Glimpse (which stands for GLobal IMPlicit SEarch) is an indexing and
query system that allows you to search through all your files very
quickly. For example, finding 296 lines containing 'whitehouse' in 8750
files occupying 104MB took 6 seconds on a SUN Sparc 5.

Glimpse supports most of agrep's options (agrep is our powerful version
of grep) including approximate matching (e.g., finding mis- spelled
words), 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.