Verschachtelte Hash mit Array

#!/usr/bin/perl

BEGIN {
%nav = ();
}

while (<DATA>) {
  chomp($_);
  my ($cat, $post) = split(/\:/, $_);
  $nav{$cat} = push(@{$nav{$cat}}, $post);
}

END {

foreach my $category(sort keys %nav) {
  print $category,"\n";  
  foreach my $article (sort {lc($a) cmp lc($b)} @{$nav{$category}} ) {
    print "- ",$article,"\n";  
  }
}

}
__DATA__
cat1:post1
cat1:post2
cat1:post3
cat2:post1
cat2:post2
cat3:post1
cat3:post2
cat3:post3