I ran the hsdb Command Line Debugger (Windows -> Console menu item) and tried the class and classes commands, and neither appeared to produce any output. Other commands seemed to work as expected. I then went back to the terminal window I used to launch hsdb, and notice all the output from class and classes commands went there instead. The reason is because these commands are using System.out.println instead of out.println. "out" is a PrintStream field of the CommandProcessor instance that is setup when constructed, and should be used for all output other than error output, which can use "err", although it seems most error output is actually using "out" instead.