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.