Sample

gulpfile.js

'use strict';

// including plugins
var gulp = require('gulp'),
    concat = require("gulp-concat"),
    minifyCss = require("gulp-minify-css"),
    uglify = require("gulp-uglify"),
    watch = require('gulp-watch'),
    sass = require('gulp-sass'),
    autoprefixer = require('gulp-autoprefixer');

//  sourcemaps = require('gulp-sourcemaps')


// task JS
/*gulp.task('js', function () {
    gulp.src(getPaths('forAll', 'js')) // path to your files
        .pipe(concat('forAll.min.js'))
        .pipe(uglify())
        .pipe(gulp.dest(bu + 'build/js'));
});*/

gulp.task('watch', function () {
    gulp.watch('../**/*.scss', ['scss']);
});

// Путь от этого файла к публичной дирктории
var bootstrap = '../lib/bootstrap4/scss/bootstrap.scss'; // Base url
var customCss = '../css/custom.scss'; // Base url
var microrulesCss = '../css/microrules.scss'; //

gulp.task('scss', function () {
    return gulp.src([bootstrap, customCss, microrulesCss])
        .pipe(sass().on('error', sass.logError))
        .pipe(sass({outputStyle: 'compressed'}))
        // .pipe(minifyCss())
        .pipe(autoprefixer({
            browsers: ['last 2 versions'],
            cascade: false
        }))
        .pipe(gulp.dest('../css'));
});

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