Sounds very much like homework, so I'll just give you a tip: a hash (e.g. %data) would come in handy. You can use the data (A(01), B(02), etc) as keys and the number of times you encounter the data as values. 

  $data{$line}++;

[download]
would do the trick.

As a final step, you iterate over the keys (the function keys is useful here) in the hash and print those keys that have values larger than 1.

Hope this helps, -gjb-

In reply to Re: finding duplicate data by gjb
in thread finding duplicate data by harry34

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