How to search multiple separate WP installs on one domain in one search box

I have been thinking about this a lot as I have three separate blogs installed on one domain … one is in the main root, another in a subdomain and another in a sub-directory of main domain.

So I’d like one search box that would allow me to search all of them an return the results on one page. Yes, I know you could do a google search box for the domain … but what about if — like in my case — some of the posts are password protected and not indexed by Google but I still need them returned. Only way is to do a database search …

One solution I am thinking of — which is a pain in the butt but may work.

1. Create a new WP database —

2. export as XML all posts from all three blogs, so you have three XML files

3. import all three XML files into the new WP install and maybe add the proper directory / location for each separate blog into a custom field …

4. then you just search this new install which has everything, create a custom field output on a custom search page that link you to the proper link on the original blog … have a custom search page on the new install that handles properly directing you to the correct place.

Then just setup a chron to do the migration of the three separate databases to the main one at regular intervals and you should be good to go.

Let me know what you think, if you know of a better way or have any suggestions.