Run a command when the filesystem changes

runwhen.py

#!/usr/bin/env python

import os
import sys
from time import sleep

usable_files = (
    # Customize this as you see fit
    '.py',
    '.php',
    '.yaml',
)

if len(sys.argv) != 3:
    print "Usage: {0} PATH 'SOME COMMAND TO RUN'".format(sys.argv[0])
    sys.exit(1)

path, execute = sys.argv[1:3]

def get_usable_filenames(path):
    for root, dirs, files in os.walk(path):
        for filename in files:
            if filename.endswith(usable_files):
                yield os.path.join(root, filename)

def get_file_hash(filename):
    info = os.stat(filename)
    return filename, info.st_size, info.st_mtime

def get_state(path):
    return set(map(get_file_hash, get_usable_filenames(path)));

old_state = get_state(path)
new_state = old_state

while True:
    if old_state != new_state:
        print
        old_state = new_state
        os.system(execute)
    else:
        sys.stdout.write(".")
        sys.stdout.flush()
        sleep(2)
    new_state = get_state(path)

tdaemon is too specific to Python and the very particular test harnesses tdaemon explicitly supports. Most other test-runner things (like python-gorun) use inotify, which is great, except that it doesn't work over HGFS (vmware file sharing) or on OSX. (incron falls into this category, too)

The overhead of doing a stat call on relevant filenames in a tree is pretty small. If it's small enough for you, then there's no reason to use something more complicated.

In my case, I run the script from my OSX host, and have it SSH into a vmware development image to run the test command itself.