Go by Example: Writing Files

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" "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()`
	`}`

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 .