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.
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