// filecopy.go
package main
​
import (
    "fmt"
    "io"
    "os"
)
​
func main() {
    CopyFile("target.txt", "source.txt")
    fmt.Println("Copy done!")
}
​
func CopyFile(dstName, srcName string) (written int64, err error) {
    src, err := os.Open(srcName)
    if err != nil {
        return
    }
    defer src.Close()
​
    dst, err := os.Create(dstName)
    if err != nil {
        return
    }
    defer dst.Close()
​
    return io.Copy(dst, src)
}