A grunt file for web development. Demonstrates watching multiple files, but only running a task on changed files (FYI makefiles are really good at that).

gruntfile.js

module.exports = function (grunt) {
    'use strict';

    // Project configuration.
    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),
        sass: {
            build: {
                files: [{
                    expand: true,
                    cwd: 'src',
                    src: ['**/*.scss'],
                    dest: 'build',
                    ext: '.css',
                    filter: function (filepath) {
                        var ignore = {
                            'variables.scss': true
                        };
                        return !ignore[filepath.split('/').pop()];
                    }
                }]
            },
            all: {}
        },
        haml: {
            build: {
                files: [{
                    expand: true,
                    cwd: 'src',
                    src: ['**/*.haml'],
                    dest: 'build',
                    ext: '.html',
                    filter: function (filepath) {
                        // Bit of a hack to get this task to ouput exactly which files are compiled.
                        grunt.log.writeln('File ' + filepath.cyan + ' compiling.');
                        return true;
                    }
                }]
            },
            all: {}
        },
        coffee: {
            build: {
                expand: true,
                cwd: 'src',
                src: ['**/*.coffee'],
                dest: 'build',
                ext: '.js'
            },
            all: {}
        },
        watch: {
            sass: {
                files: ['src/**/*.scss'],
                tasks: ['sass:all'],
                options: {
                    spawn: false
                }
            },
            haml: {
                files: ['src/**/*.haml'],
                tasks: ['haml:all'],
                options: {
                    spawn: false
                }
            },
            coffee: {
                files: ['src/**/*.coffee'],
                tasks: ['coffee:all'],
                options: {
                    spawn: false
                }
            }
        }
    });

    grunt.event.on('watch', function (action, filepath) {
        if (grunt.file.isMatch(grunt.config('watch.sass.files'), filepath)) {
            grunt.config('sass.all.src', filepath);
            grunt.config('sass.all.dest', filepath.replace('src/', 'build/').replace('.scss', '.css'));
        } else if (grunt.file.isMatch(grunt.config('watch.haml.files'), filepath)) {
            grunt.config('haml.all.src', filepath);
            grunt.config('haml.all.dest', filepath.replace('src/', 'build/').replace('.haml', '.html'));
        } else if (grunt.file.isMatch(grunt.config('watch.coffee.files'), filepath)) {
            grunt.config('coffee.all.src', filepath);
            grunt.config('coffee.all.dest', filepath.replace('src/', 'build/').replace('.coffee', '.js'));
        }
    });

    // Load the required plugins.
    grunt.loadNpmTasks('grunt-contrib-sass');
    grunt.loadNpmTasks('grunt-contrib-haml');
    grunt.loadNpmTasks('grunt-contrib-coffee');
    grunt.loadNpmTasks('grunt-contrib-watch');

    // Tasks.
    grunt.registerTask('default', ['sass', 'haml', 'coffee']);
};