use Data::Dumper;

my %people;
while (<DATA>)
{
  chomp;
  my ($name, $group, $manager) = split/,/; # Don't do that, use Text::CSV instead
  if ($group)
  {
    ${ $people{$name}{Group} } = $group; # Autovivification means: if the reference exists, change the value, else, create a new reference
  }
  else
  {
    $people{$name}{Group} = \${ $people{$manager}{Group} }; # Autovivification again
  }
}
print Dumper \%people;
print ${ $people{"Woody Boyd"}{Group} };
__DATA__
Sam Malone,Cheers,Rebecca Howe
Woody Boyd,,Rebecca Howe
Rebecca Howe,Cheers,Rebecca's Manager