Good times with Watchr, Coffeescript and LESS

With this little gem you can watch specific folders or file extensions and run commands based on the files you watch.

By Stef van den Ham — May 16 2012

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!

Tags: less coffeescript


As always, if you have any questions or comments, you can find me on Twitter.

Be notified of new posts. Subscribe to the RSS Feed.