grunt-contrib-watch

Run predefined tasks whenever watched file patterns are added, changed or deleted.

Note that this plugin has not yet been released, and only works with the latest bleeding-edge, in-development version of grunt. See the When will I be able to use in-development feature 'X'? FAQ entry for more information.

Getting Started

If you haven't used grunt before, be sure to check out the Getting Started guide.

From the same directory as your project's Gruntfile and package.json, install this plugin with the following command:

npm install grunt-contrib-watch --save-dev

Once that's done, add this line to your project's Gruntfile:

grunt.loadNpmTasks('grunt-contrib-watch');

If the plugin has been installed correctly, running grunt --help at the command line should list the newly-installed plugin's task or tasks. In addition, the plugin should be listed in package.json as a devDependency, which ensures that it will be installed whenever the npm install command is run.

The watch-examples task

Examples

// Simple config to run jshint any time a file is added, changed or deleted
grunt.initConfig({
  watch: {
    files: '**/*',
    tasks: ['jshint']
  }
});

// Advanced config. Run specific tasks when specific files are added, changed or deleted.
grunt.initConfig({
  watch: {
    gruntfile: {
      files: 'Gruntfile.js',
      tasks: ['jshint:gruntfile'],
      options: {
        nocase: true
      }
    },
    src: {
      files: ['lib/*.js', 'css/**/*.scss', '!lib/dontwatch.js'],
      tasks: ['default']
    },
    test: {
      files: '<%= jshint.test.src %>',
      tasks: ['jshint:test', 'qunit']
    }
  }
});

The watch-faqs task

FAQs

How do I fix the error EMFILE: Too many opened files.?

This is because of your system's max opened file limit. For OSX the default is very low (256). Increase your limit with ulimit -n 10480, the number being the new max limit. If you're still running into issues then consider setting the option forceWatchMethod: 'old' to use the older and slower stat polling watch method.

The watch-options task

Settings

There are a number of options available. Please review the minimatch options here. As well as some additional options as follows:

files

Type: String|Array

This defines what file patterns this task will watch. Can be a string or an array of files and/or minimatch patterns.

tasks

Type: String|Array

This defines which tasks to run when a watched file event occurs.

options.interrupt

Type: boolean Default: false

As files are modified this watch task will spawn tasks in child processes. The default behavior will only spawn a new child process per target when the previous process has finished. Set the interrupt option to true to terminate the previous process and spawn a new one upon later changes.

Example:

watch: {
  scripts: {
    files: '**/*.js',
    tasks: ['jshint'],
    options: {
      interrupt: true
    }
  }
}

options.debounceDelay

Type: Integer Default: 500

How long to wait before emitting events in succession for the same filepath and status. For example if your Gruntfile.js file was changed, a changed event will only fire again after the given milliseconds.

Example:

watch: {
  scripts: {
    files: '**/*.js',
    tasks: ['jshint'],
    options: {
      debounceDelay: 250
    }
  }
}

options.interval

Type: Integer Default: 100

The interval is passed to fs.watchFile. Since interval is only used by fs.watchFile and this watcher also uses fs.watch; it is recommended to ignore this option. Default is 100ms.

options.forceWatchMethod

Type: false|'new'|'old' Default: false

Node.js has two file watching methods: 'old' (fs.watchFile) which uses stat polling and 'new' (fs.watch) which attempts to use the system's built-in watch mechanism. By default, this watch task uses both methods and which ever method responds first will be used for subsequent events.

There may be some setups where you would need to force a specific watch method, such as on networked file system. Set options.forceWatchMethod: 'old' to specifically use the old watch method, fs.watchFile.

The watch-overview task

Overview

Inside your Gruntfile.js file, add a section named watch. This section specifies the files to watch, tasks to run when an event occurs and the options used.

Release History

• 2012-10-31 - v0.1.4 - Prevent watch from spawning duplicate watch tasks
• 2012-10-27 - v0.1.3 - Better method to spawn the grunt bin Bump gaze to v0.2.0. Better handles some events and new option forceWatchMethod Only support Node.js >= v0.8
• 2012-10-16 - v0.1.2 - Only spawn a process per task one at a time Add interrupt option to cancel previous spawned process Grunt v0.3 compatibility changes
• 2012-10-15 - v0.1.1 - Fallback to global grunt bin if local doesnt exist. Fatal if bin cannot be found Update to gaze 0.1.6
• 2012-10-07 - v0.1.0 - Release watch task Remove spawn from helper Run on Grunt v0.4