Go copy file
last modified April 11, 2024
In this article we show how to copy a file in Golang. We show three ways to copy a file in Go.
We use the ioutil.ReadFile, ioutil.WriteFile,
io.Copy, File.Read, File.Write functions
to copy files.
$ go version go version go1.22.2 linux/amd64
We use Go version 1.22.2.
Go copy file example
In the first example, we use the functions from the ioutil package.
package main
import (
"io/ioutil"
"log"
)
func main() {
src := "words.txt"
dest := "words2.txt"
bytesRead, err := ioutil.ReadFile(src)
if err != nil {
log.Fatal(err)
}
err = ioutil.WriteFile(dest, bytesRead, 0644)
if err != nil {
log.Fatal(err)
}
}
The ioutil.ReadFile reads the specified file and returns the
contents in a slice of bytes. The ioutil.WriteFile writes the
specified slice of bytes into the destination file.
Go copy file example II
In the second example, we use the io.Copy function to copy a file.
package main
import (
"io"
"log"
"os"
)
func main() {
src := "words.txt"
dst := "words2.txt"
fin, err := os.Open(src)
if err != nil {
log.Fatal(err)
}
defer fin.Close()
fout, err := os.Create(dst)
if err != nil {
log.Fatal(err)
}
defer fout.Close()
_, err = io.Copy(fout, fin)
if err != nil {
log.Fatal(err)
}
}
We open the source file with os.Open and create the destination
file with os.Create; the handles to these two files are passed to
the io.Copy function.
Go copy file example III
The File.Read reads up to len(b) bytes from the file,
where b is a slice of bytes. The File.Write function
writes the provided slice of bytes to the destination file.
package main
import (
"io"
"log"
"os"
)
func main() {
src := "words.txt"
dst := "words2.txt"
buf := make([]byte, 1024)
fin, err := os.Open(src)
if err != nil {
log.Fatal(err)
}
defer fin.Close()
fout, err := os.Create(dst)
if err != nil {
log.Fatal(err)
}
defer fout.Close()
for {
n, err := fin.Read(buf)
if err != nil && err != io.EOF {
log.Fatal(err)
}
if n == 0 {
break
}
if _, err := fout.Write(buf[:n]); err != nil {
log.Fatal(err)
}
}
}
We create a buffer of 1024 bytes. In a for loop, we read the bytes from the
source file into the buffer and write the buffer into the destination file. When
there is no more data to read, the File.Read function returns 0 and
we break the loop.
Source
In this article we have copied files in Golang.
Author
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