[boyter]

I have written about it all here (I maintain searchcode.com ) http://www.boyter.org/category/searchcode/ specifically http://www.boyter.org/2013/02/why-code-search-is-difficult/ is of note.

If you want to see implementations I suggest looking at https://github.com/OpenGrok/OpenGrok https://github.com/ggreer/the_silver_searcher https://github.com/google/codesearch and my own https://github.com/boyter/searchcode-server