Append to a file in Go
File IoGoFile Io Problem Overview
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?
File Io Solutions
Solution 1 - File Io
This answers works in Go1:
f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0600)
if err != nil {
panic(err)
}
defer f.Close()
if _, err = f.WriteString(text); err != nil {
panic(err)
}
Solution 2 - File Io
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)
}
}
Solution 3 - File Io
Figured it out
f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY, 0644)
n, err := f.WriteString(text)
f.Close()
Solution 4 - File Io
... 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,
Solution 5 - File Io
If you also want to create the file
f, err := os.OpenFile(filename, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0600)
Solution 6 - File Io
f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0644)
if err != nil {
panic(err)
}
defer f.Close()
if _, err = f.WriteString(text); err != nil {
panic(err)
}
Made a slight change from the one provided in the golang site by adding flags to the os.OpenFile function which by default will only allow reading of a file and not editing amongst other features.
Solution 7 - File Io
Let's say you want to add the contents of filecurrent to the file all, then below code is working:
func updateTrx() {
var err error
var f *os.File
// If the file doesn't exist, create it, or append to the file
if f, err = os.OpenFile("all.csv", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644); err != nil {
log.Fatal(err)
}
defer func() {
if err := f.Close(); err != nil {
log.Fatal("error", err)
}
}()
var current *os.File
if current, err = os.OpenFile("current.csv", os.O_RDONLY, 0); err != nil {
log.Fatal("error", err)
}
defer func() {
if err := current.Close(); err != nil {
log.Fatal("error", err)
}
}()
if fileBytes, err := ioutil.ReadAll(current); err != nil {
log.Fatal("error", err)
} else {
if _, err := f.Write([]byte(fileBytes)); err != nil {
log.Fatal(err)
}
}
}