package MyModule;
use File::Rsync;
my %rsync_out;
my $rsync=File::Rsync->new( { outfun => \&rsync_out,
                              errfun => \&rsync_out,
                          } );
...
sub rsync_out {
  my ($message, $type)=@_;
  $rsync_out{$type}.="$message\n";
}