Darn:
```ruby
require 'io/wait'

f=File.open('CHANGELOG.md')
f.close

IO.select([f],[f],[f],0) # => error
f.ready? # => error
f.read_nonblock(6) # => error
```
found ready? on [stack overflow][]

[stack overflow]: http://stackoverflow.com/questions/930989/is-there-a-simple-method-for-checking-whether-a-ruby-io-instance-will-block-on-r