{watchr} provides functions for watching files and then running code whenever those files change.

You can install the development version of {watchr} from GitHub with:

# install.packages("devtools")
devtools::install_github("tomjemmett/watchr")

There are two functions, watch_files_and_run_function and watch_files_and_start_task.

Both functions take the same arguments, but the difference is the former runs the function in the same R process, so the check for files changing is blocked until the function completes. The latter starts running a task in the background, the task is killed and restarted each time the files change.

The task function is designed for long running tasks, e.g. running a shiny application.

The files which you want to monitor are passed into the ... argument. This allows you to pass in lists of files, or functions that return lists of files.

For example, you could monitor the files in the R/ directory, and the DESCRIPTION file like so:

watch_files_and_run_function(
  \() print("files changed"),
  "DESCRIPTION",
  dir("R/", pattern = "*.R")
)

However, if we were to add files to the R/ directory, these wont be detected until we restart the watch function. Instead, you could pass in an anonymous function to run the dir function every time the watch function runs, like so:

watch_files_and_run_function(
  \() print("files changed"),
  "DESCRIPTION",
  \() dir("R/", pattern = "*.R")
)