my $i=$t;
        $bill_table->Button(-text=>'Submit',
                        -command=>sub{if ($checkboxvalue[$i] ==1){print $f}},
                        )->pack;

##</code><code>##

        $bill_table->Button(-text=>'Submit',
                        -command=>[
                           sub{
                             my $valref = shift;
                             my $valname=shift;
                             if ($$valref ==1){print $valname}
                           },
                           \$checkboxvalue[$t],
                           $f,
                        ],
                        )->pack;

##</code><code>##

  if( $foo ){ print $f }
  if( defined $foo ){ print $f }

  if( $foo && $foo==1){ print $f }
  if( defined $foo && $foo==1){ print $f }