#Watchman exists to #watch #files and #record when they change. It can also trigger actions (such as rebuilding assets) when matching files #change.

Concepts
Watchman can recursively watch one or more directory trees (we call them roots).
Watchman does not follow symlinks. It knows they exist, but they show up the same as any other file in its reporting.
Watchman waits for a root to settle down before it will start to trigger notifications or command execution.
Watchman is conservative, preferring to err on the side of caution; it considers files to be freshly changed when you start to watch them or when it is unsure.
You can query a root for file changes since you last checked, or the current state of the tree
You can subscribe to file changes that occur in a root

facebook.github.io/watchman/