The problem is that "Unicode format" is not a character encoding, and is a very non-precise term.

Chances are that the file is either encoded in UCS2 or in UTF-16LE. So to open the file, do something along these lines:

open my $handle, '<:encoding(UTF-16LE)', $filename
   or die "Can't open file '$filename' for reading: $!";
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For more information on unicode handling please read Perl and character encodings, perluniintro and the documentation for the Encode module.