use CGI;

my $query = CGI->new();

# get the data structure
my $ref_data= create_data_structure();

if ($query->param( "button" ) eq 'first') { 
                      display_first(  $query, $ref_data ) }
else                                      { 
                      display_second( $query, $ref_data ) }

sub display_first {
  my ( $query, $s1_data ) = @_;

  # declare your variables here
   
  ...
  # use $s1_data to do something in this sub

}

sub display_second {
  my ( $query, $s2_data ) = @_;

  # declare your variables here
   
  ...
  # use $s2_data to do something in this sub

}

sub create_data {
   ...
    create a hash data structure
   ...
   ...
   return \%hash;

}