Programming Perl, by Wall, Christiansen and Orwant, O'Reilly.

Perl Debugger Pocket Reference, by Richard Foley, O'Reilly.

Perl Debugged, by Peter Scott and Ed Wright, Addison-Wesley.

Perl Medic, by Peter Scott, Addison-Wesley.

perldebug man page

perldiag man page

“brian d foy's guide to debugging”: www.panix.com/~comdog/solve_any_perl_problem.pod