tab@music4:~ $ perl -de 1

Loading DB routines from perl5db.pl version 1.51
Editor support available.

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

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

  DB<2> use Data::Dumper;

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

  DB<4> if ( exists $hash{nothing} ) { print "Wow.\n"; }

  DB<5> !3
print Dumper(\%hash)
$VAR1 = {};

  DB<6>