You should really explain in plain English and in detail what you are trying to do, because your code does not make much sense in several places. Just an example in the beginning section:

# ...
  my %database;
  my @employee_details;
  my @mykeys;
  open(FH,"+>>database.txt")|| die 'Cannot open the file';
  print FH %database;
  close FH;
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You declare the %database hash, then open a file in read/append mode and print the hash to the file handler. But %database has just been defined and has not been populated at this point, so that you are printing empty content to the file (besides the fact that printing directly a hash to a file might not be the best).

Similarly, the elsif block ("get") does not make more sense.

Also I would strongly advise you to indent your code properly. This is very important for understanding the logic of a program.