use Data::Dumper; use strict; use warnings; $|++; printf "D::D version %s\n",Data::Dumper->VERSION; for my $sk (0,1) { print "\$Data::Dumper::Sortkeys=$sk\n"; $Data::Dumper::Sortkeys=$sk; for my $up (1,0) { print "\$Data::Dumper::Useperl=$up\n"; $Data::Dumper::Useperl=$up; my %rev; my %name; print "Dumper:\n",Dumper(\%rev,\%name),"\n"; } } print "Done\n"; __END__ D::D version 2.121 $Data::Dumper::Sortkeys=0 $Data::Dumper::Useperl=1 Dumper: $VAR1 = {}; $VAR2 = {}; $Data::Dumper::Useperl=0 Dumper: $VAR1 = {}; $VAR2 = {}; $Data::Dumper::Sortkeys=1 $Data::Dumper::Useperl=1 Dumper: $VAR1 = {}; $VAR2 = {}; $Data::Dumper::Useperl=0 Use of uninitialized value in print at c:\temp\test_dd.pl line 15. Dumper: $VAR2 = {};