sub href_or_scalar {
    my $param = shift;
    my ($is_scalar, $is_hashref) = (0,0);
    if ( ! ref $param ) {
        $is_scalar = 1;
    }
    elsif ( ref $param eq 'HASH' ) {
        $is_hashref = 1;
    }
    else {
        die("I only accept a scalar or a HASHref!");
    }

    print STDERR "'$param' is: (scalar => $is_scalar, hashref => $is_hashref)\n";
}

href_or_scalar( 'hello!');
href_or_scalar( 'HASH' );
href_or_scalar( { key => 'value' } );
href_or_scalar( [ 'key' => 'value' ] );

__END__
'hello!' is: ( scalar => 1, hashref => 0)
'HASH' is: ( scalar => 1, hashref => 0)
'HASH(0x225490)' is: ( scalar => 0, hashref => 1)
I only accept a scalar or a HASHref! at c:\test.pl line 12.