recursively measuring the size of the a directory / subdirectory

dir_size.go

package main 

import "filepath"
import "os"

func main() {
    dirSize("path/to/folder")
}

func dirSize(path string) (int64, error) {
	var size int64
	err := filepath.Walk(path, func(_ string, info os.FileInfo, err error) error {
		if !info.IsDir() {
			size += info.Size()
		}
		return err
	})
	return size, err
}