Reloading a Shiny application on source changes

I have been trying to implement watching for changes to source code and auto reloading a Shiny application. The problem being that Shiny applications only reload changes to server.R and ui.R by default, which isn’t so useful when your app gets complicated and you want to make it more modular.

Option 1 - Shell goodness :)

Initially I wanted to add minimal new stuff to my tool chain so I was looking for something that I could do in a shell script. My initial solution was inotify-tools. Simple to install:

sudo apt-get install inotify-tools

And once I got my head around some shell scripts malarkey, simple to configure by creating a watch.sh script:

#!/bin/sh

WATCHED_DIR=${1-./app}
PORT=${2-5000}

start () {
  R -e "shiny::runApp('$WATCHED_DIR', port = $PORT)" &
  PID=$!
}

start

inotifywait -mr $WATCHED_DIR --format '%e %f' \
  -e modify -e delete -e move -e create \
  | while read event file; do

  echo $event $file

  kill $PID
  start

done

By default this watches ./app directory and restarts the Shiny application on port 5000 whenever a file or directory change is detected (modified, deleted, moved or created). You can also override the path and port on the command line, eg:

./watch.sh ./src 5001

Awesome :) and I’m so pleased with it that I just had to record it here for posterity. The fact is though that I don’t use it anymore (I used it for about 5 minutes). The reason being that next I wanted to integrate LiveReload to also refresh my browser window on updates.

Option 2 - Ruby magic!

The simplest way for me to run a LiveReload server was with the guard-livereload ruby gem. This means installing guard and running that. So let’s face it, if I’m going to run guard anyway, there’s not much point reloading the application with inotifywait when I could also use guard-process. So I made sure I had ruby and bundler installed:

sudo apt-get install ruby
sudo apt-get install ruby-dev
sudo gem install bundler

Created the following Gemfile:

source "https://rubygems.org"

gem 'guard'
gem 'guard-livereload'
gem 'guard-process'

And installed dependencies:

bundle install

Created the following Guardfile:

dir = 'app'
port = 5000

guard 'process', name: 'Shiny', command: ['R', '-e', "shiny::runApp('#{dir}', port = #{port})"] do
  watch(%r{#{dir}/.+\.R$})
end

guard 'livereload', grace_period: 0.5 do
  watch(%r{#{dir}/.+\.R$})
end

Note the order of the guards to ensure the restart happens before browsers are notified and the configured grace_period for LiveReload to ensure that the application has finished starting.

Now running:

bundle exec guard

• Launches my application on port 5000
• Watches for changes then
  • reloads the application
  • reloads connected browsers running the LiveReload plugin