Go – How to write into a file in go

Here, We will see how to write into a file in go. We can do it by using either WriteString() or WriteAt() or Write() or WriteFile() function in os package in go golang.

WriteString() function

Function prototype:

func (f *File) WriteString(str string) (n int, err error)

Input Parameter:

str : file name

WriteString() function writes the string into file.

Return value:

WriteString() function in os package returns 
the number of bytes written and an error, if any.

Example with code:

package main

import (
  "fmt"
  "os"
  "log"
)

func main() {

  file_name := "/Users/hello.go"

  file, err := os.Create(file_name)

  if err != nil {

    log.Fatal(err)

    os.Exit(-1)

  }

  var bytes int

  bytes, err = file.WriteString("Hello Go")


  if err != nil {

    log.Fatal(err)

    os.Exit(-1)

  }

  fmt.Println("Bytes Written in file: ", bytes)

  defer file.Close()
}

Output:

$ sudo go run sample.go
Bytes Written in file: 8

$ ls -lrt hello.go
-rw-r--r-- 1 root staff 8 May 5 20:22 hello.go

$cat hello.go
Hello Go

Write() function

Function prototype:

func (f *File) Write(b []byte) (n int, err error)

b: String to be written in byte array

Write() writes len(b) bytes to the File.

Return value:

Write() function in os package returns
the number of bytes written and an error, if any.

Example with code:

package main

import (
  "fmt"
  "os"
  "log"
)

func main() {

  file_name := "/Users/hello.go"

  file, err := os.Create(file_name)

  if err != nil {

    log.Fatal(err)

    os.Exit(-1)

  }


  str := []byte("Hello Go")

  var bytes int

  bytes, err = file.Write(str)


  if err != nil {

    log.Fatal(err)

    os.Exit(-1)

  }

  fmt.Println("Bytes Written in file: ", bytes)

  defer file.Close()
}

Output:

$ sudo go run sample.go
Bytes Written in file: 8

$ ls -lrt hello.go
-rw-r--r-- 1 root staff 8 May 5 20:22 hello.go

$cat hello.go
Hello Go

WriteFile() Function

Function prototype:

func WriteFile(filename string, data []byte, perm os.FileMode) error

Return value:

WriteFile() function in ioutil package returns
an error, if any.

Example with code:

package main

import (
  "io/ioutil"
  "log"
)

func main() {

  file_name := "/Users/hello.go"

  data := []byte("Hello go")

  err := ioutil.WriteFile(file_name, data, 0644)

  if err != nil {

    log.Fatal(err)

  }
}

Output:

$ sudo go run sample.go

$ ls -lrt hello.go
-rw-r--r-- 1 root staff 5 May 6 19:05 hello.goo

$cat hello.go
Hello

To learn more about golang, Please refer given below link:

https://www.techieindoor.com/go-lang-tutorial/

References:

https://golang.org/doc/
https://golang.org/pkg/