gulp-inject-text

Install

npm install gulp-inject-text --save-dev

External

var gulp = require('gulp'),
   inject = require('gulp-inject-text');
gulp.task('lint', function() {
   return gulp.src('./html/*.html')
            .pipe(concat('mian.html'))
            .pipe(inject('./index.html'))  // inject(..,'<!--**-->')
            .pipe(rename('mian.html'))
            .pipe(gulp.dest('dist'));

  ...
  index.html
  ...
  <!-- inject-string -->
  ...
  ...