gulpfile.js

// Assigning modules to local variables
var gulp = require('gulp'),
  sass = require('gulp-sass'),
  sasslint = require('gulp-sass-lint'),
  cssmin = require('gulp-cssmin'),
  autoprefixer = require('gulp-autoprefixer'),
  header = require('gulp-header'),
  rename = require('gulp-rename'),
  pkg = require('./package.json');

// Set the banner content
var banner = [
  '/*!\n',
  ' * Bootstrap4 Solarized - Official Website (<%= pkg.homepage %>)\n',
  ' * Copyright 2016-' + new Date().getFullYear(),
  ' <%= pkg.author.name %>\n',
  ' * Licensed under <%= pkg.license %>\n',
  ' */\n',
  ''
].join('');

// sass task to compile the sass files and add the banner
gulp.task('sass', function() {
  return gulp
    .src('./sass/*.scss')
    .pipe(sass().on('error', sass.logError))
    .pipe(header(banner, { pkg: pkg }))
    .pipe(gulp.dest('dist/css'));
});

// Fonts
gulp.task('fonts', function() {
  return gulp.src(['./fonts/**']).pipe(gulp.dest('dist/fonts/'));
});

// Minify CSS
gulp.task('minify', gulp.series(gulp.parallel('sass')), function() {
  return gulp
    .src(['./dist/css/*.css', '!./dist/css/*.min.css'])
    .pipe(rename({ suffix: '.min' }))
    .pipe(autoprefixer())
    .pipe(cssmin())
    .pipe(gulp.dest('dist/css'));
});

// Lint SASS
gulp.task('lint', function() {
  return gulp
    .src('sass/**/*.s+(a|c)ss')
    .pipe(sasslint())
    .pipe(sasslint.format())
    .pipe(sasslint.failOnError());
});

// Watch task monitors SASS files
gulp.task('watch', function() {
  gulp.watch('sass/*.scss', ['sass']);
  gulp.watch('dist/css/*.css', ['minify']);
});

// Default task
gulp.task('default', gulp.series(gulp.parallel('fonts', 'sass', 'minify')));