print header;
&load($cgi);

sub load()
{
 $cgi = shift;
 if (!$cgi->param('submit'))
  {
   $cgi=&showhtml($cgi);
   exit;
  }
  <....carry on with other task.....>
}

sub showhtml()
{
 my $cgi=shift;
 print $cgi->start_html();
 print $cgi->checkbox(-name="1",values=>"1",-onClick=>"this.form.submit()),checkbox(-name="2",values=>"2",-onClick=>"this.form.submit());
 my $a=$cgi->param("1");
 my $b=$cgi->param("2");
 if($a)
 {
  <show textbox;>
 }
 if($b)
 {
 <show textbox;>
 }

print $cgi->submit(-name=>'submit',-value=>'submit');
}