Go by Example: Writing Files

Writing files in Go follows similar patterns to the ones we saw earlier for reading.
	package main
	import ( "bufio" "fmt" "io/ioutil" "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 := ioutil.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") 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") fmt.Printf("wrote %d bytes\n", n4)
Use `Flush` to ensure all buffered operations have been applied to the underlying writer.	w.Flush()
	}

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.

Next example: Line Filters.