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Learning Test-Driven Development with Go

I/O Interactions with "io" and "os" Packages

Explore the io and os packages in Go to understand file creation, reading, writing, copying, and managing environment variables. This lesson helps you grasp key interfaces like io.Reader and io.Writer and their practical use in I/O operations within Go.

We'll cover the following...

os and io packages

Let’s start with an example to illustrate what the various functions do.

Go (1.18.2)
package main
import (
	"bytes"
	"fmt"
	"io"
	"os"
)
func main() {
	// create a file to be written
	out, err := os.Create("output/result.txt")
	if err != nil {
		panic(err)
	}
	defer out.Close()
	// copy bytes to the previously created file
	n, _ := io.Copy(out, bytes.NewReader([]byte("simple text to be written")))
	fmt.Printf("bytes written: %d\n", n)
}

This above code creates a new file and writes some content to it. The os.Create method creates a file at the specified path if one doesn’t exist. If the file already exists, it’ll be truncated. If the file is created, its permission mode is 0666 (read and write).

The io.Copy method simply copies from a source to a destination until either an EOF error is encountered or another error occurs.

io package

The io package provides us with useful functions and values we can use to manage byte data types. Some values that could be managed are lists of bytes, streams of bytes, or individual bytes. Now, let’s focus on three methods: io.Read, io.Write, and io.Copy. ...