use CGI;
@array1 = param('datalist1');
@array2 = param('datalist2');
@array3 = param('datalist3');

##</code><code>##

my %data = map { $_ => [param $_] } qw(datalist1 datalist2 datalist3);

##</code><code>##

sub compare {
  my @lengths = map { scalar @{$data{$_}} } qw(datalist1 datalist2 datalist3);
  my $first = shift @lengths;
  $first == $_ or return 0 for @lengths;
  return 1;
}