Append to a file in Go

Question

So I can read from a local file like so:

data, error := ioutil.ReadFile(name)

And I can write to a local file

ioutil.WriteFile(filename, content, permission)

But how can I append to a file? Is there a built in method?

Answer 1

If you also want to create the file

f, err := os.OpenFile(filename, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0600)

Answer 2

This answers works in Go1:

f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY, 0600)
if err != nil {
    panic(err)
}

defer f.Close()

if _, err = f.WriteString(text); err != nil {
    panic(err)
}

Answer 3

... I would use fmt.Fprintf, because accept a writer... and a connection or files will be a writer and easy to write in a way of string...

f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY, 0600)
if err != nil {
    panic(err)
}

defer f.Close()
fmt.Fprintf(f, "%s", text)

I hope this help!

Javier,

Answer 4

Figured it out

More info

f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY, 0644) 

n, err := f.WriteString(text) 

f.Close()

Answer 5

Go docs has a perfect example :

package main

import (
    "log"
    "os"
)

func main() {
    // If the file doesn't exist, create it, or append to the file
    f, err := os.OpenFile("access.log", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
    if err != nil {
        log.Fatal(err)
    }
    if _, err := f.Write([]byte("appended some data\n")); err != nil {
        log.Fatal(err)
    }
    if err := f.Close(); err != nil {
        log.Fatal(err)
    }
}