Gulp example

gulpfiles.js

var gulp       = require('gulp')
    , less     = require('gulp-less')
    , plumber  = require('gulp-plumber')
    , replace  = require('gulp-replace')
    , jshint   = require('gulp-jshint')
    , concat   = require('gulp-concat');

var cfg = {

    files: {

        less: [
            'frontend/less/vendor/fonts.less',
            'frontend/less/vendor/**',
            'frontend/less/theme/_*.less',
            'frontend/less/theme/layout.less',
            'frontend/less/theme/**'
        ],

        js: [
            'frontend/js/vendor/jquery.js',
            'frontend/js/vendor/**',
            'frontend/js/main/**'
        ],

        assets: 'frontend/assets/**'
    },

    dist: {

        css: {
            name: 'main.css',
            dir: './wp-content/themes/default/assets/css/'
        },

        js: {
            name: 'main.js',
            dir: './wp-content/themes/default/assets/js/'
        },

        assets: {
            dir: './wp-content/themes/default/assets/'
        }
    }
};

gulp.task('stylesheets', function() {
    gulp.src(cfg.files.less)
        .pipe(plumber())
        .pipe(concat(cfg.dist.css.name))
        .pipe(less())
        .pipe(replace(/(background: url)\(([^\)]+)\)/g, '$1(/wp-content/themes/default/assets/images/$2)'))
        .pipe(gulp.dest(cfg.dist.css.dir));
});

gulp.task('javascripts', function() {
    gulp.src(cfg.files.js)
        .pipe(plumber())
        .pipe(concat(cfg.dist.js.name))
        .pipe(gulp.dest(cfg.dist.js.dir));

    gulp.src(cfg.files.js.concat('!./frontend/js/vendor/**'))
        .pipe(plumber())
        .pipe(jshint())
        .pipe(jshint.reporter('default'));
});

gulp.task('watch', function(){
    gulp.watch(cfg.files.less,     ['stylesheets']);
    gulp.watch(cfg.files.js,       ['javascripts']);
});

gulp.task('build', ['stylesheets', 'javascripts']);
gulp.task('default', ['build', 'watch']);