I am a Mac OS X program that watches for changes to a directory tree. Whenever I see a change, I run a program. For example, I can run make whenever you change your source code.

I am a Python script. I use the Mac OS X FSEvents library to detect filesystem changes.

auto path childProgram [childArg1 childArg2 ...]

First, I run childProgram, passing in the childArgN arguments given. Then I watch for any change to the directory tree rooted at path. Whenever I see a change, I run childProgram with its arguments again.

I wait 100 milliseconds after seeing a change before running the program. Additional changes in that period won't make me run the program extra times.

For example, I can run make whenever the current directory tree changes:

auto . make

Note that if make makes any changes to the current directory tree, I will immediately run it again. If make is fast and idempotent, this shouldn't cause any trouble. However, it's usually better to put your source code in a separate subdirectory from your build products.

For example, if you keep your source code in subdirectory src, I can run make install whenever the src tree changes:

auto src make install

I don't use the shell automatically, so if you need it, you have to ask for it:

auto src sh -c 'cd build && make -f ../Makefile install'