[9fans] nb—search and index notes in files by keyword

[Jason Catena <jason.catena@gmail.com>]

http://swtools.wordpress.com/2010/03/05/nb%E2%80%94search-and-index-notes-in-files-by-keyword/

This isn't complicated, but it hit a sweet spot with me, since I like
to break up information into smallish chunks and index it by keyword.
It collects the keywords into one file per directory, and keeps a list
of all the indexes in a file in $HOME.  It searches all the existing
indexes for the given keyword, then reconstructs the index for the
current directory, so it presents slightly older results fast.  Its
relationship with plan9 is that it's written in rc, and outputs lines
in a /path/file:line format for right-clicking with acme.  I'm posting
it here because I find it really useful, and I wish I'd come up with
it years ago.  The more you put into it the more useful it becomes,
since it's got a fine degree of granularity (the particular keywords
attached to a bit of information) and composability of keywords (just
string a few grep and grep -v after the nb command).

Jason Catena