A sample gulp file with minifies and watchers

gulpfile.js

var gulp = require("gulp");
var minifyHtml = require("gulp-minify-html");
var minifyCss = require("gulp-minify-css");
var uglify = require("gulp-uglify");
var concat = require("gulp-concat");

var paths = {
    scripts: "src/js/*.js",
    styles: "src/css/*.css",
    html: "src/*.html"
}

gulp.task("minify-html", function(){
     
     gulp.src(paths.html)
    .pipe(minifyHtml())
    .pipe(gulp.dest('.'));
});

gulp.task("merge-minify-js", function(){
      gulp.src(paths.scripts)
     .pipe(concat("main.min.js"))
     .pipe(uglify())
     .pipe(gulp.dest("build/js"));
      
});

gulp.task("merge-minify-css", function(){
      gulp.src(paths.styles)
     .pipe(concat("custom.min.css"))
     .pipe(minifyCss())
     .pipe(gulp.dest("build/css"));
});

// Rerun the task when a file changes
gulp.task('watch', function() {
  
  gulp.watch(paths.scripts, ['merge-minify-js']);
  gulp.watch(paths.styles, ['merge-minify-css']);
  gulp.watch(paths.html, ['minify-html']);

});


gulp.task("default", ["watch", "minify-html", "merge-minify-js", "merge-minify-css"]);