fswatch is a file change monitor that receives notifications when the contents
of the specified files or directories are modified.

fswatch implements four kinds of monitors:
  A monitor based on the File System Events API of Apple OS X.
  A monitor based on kqueue, supported on most *BSD systems, including OS X.
  A monitor based on inotify, a Linux kernel subsystem.
  A monitor which periodically stats the file system, which works anywhere
    stat (2) can be used.