A terminal utility for formatting JSON files written in Go

main.go

// 1. Get the path for our input file from
//    the command line arguments
// 2. Check if the input file is readable and contains
//    valid JSON
// 3. Format the contents of the file
// 4. Save formatted JSON to another file
// 5. Compile our binary

package main

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"os"
)

// A function to check if a string is valid JSON
// src: https://stackoverflow.com/a/22129435 (modified)
func isJSON(s string) bool {
	var js map[string]interface{}
	return json.Unmarshal([]byte(s), &js) == nil

}

func FileExists(name string) (bool, error) {
	_, err := os.Stat(name)
	if err == nil {
		return true, nil
	}
	if errors.Is(err, os.ErrNotExist) {
		return false, nil
	}
	return false, err
}

// A function to pretty print JSON strings
// src: https://stackoverflow.com/a/36544455
func jsonPrettyPrint(in string) string {
	var out bytes.Buffer
	err := json.Indent(&out, []byte(in), "", "\t")
	if err != nil {
		return in
	}
	return out.String()
}

func main() {
	// Get the arguments passed to our program
	arguments := os.Args[1:]

	// Check that at least 1 argument was passed
	if len(arguments) < 1 {
		// Display error message and exit the program
		fmt.Println("Missing required argument")
		fmt.Println("Usage: ./prettyJson input_file.json")
		return
	}

	// Call FileExists function with the file path
	exists, err := FileExists(arguments[0])

	// Check the result
	if exists != true {
		fmt.Println("Sorry the file", arguments[0], "does not exist!")
		return
	}
	if err != nil {
		fmt.Println("Error:", err)
		return
	}

	raw, err := os.ReadFile(arguments[0]) // just pass the file name
	if err != nil {
		fmt.Print(err)
	}

	// convert the files contents to string
	contents := string(raw)

	// check if the string is valid json
	if contents == "" || isJSON(contents) != true {
		fmt.Println("Invalid or empty JSON file")
		return
	}

	// print the formatted string; this output can be piped to an output file
	// no prefix and indenting with 4 spaces
	formatted := jsonPrettyPrint(contents)

	// Display the formatted string
	fmt.Println(formatted)
}