while( my @cols= splice @files, 0, 4 ) {
  my @table_cells;
                                                                                
  for( 0..3 ) {
    push @table_cells => $cols[$_]
      ? submit(-name=>'file', -value=> basename($cols[$_]))
      : ' ';
  }
                                                                                
  print Tr( {-align=>'center'}, td(\@table_cells) );
}