sub write_list_to_logfile {
  my ( $list, $logfile ) = @_;
  open my $file, '>', $logfile or die "Can't open $logfile: $!";
  foreach my $line ( @$list ){
    print $file "$line\n";
  }
  close $file;
}

##</code><code>##

if ( keys(%known_dirs) ) {
  my @known_dirs = keys(%known_dirs);
  my $known_dirs_filename = "$dir/known_dirs.list";
  write_list_to_logfile(\@known_dirs, $known_dirs_filename);
}