decimal to hex

dec-to-hex.go

package main

import (
	"bufio"
	"encoding/binary"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"

	"github.com/mattn/go-isatty"
)

func main() {
	args := os.Args
	writeAsBinary := false
	if len(args) == 2 {
		if args[1] == "bin" {
			writeAsBinary = true
		}
	}

	isattyIn := isatty.IsTerminal(os.Stdin.Fd())
	isattyOut := isatty.IsTerminal(os.Stdout.Fd())

	if isattyIn {
		fmt.Print("Enter text: ")
	}

	input := make([]byte, 0, 1024)
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	for scanner.Scan() {
		str := scanner.Text()
		if len(str) == 0 {
			continue
		}
		i, err := strconv.Atoi(str)
		check(err)
		if i >= 256 {
			log.Fatalln("value is bigger than 1 byte:", i)
		} else {
			input = append(input, byte(i))
		}
	}

	if err := scanner.Err(); err != nil {
		fmt.Fprintln(os.Stderr, "reading standard input:", err)
	}

	// if output is piped to with bin flag
	if !isattyOut && writeAsBinary {
		err := binary.Write(os.Stdout, binary.LittleEndian, input)
		check(err)
		if err != nil {
			os.Exit(1)
		} else {
			os.Exit(0)
		}
	}

	var b strings.Builder
	for i, v := range input {
		_, err := b.WriteString(fmt.Sprintf("%02X ", v))
		check(err)
		if (i+1)%16 == 0 {
			fmt.Println(b.String())
			b.Reset()
		}
	}
	fmt.Println(b.String())
}

func check(e error) {
	if e != nil {
		log.Fatalln(e)
	}
}