node.js - Only compile sass if a file has changed using gulp -

i'm trying rebuild gulp file bit more efficient, , i'm having trouble getting styles task compile if file has changed.

i found this question, answer doesn't seem working me.

let's have repo organized so:

/dev   /assets     /styles       all.css /src   /assets     /styles       all.scss       _header.scss gulpfile.js package.json 

i want overwrite all.css if change has been made in either of sass files. so, if save _header.scss no changes had been made, , ran styles task, should realize code hasn't changed , not overwrite all.css.

i looking @ gulp-cached, per question linked above, doesn't seem working me. here's task @ it's basic:

var gulp = require("gulp"),     cached = require("gulp-cached"),     sass = require("gulp-sass");  gulp.task("styles", function() {     return gulp.src(src + "/assets/styles/all.scss")         .pipe(sass().on("error", sass.logerror))         .pipe(cached("sass_compile")) // should skip dest if cache same         .pipe(gulp.dest(dev + "/assets/styles")); }); 

the cached pipe doesn't seem working in instance. run gulp styles , still overwrites all.css, if no changes have been made, if didn't re-save file.

the more complex task i'd use is:

var gulp = require("gulp"),     cached = require("gulp-cached"),     sourcemaps = require("gulp-sourcemaps"),     sass = require("gulp-sass"),     autoprefixer = require("gulp-autoprefixer"),      // set environment paths     src = "./src",     dev = "./dev",     dist = "./dist";  gulp.task("styles", function() {     return gulp.src(src + "/assets/styles/all.scss")         .pipe(sourcemaps.init())         .pipe(sass().on("error", sass.logerror))         .pipe(autoprefixer("last 2 version", "ie 8", "ie 9"))         .pipe(sourcemaps.write())         .pipe(cached("sass_compile")) // should skip dest if cache same         .pipe(gulp.dest(dev + "/assets/styles")); }); 

would appreciate guidance on this. much.

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edit 1: note all.scss in demo contains @import "_header";.

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edit 2: okay, figured out gulp-cached seems working fine in watch task. revised question: how can same type of functionality outside of watch task?

try gulp-changed instead. believe works on last modified date of file, sounds want.