rb-inotify

This is a simple wrapper over the inotify Linux kernel subsystem for monitoring changes to files and directories. It uses the FFI gem to avoid having to compile a C extension.

API documentation is available on rdoc.info.

Basic Usage

The API is similar to the inotify C API, but with a more Rubyish feel. First, create a notifier:

notifier = INotify::Notifier.new

Then, tell it to watch the paths you're interested in for the events you care about:

notifier.watch("path/to/foo.txt", :modify) {puts "foo.txt was modified!"}
notifier.watch("path/to/bar", :moved_to, :create) do |event|
  puts "#{event.name} is now in path/to/bar!"
end

Inotify can watch directories or individual files. It can pay attention to all sorts of events; for a full list, see the inotify man page.

Finally, you get at the events themselves:

notifier.run

This will loop infinitely, calling the appropriate callbacks when the files are changed. If you don't want infinite looping, you can also block until there are available events, process them all at once, and then continue on your merry way:

notifier.process

Advanced Usage

Sometimes it's necessary to have finer control over the underlying IO operations than is provided by the simple callback API. The trick to this is that the {INotify::Notifier#to_io Notifier#to_io} method returns a fully-functional IO object, with a file descriptor and everything. This means, for example, that it can be passed to IO#select:

 # Wait 10 seconds for an event then give up
 if IO.select([notifier.to_io], [], [], 10)
   notifier.process
 end

It can even be used with EventMachine:

 require 'eventmachine'
 EM.run do
   EM.watch notifier.to_io do
     notifier.process
   end
 end

Unfortunately, this currently doesn't work under JRuby. JRuby currently doesn't use native file descriptors for the IO object, so we can't use the notifier's file descriptor as a stand-in.