in reply to Remove find tag
The best way to handle xml files is with a module. If you look on CPAN you find some like XML::Simple or XML::Twig
Also you should change your data type to store your keys. Use a hash instead of an array. Why? Because a hash already makes sure that there no key can be repeated. And searching for a key is a lot faster than with an array.
If you don't know how to use a hash, read the docs. It is nearly as simple as an array, but sooo much better for most problems
UPDATE: This is not a code writing service. The script you had was not bad as a first draft. Adapt it a bit, debug it and it should work. Here is a hint:
#Suppose you got a new XML key and value read from the file in $key an +d $value if (not exists $hash{$key}) { $hash{$key}= $value; } else { #drop key }
This is already the meat of your hash handling.
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