package main

import (
    "io"
    "fmt"
    "os"
)

// copy file using os package
func copyFileUsingOsPackage(src, dst string) error {
    bytesRead, err := os.ReadFile(src)
    if err != nil {
        return err
    }

    return os.WriteFile(dst, bytesRead, 0644)
}

// copy file using io package
func copyFileUsingIoPackage(src, dst string) (int64, error) {
        source, err := os.Open(src)
        if err != nil {
                return 0, err
        }
        defer source.Close()

        destination, err := os.Create(dst)
        if err != nil {
                return 0, err
        }
        defer destination.Close()
        
        nBytes, err := io.Copy(destination, source)
        
        return nBytes, err
}

func main() {
    src := "/tmp/file-src.txt"
    dst := "/tmp/file-dst.txt"

    n, err := copyFileUsingIoPackage(src, dst)

    if err != nil {
        panic(err)
    }

    fmt.Printf("Copied %d bytes", n)
    fmt.Println()

    err = copyFileUsingOsPackage(src, dst)

    if err != nil {
        panic(err)
    }
}