Write Files in Go

Introduction

This lab aims to test your ability to write files in Go. You will learn how to write a string or bytes into a file and how to use buffered writers.

Writing Files

You need to write a Go program that writes a string and bytes into a file and uses buffered writers.

• The program should write a string and bytes into a file.
• The program should use buffered writers.

## Try running the file-writing code.
$ go run writing-files.go
wrote 5 bytes
wrote 7 bytes
wrote 9 bytes

## Then check the contents of the written files.
$ cat /tmp/dat1
hello
go
$ cat /tmp/dat2
some
writes
buffered

## Next we'll look at applying some of the file I/O ideas
## we've just seen to the `stdin` and `stdout` streams.

There is the full code below:

// Writing files in Go follows similar patterns to the
// ones we saw earlier for reading.

package main

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

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

func main() {

    // To start, here's how to dump a string (or just
    // bytes) into a file.
    d1 := []byte("hello\ngo\n")
    err := os.WriteFile("/tmp/dat1", d1, 0644)
    check(err)

    // For more granular writes, open a file for writing.
    f, err := os.Create("/tmp/dat2")
    check(err)

    // It's idiomatic to defer a `Close` immediately
    // after opening a file.
    defer f.Close()

    // You can `Write` byte slices as you'd expect.
    d2 := []byte{115, 111, 109, 101, 10}
    n2, err := f.Write(d2)
    check(err)
    fmt.Printf("wrote %d bytes\n", n2)

    // A `WriteString` is also available.
    n3, err := f.WriteString("writes\n")
    check(err)
    fmt.Printf("wrote %d bytes\n", n3)

    // Issue a `Sync` to flush writes to stable storage.
    f.Sync()

    // `bufio` provides buffered writers in addition
    // to the buffered readers we saw earlier.
    w := bufio.NewWriter(f)
    n4, err := w.WriteString("buffered\n")
    check(err)
    fmt.Printf("wrote %d bytes\n", n4)

    // Use `Flush` to ensure all buffered operations have
    // been applied to the underlying writer.
    w.Flush()

}

Summary

In this lab, you learned how to write a string or bytes into a file and how to use buffered writers in Go.