sub print_diff {
    my ( $decor, $dir, @filename ) = @_;
    my $prefix = (
        ( $opt_plain ? "$decor " : '' )
        . ( defined $dir ? "$dir " : '' )
    );
    print map "$prefix$_\n", @filename;
}

if ( not( $opt_bonly or $opt_jonly ) ) {
    print_diff '<', $dirname1, diff( \@dir1, \@dir2 );
}
if ( not( $opt_aonly or $opt_jonly ) ) {
    print_diff '>', $dirname2, diff( \@dir2, \@dir1 );
}
if ( $opt_inter or $opt_jonly ) {
    print_diff '=', '', isect( \@dir1, \@dir2 );
}