In addition to the traditional command line search programs, locate and find, OS X provides a command line interface to the Spotlight search system (mdfind).
While I can't find it documented anywhere, my guess is that "mdfind" stands for "meta data find".
Simple spotlight search
Search in a specific directory
mdfind -onlyin /Users/keithw searchterm
Search for specific meta data
mdfind "kMDItemAuthor == '*Donaldson*'"
List available meta data fields
Turn off spotlight indexing for a volume
mdutil -i off volumename
Turn on spotlight indexing for a volume
mdutil -i on volumename
Show the status of spotlight indexing for a volume
mdutil -s volumename
How spotlight does its magic
Unlike the locate program and database, spotlight recognizes and indexes file system changes almost immediately. How is that possible? The magic happens in the kernel, which sends notices of file system changes to a special character device named
/dev/fsevents. Spotlight monitors this special device and learns about new files that need to be indexed. There is no published API for
/dev/fsevents, as far as I can tell.