package main

import (
	"bufio"
	"io"
	"log"
	"os"
	"os/exec"
)

func doWrite(aContent string) error {
	f, err := os.OpenFile("content.txt", os.O_WRONLY|os.O_CREATE, 0600)
	if err != nil {
		return err
	}
	defer f.Close()

	_, err = f.WriteString(aContent + "\n")
	return err
}

func doRead() (string, error) {
	f, err := os.Open("content.txt")
	if err != nil {
		return "", err
	}
	defer f.Close()

	buf := bufio.NewReader(f)
	content := ""
	doRead := true
	for doRead {
		line, err := buf.ReadString('\n')
		if err != nil {
			if err != io.EOF {
				return "", err
			}
			doRead = false
		}
		content = content + line
	}

	return content, nil
}

func main() {
	// show go version first:
	cmd := exec.Command("go", "version")
	version, err := cmd.CombinedOutput()
	if err != nil {
		log.Fatalf("%s", err)
	}
	log.Printf("%s", string(version))

	// first write a long string to "content.txt"
	if err = doWrite("abcdefghijklmnopqrstuvwxyz"); err != nil {
		log.Fatalf("doWrite error (1): %s", err)
	}

	// read and show the contents:
	content, err := doRead()
	if err != nil {
		log.Fatalf("doRead error (1): %s", err)
	}
	log.Printf("doRead content (1): %q", content)

	// now write a short string again to "content.txt"
	if err = doWrite("abc"); err != nil {
		log.Fatalf("doWrite error (2): %s", err)
	}

	// read and show the contents:
	content, err = doRead()
	if err != nil {
		log.Fatalf("doRead error (2): %s", err)
	}
	log.Printf("doRead content (2): %q", content)
}