use strict;
use warnings;
use utf8;
use open ":utf8";
binmode STDIN, ':encoding(cp932)';
binmode STDOUT, ':encoding(cp932)';
binmode STDERR, ':encoding(cp932)';

open(DATAFILE, "< data.txt") or die("Error");

while(my $line = <DATAFILE>){
  chomp($line);
  print "$line\n";
}

close(DATAFILE);

open(DATAFILE, ">>", "data.txt") or die("Error");

print DATAFILE "追加\n";

close(DATAFILE);