javascript - gulp-header only inject if it is not there already? -

does know how accomplish injecting header if not there?

i using gulp-header plugin:

  injectcopyright() {     return gulp.src([       `${config.distdir}/**/*.js`,       `${config.distdir}/**/*.css`,       '!' + `${config.distvendorjsdir}/**`     ])       .pipe(header('/*\n' + copyright + '\n*/\n'))       .pipe(gulp.dest(config.distdir));   } 

every time above gulp task runs injects copyright each time adding new 1 every time. know how accomplish this?