use Getopt::Std;
my %opt;
getopt('abc',\%opt);
Multivalued(\%opt);

#...

sub Multivalued { # convert lists to array refs.
    my $href = shift;
    while( my ($k, $v ) = each %$href ) {
        my @anon = split /\,/, $v or next;
        $href -> { $k } = \@anon;
    }
}