@liste=($eins,$zwei,$drei);

$eins->{DATE}="2005-01-01";
$zwei->{DATE}="2004-12-20";
$drei->{DATE}="2005-01-02";

 @sortListe=($zwei,$eins,$drei);

use strict;
sub create_obj {
  my $self = {};
  bless $self;
  return $self;
}

my $obj1 = create_obj();
my $obj2 = create_obj();
my $obj3 = create_obj();

$obj1->{DATE}="2005-01-01";
$obj2->{DATE}="2004-12-20";
$obj3->{DATE}="2005-01-02";

sub sort_rule {
  my ($year1,$month1,$day1) = split /-/,$a->{DATE};
  my ($year2,$month2,$day2) = split /-/,$b->{DATE};
  return $year1 <=> $year2 or
         $month1 <=> $month2 or
         $day1 <=> $day2
        ;
}

my @list = ($obj1,$obj2,$obj3);

print $_->{DATE},"\n" for sort sort_rule @list;

use strict;
package Test;

sub new {
  my $self = {};
  bless $self;
  return $self;
}

package main;

my $obj1 = Test->new();
my $obj2 = Test->new();
my $obj3 = Test->new();

$obj1->{DATE}="2005-01-01";
$obj2->{DATE}="2004-12-20";
$obj3->{DATE}="2005-01-02";


my @list = ($obj1,$obj2,$obj3);

print $_->{DATE},"\n" for sort {$a->{DATE} <=> $a->{DATE}} @list;
_ _ END _ _ 
2005-01-01
2004-12-20
2005-01-02

my @sort_liste = sort { $a->{DATE} <=> $b->{DATE} } @liste;

$a->{DATE} <=> $a->{DATE}

$a->{DATE} <=> $a->{DATE}

$eins->{DATE}="2005-01-01";
$zwei->{DATE}="2005-01-02";
$drei->{DATE}="2004-12-20";
$eins->{ID}=1;
$zwei->{ID}=2;
$drei->{ID}=5;
@liste=($eins,$zwei,$drei);
my @sort_liste = sort { $b->{DATE} <=> $a->{DATE} } @liste;
for ( @sort_liste ) { print "datum: ",$_->{DATE}, "\n";
                           print " id: ",$_->{DATE},"\n";}

datum: 2005-01-01
id: 1
datum: 2005-01-02
id: 2
datum: 2004-12-20
id: 5



 das gleiche aber mit "cmp" ergibt


datum: 2005-01-02
id: 2
datum: 2005-01-01
id: 1
datum: 2004-12-20
id: 5

Binary "<=>" returns -1, 0, or 1 depending on whether the left argument
is numerically less than, equal to, or greater than the right argument.
If your platform supports NaNs (not-a-numbers) as numeric values, using
them with "<=>" returns undef. NaN is not "<", "==", ">", "<=" or ">="
anything (even NaN), so those 5 return false. NaN != NaN returns true,
as does NaN != anything else. If your platform doesn't support NaNs then
NaN is just a string with numeric value 0.

    perl -le '$a = NaN; print "No NaN support here" if $a == $a'
    perl -le '$a = NaN; print "NaN support here" if $a != $a'