bad command-line args\n$usage
EOF
if ($opt->{help}) { print $help; exit 0 };
-my $old_dir = shift(@ARGV) or die $usage;
-my $new_dir = shift(@ARGV) or die $usage;
+my $old_dir = shift(@ARGV) // '';
+my $new_dir = shift(@ARGV) // '';
+die $usage if (scalar(@ARGV) || $new_dir eq '' || $old_dir eq '');
die "$new_dir exists\n" if -d $new_dir;
die "$old_dir not a directory\n" unless -d $old_dir;