Glimpse

Glimpse (which stands for GLobal IMPlicit SEarch) is a popular UNIX indexing and query system that allows you to search through a large set of files very quickly. Glimpse supports most of agrep's options (agrep is our powerful version of grep) including approximate matching, Boolean queries, and even some limited forms of regular expressions. It is used in the same way, except that you don't have to specify file names. So, if you are looking for a needle anywhere in your file system, all you have to do is say glimpse needle and all lines containing needle will appear preceded by the file name.