!/perl
use strict;
use warnings FATAL => qw(all);

use Text::CSV_XS;
use Data::Dump;

my $csv_par = 
{ 
 binary => 1, auto_diag => 1, allow_whitespace => 1,	
 sep_char => ';', eol => $/, quote_char => undef, 
};

my $csv = Text::CSV_XS->new($csv_par);
my @data = @{ $csv->getline_all(*DATA) };
shift @data; # simply throw away the header.

my %main;
my %hash_old;

############### The first pass:
for my $row ( @data )
{
   $hash_old{$row->[0]} = $row->[1];
   $main{$row->[0]} = $row->[1];
}

my %hash_new;
############### All the remaining steps:
do
{
  
  for my $row (@data)
  {
     if ( $hash_old{$row->[1]} )
	 {
	    $hash_new{$row->[0]} = $row->[1];
		$main{ $row->[0] } = 
                  $main{ $row->[1] } || $row->[1];
	 }
  }
  %hash_old = ();
  $hash_old{$_} = $hash_new{$_} for keys %hash_new;
  %hash_new = ();
}
while ( scalar keys %hash_old );

############### Filling in the main number 
############### for the main number themselves:
for my $row ( @data )
{
  $main{$row->[1]} = $row->[1] 
    unless exists $main{$row->[1]} or $row->[1] eq "";
  $main{$row->[0]} = $row->[0]
    unless length($main{$row->[0]});  
}

# Sample chains:

# 123-234-345-456-567-678-789
# 117-228-339
# 131
# 213-324-435
# 372

dd \%main;