#delta

This is a haskell library for monitoring filesystem changes. It is FRP based but also provides a callback API.

This library currently offers two methods for detecting file changes:

• Polling of directories in given time intervals
• Using the FSEvents - API (OS X only)

Usage

FRP interface (using Sodium)

Import the module System.Delta and then call the function deltaDir on the path you want to monitor. The value you get back is an instance of the class FileWatcher but it will later depend on your OS.

The generated value offers three Events:

• changedFiles
• newFiles
• deletedFiles

Callback interface

The function deltaDirWithCallbacks gives you an instance of the datatype CallbackWatcher that wraps a FileWatcher.

You can add an arbitrary number of callbacks to instances of that type with:

• withChangedCallback
• withNewCallback
• withDeletedCallback

These operations give you back a CallbackId which lets you delete callbacks from the CallbackWatcher using unregisterCallback.

Command line interface

delta-run

This package includes a handy little executable called delta-run which allows you to run a command on your terminal each time a file in the directory you are watching changes.

This is especially handy if you want to recompile some code each time it changes, but there are a lot of other useful applications.

Usage: delta-run [-i|--interval INTERVAL] FILE CMD

Available options:
  -h,--help                Show this help text
  -i,--interval INTERVAL   Run at most every n seconds
  FILE                     The directory that is watched
  CMD                      The command to run

delta-cli (demo only)

This cabal package also ships an executable called delta-cli that currently watches a directory that you give as an argument

delta-cli /path/to/my/directory

outputs:

new:     /path/to/my/directory/file
changed: /path/to/my/directory/file
new:     /path/to/my/directory/file2
del:     /path/to/my/directory/file

Hosting

This package is hosted on hackage