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.

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

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.

If you get an error like inotify event queue has overflowed you might be running into system limits. You can add the following to your /etc/sysctl.conf to increase the number of files that can be monitored:

fs.inotify.max_user_watches = 100000
fs.inotify.max_queued_events = 100000
fs.inotify.max_user_instances = 100000

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Released under the MIT license.

Copyright, 2009, by Natalie Weizenbaum. Copyright, 2017, by Samuel G. D. Williams.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.