Read a file into a variable in Go (Golang)

Overview

There are various ways of reading a file into a variable in golang. Here are some of the ways

• Using ReadFile function provided by the ioutil package

• Using os.Open and then using bytes.Buffer

• Using os.Open and then using strings.Builder

.Also, note reading the entire file into a variable only makes sense if you are reading a small file. If the file is large then it makes sense to read it line by line. Refer to this article for the same.

https://golangbyexample.com/read-large-file-line-by-line-go/

Note: Before trying out examples in this tutorial, please create a file named test.png at the location from which you will be running the program

Using ReadFile function provided by the ioutil package

https://golang.org/pkg/io/ioutil/#ReadFile

Below is the program for the same

package main

import (
    "fmt"
    "io/ioutil"
)

func main() {
    fileBytes, err := ioutil.ReadFile("test.png")
    if err != nil {
        panic(err)
    }
    fileString := string(fileBytes)
    fmt.Println(fileString)
}

Output

Some Garbage Output depending upon the file

Using os.Open and then using bytes.Buffer

https://golang.org/pkg/bytes/#Buffer

Below is the program for the same

package main

import (
	"bytes"
	"fmt"
	"log"
	"os"
)

func main() {
	file, err := os.Open("test.png")
	if err != nil {
		log.Fatalf("Error while opening file. Err: %s", err)
	}
	defer file.Close()

	fileBuffer := new(bytes.Buffer)
	fileBuffer.ReadFrom(file)
	fileString := fileBuffer.String()

	fmt.Print(fileString)
}

Output

Some Garbage Output depending upon the file

Using os.Open and then using strings.Builder

https://golang.org/pkg/strings/#Builder

Below is the program for the same

package main

import (
	"bytes"
	"fmt"
	"log"
	"os"
)

func main() {
	file, err := os.Open("test.png")
	if err != nil {
		log.Fatalf("Error while opening file. Err: %s", err)
	}
	defer file.Close()

	fileBuffer := new(bytes.Buffer)
	fileBuffer.ReadFrom(file)
	fileString := fileBuffer.String()

	fmt.Print(fileString)
}

Output

Some Garbage Output depending upon the file

Also, check out our Golang advance tutorial Series – Golang Advance Tutorial