If you really want to learn some awesome debugging tricks, check out this lazy testing presentation. The author explains a bit about how the debugger works internally and then shows how you run tests inside of the debugger and have a new test script written when you're done. It's very impressive.

You can also script a debugging session. From perldebug:

You can mock TTY input to debugger by adding arbitrary commands to @DB::typeahead. For example, your .perldb file might contain

  sub afterinit { push @DB::typeahead, "b 4", "b 6"; }

Which would attempt to set breakpoints on lines 4 and 6 immediately after debugger initilization. Note that @DB::typeahead is not a supported interface and is subject to change in future releases.