use PerlIO::encoding;

# Modify a copy of a file...
sub foo {
  my $thing_to_do_ref = shift;
  my @lines;
  if (open IN, "<", "$some_path") {
    binmode IN, ":encoding(UTF-16LE)";
    while ( my $a_line = <IN> ) {
    
      # Do stuff to $a_line...
      
      }
      push @lines, $a_line;
    }
    close IN;
    
    if (open OUT, ">", "$some_other_path") {
      binmode OUT, ":encoding(UTF-16LE)";
      while (@lines) {
        my $line = shift @lines;
        print OUT "$line\n";
      }
      close OUT;
    } else {
      print "Oops! Could not write: $! \n";
    }
  } else {
    print "Oops! Could not read: $! \n";
  }
}