use strict;
my %hash = ("woche1" => "4",
            "woche2" => "3",
            "woche3" => "1",
            "woche4" => "7",
            "woche5" => "2");
my @keys_sorted = sort{ $hash{$b} <=> $hash{$a} }keys %hash;
for my $key ( @keys_sorted ) {
    print "$key -> $hash{$key}\n";
}