perl hash的问题，请大家帮助解决！在线等待！

[sunauqt]

%test = (
"one" => "100",
"two" => "200",
"three" => "50"
);
while(($index,$value) = each(%test)) {
$msg = "$index---$value\n";
open(FILE,">>test.log");
print FILE $msg;
close FILE;
}
我想把这个HASH按VALUE值从大到小排列后再写入到LOG文件中去，该如何做呢？

[tl66]

%test = (
"one" => "100",
"two" => "200",
"three" => "50"
);
open(FILE,">test.log");
foreach (sort {$test{$b} <=> $test{$a}} keys %test){
$msg = "$_---$test{$_}\n";
print FILE $msg;
}
close FILE;

[sunauqt]

能解释一下这是什么意思吗？
foreach (sort {$test{$b} <=> $test{$a}} keys %test){
$msg = "$_---$test{$_}\n";
print FILE $msg;
}