full-path).

For example, let's say that the bag-file is saved under /home/user1/bag_files as asl_gremlin_pkg_ 2017-12-09-00-36-01.bag. Then

./plot_bag_file.py /home/user1/bag_files/asl_gremlin_pkg_ 2017-12-09-00-36-01.bag

(or)

./plot_bag_file.py ~/bag_files/asl_gremlin_pkg_ 2017-12-09-00-36-01.bag