Good times with Watchr, Coffeescript and LESS

Posted May 15th, 2021 • 3 min read

I have been working on a pure HTML front-end for one of the pet projects I'm doing. A lot of fun, but while developing, running the terminal commands to compile both the .less and .coffee files gets a tad tedious. "Watchr" to the rescue! With this little gem you can watch specific folders or file extensions and run commands based on the files you watch.

Here is how I got it set up now ..

Installing watchr

First of all we need to get the Watchr gem installed. Assuming you have a Mac and got XCode (or at least the tools) installed, this is pretty simple:

$ gem install watchr

Installing coffeescript

Another easy one ..

$ npm install -g coffee-script

Don't forget the -g flag as you (probably) want it to be installed globally.

Installing the LESS compiler

You got the hang of it now, it's as easy as ..

$ npm install -g less

The fun part!

Now we're ready for the fun bit, setting up watchr to do some automagic stuff.

I have a typical folder structure, with the exception of a new _src folder which will contain all the raw coffeescript and less files.


Watchr works with a config file, which basically tells it what to watch for, and what to do if it finds any changes. I placed the file inside the _src folder and named it watchr.rb

Here's my config file at the moment:

def compile_less
    %x[lessc less/bootstrap/bootstrap.less ../css/main.css --yui-compress]

def compile_coffee
    %x[coffee -c -j ../js/app.js coffee/]

def do_growl(message)
  growlnotify = `which growlnotify`.chomp
  title = "Watchr Message"
  passed = message.include?('0 failures, 0 errors')
  image = passed ? "~/.watchr_images/passed.png" : "~/.watchr_images/failed.png"
  severity = passed ? "-1" : "1"
  options = "-w -n Watchr --image '#{File.expand_path(image)}'"
  options << " -m '#{message}' '#{title}' -p #{severity}"
  system %(#{growlnotify} #{options} &)

do_growl "Watching folders and waiting for changes .."

watch('less/*') { |m|
    # Recompile LESS files
    do_growl "LESS Compiled and Compressed!"

watch('coffee/*') { |m|
    # Recompile Coffeescripts
    do_growl "Coffeescripts compiled and concatenated!"

As you can see at the bottom I'm watching the 2 folders seperately, as I want to run different commands for them. For the project I'm working on I'm using Twitter Bootstrap, so rather than compiling all the .less files to seperate .css files I just want to compiled bootstrap.less as that @imports all the things it needs. When it's done with that it yui-compresses the lot and writes the output to css/main.css. Pretty cool!

The compile_coffee command does something pretty similar. Whenever a .coffee file in the coffee folder changes it will compile them all and combine the output (notice the -j flag) and write it to js/app.js.

To get the show on the road, cd to the _src folder, and run:

$ watchr watchr.rb

You may have noticed the do_growl function, which doesn't really add value except that it's just cool to get a Growl message whenever it has done it's thing. To get that bit working you have to install "Growl Notify".

If you're not that interested, or you don't have a Mac with Growl simply remove the function and the do_growl calls from the watch patterns.

I'm sure I could optimize this a bit, and add variables for output folders and options, but for now it's simple, working, and pretty damn cool.

Let me know how you get your watchr set up!

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