watch command to run a script on filesystem changes

[sandreas]

I would like to have a watch command to watch a directory for filesystem changes and run shell commands, so that it is possible to watch a directory with audio books and start a conversion tool, as soon as new files are put in.

Important Note:
Maybe this exceeds the scope of tone as an audio tagger and has to be extracted in an extra tool (like fswatch, fswatcher, fsmon or baywatch - last name is to prevent name conflicts with existing more popular tools like https://github.com/emcrisostomo/fswatch)

Tasks:

• implement watch command with a --directory parameter to specify the directory
• add --debounce-milliseconds=<timespan> parameter to prevent running immediately on a change (e.g. when still copying files) to prevent too early execution
• add --event-type parameter (multiple usage) to watch for specific events (changed, renamed, created, deleted)

Optional tasks / ideas:

• implement --ignore-errors parameter for e.g. directory is not existing (retry to register the filesystem watcher
• implement --retry-on-error-milliseconds for --ignore-errors

Example:

tone watch --directory="/tmp/dir/" --debounce-milliseconds="300000" ls /tmp/dir