#!/usr/bin/perl -w
use strict;
use warnings;
use Data::Dumper;

my %test = (1=>'a',3=>'c');

print Dumper(\%test);
test_sub(\%test);
print Dumper(\%test);

sub test_sub {
    my ($test) = @_;
    %$test = (); # gut
    %{$test} = (); # besser? was ist richtiger?
}