# Assume: version strings have same numbers of parts.  Adjust if not.
# Note: This is not efficient, but may help explain what needs to happen.
sort {
    my @a_fn_parts  = split( qr([_]), $a );
    my @a_ver_parts = split( qr([.]), @a_fn_parts[1] );

    my @b_fn_parts  = split( qr([_]), $b );
    my @b_ver_parts = split( qr([.]), @b_fn_parts[1] );

    my $i = 0;
    while ( $i < @a_ver_parts ) {
        return $a_ver_parts[ $i ] <=> $b_ver_parts[ $i ]
            if ( $a_ver_parts[ $i ] != $b_ver_parts[ $i ] );
        $i++;
    }
    return 0;
}