Copy file

In Go the os.Rename func moves a file from one location to another. But if we want to copy the file, we cannot just move it.

With ioutil, we can read in the contents of a file (with ReadAll). Then we can write the copy to a new location. This logic can be placed in a reusable func.

Copy example

Here we have a main func that begins with 2 local variables. We must specify a valid input path (the source) and output path (the target).

Part 1 We open an input file with the os.Open func. We just ignore errors, but these could be checked.

Part 2 We read in the data from the file with ioutil.ReadAll. Again we just ignore errors.

Part 3 We call ioutil.WriteFile to write the data to a new location—the target location for the copy.

package main

import (
    "fmt"
    "io/ioutil"
    "os"
)

func main() {
    inputPath := `C:\programs\file.txt`
    outputPath := `C:\programs\copy.txt`

    // Part 1: open input file.
    inputFile, _ := os.Open(inputPath)

    // Part 2: call ReadAll to get contents of input file.
    data, _ := ioutil.ReadAll(inputFile)

    // Part 3: write data to copy file.
    ioutil.WriteFile(outputPath, data, 0)
    fmt.Println("DONE")
}
DONE

Notes, copying

When we want to copy a file, we cannot just call os.Rename as the original is deleted. Instead, we can use helpful methods from ioutil.

file.txt: 60 bytes
copy.txt: 60 bytes

Often it is important to copy files for deployment of projects (like websites or applications). With the code here, we can copy files without deleting the originals.