# Create some subroutines to find:
sub PACKAGEA::PACKAGEB::test {}
sub PACKAGED::test {}
sub test {}

# Create some packages without the subroutine:
$PACKAGEA::PACKAGEB::PACKAGEC::ANYVAR = 1;
$PACKAGEE::ANYVAR = 1;

sub find_sub {
   my ($sub_name) = @_;

   my @pkgs_with_sub;
   my $helper;

   # $helper must be initialized seperately from its definition.
   $helper = sub {
      my ($pkg_name) = @_;


      my $pkg = do { no strict 'refs'; \%{$pkg_name.'::'} };

      push(@pkgs_with_sub, $pkg_name)
         if   $pkg->{$sub_name}
         && *{$pkg->{$sub_name}}{CODE};


      my $pkg_name_ = ($pkg_name eq 'main'
         ? ''
         : $pkg_name.'::'
      );

      /^(.*)::$/ && $1 ne 'main' && &$helper($pkg_name_.$1)
         foreach (keys(%$pkg));
   };

   &$helper('main');

   return @pkgs_with_sub;
}

print(join(', ', check_for_sub('test')), $/);
# Prints "main, PACKAGEA::PACKAGEB, PACKAGED"