Watch the File System for Changes

R binding for libfswatch, a file system monitoring library. This uses an optimal event-driven API for each platform:

• ReadDirectoryChangesW on Windows
• FSEvents on MacOS
• inotify on Linux
• kqueue on BSD
• File Events Notification on Solaris/Illumos

Watching is performed asynchronously in the background, without blocking the session.

• Watch files, or directories recursively.
• Log activity, or call an R function, upon every change event.

Install watcher from CRAN with:

install.packages("watcher")

watcher requires the ‘libfswatch’ library.

• On Linux / MacOS, an installed version will be used if found in the standard filesystem locations.
• On Windows, or if not found, the bundled version of ‘libfswatch’ 1.19.0-dev will be compiled from source.
• Source compilation of the library requires ‘cmake’.

Create a ‘Watcher’ using watcher::watcher().

By default this will watch the current working directory recursively and write events to stdout.

Set the callback argument to run an R function, or rlang-style formula, every time a file changes:

• Uses the ‘later’ package to execute the callback when R is idle at the top level, or whenever later::run_now() is called, for instance automatically in Shiny’s event loop.
• Function is called back with a character vector of the paths of all files which have changed.

library(watcher) dir <- file.path(tempdir(), "watcher-example") dir.create(dir) w <- watcher(dir, callback = ~print(.x), latency = 0.5) w #> <Watcher> #> Public: #> get_path: function ()  #> initialize: function (path, callback, latency)  #> is_running: function ()  #> start: function ()  #> stop: function ()  #> Private: #> path: /tmp/RtmpslHgGB/watcher-example #> running: FALSE #> watch: externalptr w$start() file.create(file.path(dir, "newfile")) #> [1] TRUE file.create(file.path(dir, "anotherfile")) #> [1] TRUE later::run_now(1) #> [1] "/tmp/RtmpslHgGB/watcher-example/newfile" #> [1] "/tmp/RtmpslHgGB/watcher-example/anotherfile" newfile <- file(file.path(dir, "newfile"), open = "r+") cat("hello", file = newfile) close(newfile) later::run_now(1) #> [1] "/tmp/RtmpslHgGB/watcher-example/newfile" file.remove(file.path(dir, "newfile")) #> [1] TRUE later::run_now(1) #> [1] "/tmp/RtmpslHgGB/watcher-example/newfile" w$stop() unlink(dir, recursive = TRUE, force = TRUE)

Thanks to the authors of libfswatch, upon which this package is based:

• Alan Dipert
• Enrico M. Crisostomo