use FileHandle;

my @list;
my $file;
my @d = ("ds","DD","df");

foreach $type (@d){
   $file = "list_".$type.".txt";
   open (fh, "<$file");
   @list = <fh>;
   close fh;
}
foreach $output (@list){
chomp $output;
print $output."\n";
}