perl -MData::Dumper -le 'my %hash;
while(<>) {
my ($field1,$field4)=(split /\s*;\s*/)[0,3];
push @{$hash{$field4}},$field1 }
 print Dumper(\%hash) ' test
$VAR1 = {
          '1' => [
                   '4'
                 ],
          '4' => [
                   '1',
                   '2'
                 ],
          '3' => [
                   '3'
                 ]
        };