> perl -de 1

Loading DB routines from perl5db.pl version 1.27
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(-e:1):   1
  DB<1> %hoh = ();

  DB<2> use Data::Dumper;

  DB<3> print Dumper(\%hoh)
$VAR1 = {};

  DB<4> if (exists($hoh{nothing}{second})) { print "wow.\n"; }

  DB<5> !3
print Dumper(\%hoh)
$VAR1 = {
          'nothing' => {}
        };