Hobbes
Hobbes is a small UNIX-style file watcher for OSX windows, linux and OSX (thanks @cgag), written after experiencing some OSX bugs with my usual standby guard. The filenames of modified files are simply echoed to stdout, one file per line. You take it from there.
Complex tasks can be accomplished by combining hobbes with other commands such as xargs, for example:
# automatic GHC recompile when your source files change hobbes "*.hs" | xargs -n1 ghc --make
xargs -n1 <command> means essentially "run the command on each word of input". So ghc --make is run on each modified file.
Another example: I have a script called kick that reloads the current tab in Chrome and then refocuses iTerm. With this command to hobbes I get automatic browser reloading on every save. Script here if you're interested.
hobbes "*.html" | xargs -n1 kick
# running multiple commands when files change hobbes "*.elm" | xargs -n1 sh -c 'cmd1; cmd2; ...'
Installation with Stack
Hobbes can be installed from sources with stack:
$ git clone https://github.com/jhickner/hobbes.git
$ cd hobbes
$ stack installThanks
Hobbes is a very small wrapper around fsnotify.