Little Go tool to flatten JSON input

flattenjson.go

// Flatten JSON input
//
// Example:
//
// $ echo '{"user":"Ben","ints":[true,false,null],"sub":{"x":1,"y":2}}' | go run flattenjson.go
// _.ints[0] = true
// _.ints[1] = false
// _.ints[2] = null
// _.sub.x = 1
// _.sub.y = 2
// _.user = "Ben"

package main

import (
	"encoding/json"
	"fmt"
	"os"
	"sort"
)

func main() {
	decoder := json.NewDecoder(os.Stdin)
	var obj interface{}
	err := decoder.Decode(&obj)
	if err != nil {
		fmt.Fprintf(os.Stderr, "input is not valid JSON: %s\n", err)
		os.Exit(1)
	}
	flatten(obj, "_")
}

func flatten(obj interface{}, prefix string) {
	switch obj := obj.(type) {
	case bool:
		fmt.Printf("%s = %t\n", prefix, obj)
	case float64:
		fmt.Printf("%s = %g\n", prefix, obj)
	case string:
		fmt.Printf("%s = %q\n", prefix, obj)
	case []interface{}:
		for i, v := range obj {
			flatten(v, fmt.Sprintf("%s[%d]", prefix, i))
		}
	case map[string]interface{}:
		keys := make([]string, 0, len(obj))
		for k := range obj {
			keys = append(keys, k)
		}
		sort.Strings(keys)
		for _, k := range keys {
			flatten(obj[k], fmt.Sprintf("%s.%s", prefix, k))
		}
	default:
		fmt.Printf("%s = null\n", prefix)
	}
}