I'm not certain about command line tools, but I like using ObjectAid for reverse engineering into class diagrams:
http://www.objectaid.com/
You can easily add any class with it's relationships to an ObjectAid graph. It saves the file in an XML format with the ucls extension. Here's a sample:
You can also use PlantUML, but it's better for forward engineering than reverse engineering:
http://plantuml.sourceforge.net/
PlantUML has its own unique syntax that you can get source for, too - but it's not nearly as easy to pull together as ObjectAid
Both of these work as eclipse plug-ins, sorry that I don't know more about any command line tools that might be able to do what you're asking.