Writing buffer to file doesn't return error, so why is file empty afterwords?

Question

I'm trying to read all standard input and write it to a file. It's writing nothing to the file provided. Why is it not working?

package main

import (
    "os"
    "bytes"
    "fmt"
    "bufio"
)

func main() {
    fn := os.Args[1]
    var input bytes.Buffer
    scanner := bufio.NewScanner(os.Stdin)

    for scanner.Scan() {
        fmt.Fprintf(&input, scanner.Text())
        fmt.Fprintf(&input, "\n")
    }   

    fi, _ := os.Open(fn)
    defer fi.Close()

    fi.Write(input.Bytes())
}

And then...

touch writetothis.txt
echo "input text" | go run main.go writetothis.txt
# writetothis.txt is empty

Answer 1

Open opens a file in read-only mode.
Refer to documentation: https://golang.org/pkg/os/#Open

Instead, use OpenFile.

Also, always check for errors whenever you code. It'll save you at least weeks of work-hours in your lifetime.

Here is a working code:

package main

import (
    "bufio"
    "bytes"
    "fmt"
    "os"
)

func main() {
    fn := os.Args[1]
    var input bytes.Buffer
    scanner := bufio.NewScanner(os.Stdin)

    for scanner.Scan() {
        fmt.Fprintf(&input, scanner.Text())
        fmt.Fprintf(&input, "\n")
    }

    fmt.Println(input.Bytes())
    fi, err := os.OpenFile(fn, os.O_RDWR|os.O_CREATE, 0755)

    if err != nil {
        fmt.Println("Error with Open()",err)
    }
    defer fi.Close()

    n, err := fi.Write(input.Bytes())
    if err != nil {
        fmt.Println("Error with Write()", err)
    }
    fmt.Println("Bytes written to file: ",n)
}