Adjust a bunch of JSON files in a folder.

main.go

package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"os"
)

// User struct stores user data.
type User struct {
	Name   string
	ID     int
	Sshkey string
	Shell  string
	Group  string
}

var (
	maxSize  = int64(4096)
	theDir   = "/Users/darron/Desktop/files-for-golang"
	newShell = "/bin/evilbash"
)

func getFiles() []string {
	var finalList []string
	files, err := ioutil.ReadDir(theDir)
	if err != nil {
		log.Fatal("Oh boy - something went wrong.")
	}

	// Get the details on each file.
	for _, theFile := range files {
		fileName := theFile.Name()
		fileSize := theFile.Size()

		if fileSize > maxSize {
			log.Printf("File '%s' is too big: '%d'", fileName, fileSize)
			continue
		}
		finalList = append(finalList, fileName)
	}
	return finalList
}

func rewriteFile(f string) {

	filePath := fmt.Sprintf("%s/%s", theDir, f)

	fileContents, err := ioutil.ReadFile(filePath)
	if err != nil {
		log.Println("There was an error reading the file.")
	}

	theUser := User{}

	// For each file - encode to JSON data structure.
	json.Unmarshal(fileContents, &theUser)

	// Change the shell to newShell
	theUser.Shell = newShell

	// Convert back to a string.
	newString, err := json.Marshal(&theUser)
	if err != nil {
		log.Print("There was an error with the new JSON.")
	}

	// Save updated json to each file.
	fileWriteErr := ioutil.WriteFile(filePath, newString, os.FileMode(0640))
	if fileWriteErr != nil {
		log.Println("There was an error writing the file.")
	}
}

func main() {
	// Get all files.
	files := getFiles()

	// Rewrite them all.
	for _, fileName := range files {
		rewriteFile(fileName)
	}
}