doc/dev/plugins/problems/gulpfile.js

var gulp = require('gulp');
var sass = require('gulp-sass');
var cleancss = require('gulp-clean-css');
var csscomb = require('gulp-csscomb');
var rename = require('gulp-rename');
var autoprefixer = require('gulp-autoprefixer');
var sourcemaps = require('gulp-sourcemaps');

// configure the paths
var watch_dir = './scss/*.scss';
var src_dir = './scss/*.scss';
var dest_dir = './css';

var paths = {
    source: src_dir
};

gulp.task('watch', function() {
    gulp.watch(watch_dir, ['build']);
});

gulp.task('build', function() {
    gulp.src(paths.source)
        .pipe(sourcemaps.init())
        .pipe(sass({outputStyle: 'compact', precision: 10})
            .on('error', sass.logError)
        )
        .pipe(sourcemaps.write())
        .pipe(autoprefixer())
        .pipe(gulp.dest(dest_dir))
        .pipe(csscomb())
        .pipe(cleancss())
        .pipe(rename({
            suffix: '.min'
        }))
        .pipe(gulp.dest(dest_dir));
});

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