grunt-contrib-watch

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

Getting Started

This plugin requires Grunt ~0.4.0

If you haven't used Grunt before, be sure to check out the Getting Started guide, as it explains how to create a Gruntfile as well as install and use Grunt plugins. Once you're familiar with that process, you may install this plugin with this command:

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

Once the plugin has been installed, it may be enabled inside your Gruntfile with this line of JavaScript:

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

Watch task

Run this task with the grunt watch command.

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.nospawn

Type: Boolean Default: false

This instructs the watch task to not spawn task runs in a child process. Setting this option also speeds up the reaction time of the watch (usually 500ms faster for most) and allows subsequent task runs to share the same context (i.e., using a reload task). Not spawning task runs can make the watch more prone to failing so please use as needed.

Example:

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

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.event

Type: String|Array Default: 'all'

Specify the type watch event that trigger the specified task. This option can be one or many of: 'all', 'changed', 'added' and 'deleted'.

Example:

watch: {
  scripts: {
    files: '**/*.js',
    tasks: ['generateFileManifest'],
    options: {
      event: ['added', 'deleted']
    }
  }
}

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']
    }
  }
});

Using the watch event

This task will emit a watch event when watched files are modified. This is useful if you would like a simple notification when files are edited or if you're using this task in tandem with another task, for example a live reload task. Here is a simple example using the watch event:

grunt.initConfig({
  watch: {
    scripts: {
      files: ['lib/*.js'],
      tasks: [''],
    },
  },
});
grunt.event.on('watch', function(action, filepath) {
  grunt.log.writeln(filepath + ' has ' + action);
});

The watch event is not intended for replacing the standard Grunt API for configuring and running tasks. If you're trying to run tasks from within the watch event you're more than likely doing it wrong. Please read configuring tasks.

Compiling Files As Needed

A very common request is to only compile files as needed. Here is an example that will only lint changed files with the jshint task:

grunt.initConfig({
  watch: {
    scripts: {
      files: ['lib/*.js'],
      tasks: ['jshint'],
    },
  },
  jshint: {
    all: ['lib/*.js'],
  },
});

// on watch events configure jshint:all to only run on changed file
grunt.event.on('watch', function(action, filepath) {
  grunt.config(['jshint', 'all'], filepath);
});

If you save multiple files simultaneously you may opt for a more robust method:

var changedFiles = Object.create(null);
var onChange = grunt.util._.debounce(function() {
  grunt.config(['jshint', 'all'], Object.keys(changedFiles));
  changedFiles = Object.create(null);
}, 200);
grunt.event.on('watch', function(action, filepath) {
  changedFiles[filepath] = action;
  onChange();
});

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). Temporarily increase your limit with ulimit -n 10480, the number being the new max limit.

Can I use this with Grunt v0.3?

Yes. Although grunt-contrib-watch is a replacement watch task for Grunt v0.4, version grunt-contrib-watch@0.1.x is compatible with Grunt v0.3. grunt-contrib-watch >= 0.2.x is *only compatible and recommended to use with Grunt v0.4.

Why is the watch devouring all my memory?

Likely because of an enthusiastic pattern trying to watch thousands of files. Such as '**/*.js' but forgetting to exclude the node_modules folder with '!node_modules/**/*.js'. Try grouping your files within a subfolder or be more explicit with your file matching pattern.

Why spawn as child processes as a default?

The goal of this watch task is as files are changed, run tasks as if they were triggered by the user themself. Each time a user runs grunt a process is spawned and tasks are ran in succession. In an effort to keep the experience consistent and continualy produce expected results, this watch task spawns tasks as child processes by default.

Sandboxing task runs also allows this watch task to run more stable over long periods of time. As well as more efficiently with more complex tasks and file structures.

Spawning does cause a performance hit (usually 500ms for most environments). It also cripples tasks that rely on the watch task to share the context with each subsequent run (i.e., reload tasks). If you would like a faster watch task or need to share the context please set the nospawn option to true. Just be aware that with this option enabled, the watch task is more prone to failure.

Release History

• 2013-02-27   v0.3.1   Fix for top level options.
• 2013-02-26   v0.3.0   nospawn option added to run tasks without spawning as child processes. Watch emits 'watch' events upon files being triggered with grunt.event. Completion time in seconds and date/time shown after tasks ran. Negate file patterns fixed. Tasks debounced individually to handle simultaneous triggering for multiple targets. Errors handled better and viewable with --stack cli option. Code complexity reduced making the watch task code easier to read.
• 2013-02-14   v0.2.0   First official release for Grunt 0.4.0.
• 2013-01-17   v0.2.0rc7   Updating grunt/gruntplugin dependencies to rc6. Changing in-development grunt/gruntplugin dependency versions from tilde version ranges to specific versions.
• 2013-01-08   v0.2.0rc5   Updating to work with grunt v0.4.0rc5.
• 2012-12-14   v0.2.0a   Conversion to grunt v0.4 conventions. Remove node v0.6 and grunt v0.3 support. Allow watch task to be renamed. Use grunt.util.spawn "grunt" option. Updated to gaze@0.3.0, forceWatchMethod option removed.
• 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

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Task submitted by Kyle Robinson Young

This file was generated on Mon Apr 29 2013 14:56:52.