http://www.perlmonks.org?node_id=48516


in reply to How to debug unknown dynamic code?

If you're not able to check out the code to add print statements, how will you fix any bugs that you find?

Otherwise I was going to suggest that, at the points in the module where you want the debugger to break, you add the line: $DB::single = 1
(That's like hitting 's' in the debugger right at that line.)

This might help with setting breakpoints in the module: you can change which file you're looking at/setting breakpoints in/etc. by using the debugger's 'f' command.