Modify file in place (same dest) using Gulp.js and a globbing pattern

As you suspected, you are making this too complicated. The destination doesn't need to be dynamic as the globbed path is used for the dest as well. Simply pipe to the same base directory you're globbing the src from, in this case "sass":

gulp.src("sass/**/*.scss")
  .pipe(sass())
  .pipe(gulp.dest("sass"));

If your files do not have a common base and you need to pass an array of paths, this is no longer sufficient. In this case, you'd want to specify the base option.

var paths = [
  "sass/**/*.scss", 
  "vendor/sass/**/*.scss"
];
gulp.src(paths, {base: "./"})
  .pipe(sass())
  .pipe(gulp.dest("./"));

gulp.src("sass/**/*.scss")
  .pipe(sass())
  .pipe(gulp.dest(function(file) {
    return file.base;
  }));

Originally answer given here: https://stackoverflow.com/a/29817916/3834540.

I know this thread is old but it still shows up as the first result on google so I thought I might as well post the link here.

This is simpler than numbers1311407 has led on. You don't need to specify the destination folder at all, simply use .. Also, be sure to set the base directory.

gulp.src("sass/**/*.scss", { base: "./" })
    .pipe(sass())
    .pipe(gulp.dest("."));