I have benefitted from what's here, and applied it to my situation (i.e. perldb in emacs) by: (perldb "perl -I<path-to-override.pm> -Moverride <other-args>) Perl's -M command line arg makes sure you override module is 'use'd in any perl pgm that you run via perldb this way, without having to add 'use' statements to existing code.