How to write the output of this statement into a file in Golang

Question

I'm trying to write the output of the statement below into a text file but I can't seem to find out if there is a printf function that writes directly to a text file. For example if the code below produces the results [5 1 2 4 0 3] I would want to read this into a text file for storage and persistence. Any ideas please?

The code I want to goto the text file:

//choose random number for recipe
r := rand.New(rand.NewSource(time.Now().UnixNano()))
i := r.Perm(5)
fmt.Printf("%v\n", i)
fmt.Printf("%d\n", i[0])
fmt.Printf("%d\n", i[1])

Users who are watching this questing may be interested in **How to write log to file in Go** https://stackoverflow.com/questions/19965795/how-to-write-log-to-file — Arun, Apr 12 '20 at 00:26

syntagma · Accepted Answer · 2017-08-08T12:16:28.683

27

You can use fmt.Fprintf together with an io.Writer, which would represent a handle to your file.

Here is a simple example:

func check(err error) {
    if err != nil {
        panic(err)
    }
}

func main() {
    f, err := os.Create("/tmp/yourfile")
    check(err)
    defer f.Close()

    w := bufio.NewWriter(f)
    //choose random number for recipe
    r := rand.New(rand.NewSource(time.Now().UnixNano()))
    i := r.Perm(5)

    _, err = fmt.Fprintf(w, "%v\n", i)
    check(err)
    _, err = fmt.Fprintf(w, "%d\n", i[0])
    check(err)
    _, err = fmt.Fprintf(w, "%d\n", i[1])
    check(err)
    w.Flush()
}

More ways of writing to file in Go are shown here.

Note that I have used panic() here just for the sake of brevity, in the real life scenario you should handle errors appropriately (which in most cases means something other than exiting the program, what panic() does).

edited Aug 08 '17 at 12:16

answered Feb 11 '16 at 07:39

syntagma

23,346
16
78
134

Interesting, would there be an example i could follow? – Tbalz Feb 11 '16 at 07:40
I may nitpick here, but I think it would be nice to mention for those who are not familiar with Go that panicking in those circumstances may not be appropriate in a real case scenario. – basgys Feb 11 '16 at 08:12
1

@basgys Sure, I have added it. – syntagma Feb 11 '16 at 09:14

score 5 · Answer 2 · answered Feb 11 '16 at 07:52

This example will write the values into the output.txt file.

package main

import (
    "bufio"
    "fmt"
    "math/rand"
    "os"
    "time"
)

func main() {

    file, err := os.OpenFile("output.txt", os.O_WRONLY|os.O_CREATE, 0666)
    if err != nil {
        fmt.Println("File does not exists or cannot be created")
        os.Exit(1)
    }
    defer file.Close()

    w := bufio.NewWriter(file)
    r := rand.New(rand.NewSource(time.Now().UnixNano()))
    i := r.Perm(5)
    fmt.Fprintf(w, "%v\n", i)

    w.Flush()
}

score 4 · Answer 3 · answered Feb 11 '16 at 07:47

4

Use os package to create file and then pass it to Fprintf

file, fileErr := os.Create("file")
if fileErr != nil {
    fmt.Println(fileErr)
    return
}
fmt.Fprintf(file, "%v\n", i)

This should write to file.

answered Feb 11 '16 at 07:47

sfault

693
5
9

How to write the output of this statement into a file in Golang

3 Answers3