How to read a text file?

I'm trying to read "file.txt" and put the contents into a variable using Golang. Here is what I've tried...

package main

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

func main() {
	file, err := os.Open("file.txt")
	if err != nil {
		log.Fatal(err)
	}

	fmt.Print(file)
}

The file gets read successfully and the return from os.Open returns a type of *os.File

It depends on what you are trying to do.

file, err := os.Open("file.txt")
fmt.print(file)

The reason it outputs &{0xc082016240}, is because you are printing the pointer value of a file-descriptor (*os.File), not file-content. To obtain file-content, you may READ from a file-descriptor.

To read all file content(in bytes) to memory, ioutil.ReadAll

package main

import (
    "fmt"
    "io/ioutil"
    "os"
    "log"
)

func main() {
    file, err := os.Open("file.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err = file.Close(); err != nil {
            log.Fatal(err)
        }
    }()


  b, err := ioutil.ReadAll(file)
  fmt.Print(b)
}

But sometimes, if the file size is big, it might be more memory-efficient to just read in chunks: buffer-size, hence you could use the implementation of io.Reader.Read from *os.File

func main() {
	file, err := os.Open("file.txt")
	if err != nil {
		log.Fatal(err)
	}
    defer func() {
        if err = file.Close(); err != nil {
            log.Fatal(err)
        }
    }()


	buf := make([]byte, 32*1024) // define your buffer size here.

	for {
		n, err := file.Read(buf)

		if n > 0 {
			fmt.Print(buf[:n]) // your read buffer.
		}

		if err == io.EOF {
			break
		}
		if err != nil {
			log.Printf("read %d bytes: %v", n, err)
            break
		}
	}

}

Otherwise, you could also use the standard util package: bufio, try Scanner. A Scanner reads your file in tokens: separator.

By default, scanner advances the token by newline (of course you can customise how scanner should tokenise your file, learn from here the bufio test).

package main

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

func main() {
    file, err := os.Open("file.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err = file.Close(); err != nil {
            log.Fatal(err)
        }
    }()

    scanner := bufio.NewScanner(file)

  	for scanner.Scan() {             // internally, it advances token based on sperator
  		fmt.Println(scanner.Text())  // token in unicode-char
  		fmt.Println(scanner.Bytes()) // token in bytes

  	}
}

Lastly, I would also like to reference you to this awesome site: go-lang file cheatsheet. It encompassed pretty much everything related to working with files in go-lang, hope you'll find it useful.