A hash is like an array but the index can be text instead of a number. so when you write

my %hash = (  key1 => 'value1',
              key2 => 'value2',
              key3 => 'value3',
              key3 => 'value3',
              key3 => 'value3',
              key1 => 'value3',
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the second time you do key1 => ... it will overwrite any earlier value of key1.

There will only ever be one value associated with each key, so when you

foreach (sort keys %hash) {
   $hist{$_}++;
}
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each key will be unique, so the count will be one for each of them

You need to study hashes more. Perhaps perldsc will be of help