use File::Find::Rule;
my $rule =  File::Find::Rule->new;
  $rule->file;
  $rule->name( '*.txt' );
  my @files = $rule->in("/" );
  open(W,"> index.txt")|| die "can't open index.txt file";
foreach $files_name (@files)
{
    print W $files_name ;
    print W "\n";
}