golang-create-read-write-delete-file.go

package main

import (
	"fmt"
	"io"
	"os"
)

var path = "/Users/novalagung/Documents/temp/test.txt"

func main() {
	createFile()
	writeFile()
	readFile()
	deleteFile()
}

func createFile() {
	// detect if file exists
	var _, err = os.Stat(path)

	// create file if not exists
	if os.IsNotExist(err) {
		var file, err = os.Create(path)
		if isError(err) { return }
		defer file.Close()
	}

	fmt.Println("==> done creating file", path)
}

func writeFile() {
	// open file using READ & WRITE permission
	var file, err = os.OpenFile(path, os.O_RDWR, 0644)
	if isError(err) { return }
	defer file.Close()

	// write some text line-by-line to file
	_, err = file.WriteString("halo\n")
	if isError(err) { return }
	_, err = file.WriteString("mari belajar golang\n")
	if isError(err) { return }

	// save changes
	err = file.Sync()
	if isError(err) { return }

	fmt.Println("==> done writing to file")
}

func readFile() {
	// re-open file
	var file, err = os.OpenFile(path, os.O_RDWR, 0644)
	if isError(err) { return }
	defer file.Close()

	// read file, line by line
	var text = make([]byte, 1024)
	for {
		_, err = file.Read(text)
		
		// break if finally arrived at end of file
		if err == io.EOF {
			break
		}
		
		// break if error occured
		if err != nil && err != io.EOF {
			isError(err)
			break
		}
	}
	
	fmt.Println("==> done reading from file")
	fmt.Println(string(text))
}

func deleteFile() {
	// delete file
	var err = os.Remove(path)
	if isError(err) { return }

	fmt.Println("==> done deleting file")
}

func isError(err error) bool {
	if err != nil {
		fmt.Println(err.Error())
	}

	return (err != nil)
}

This is a bit buggy. Your defer file.Close() call will never be called if os.Create fails because you are calling os.Exit and according to documentation exit doesn't call any deferred calls.

Thank you!

@milosgajdos83 :)

@milosgajdos83 Would that matter though? Because if the program is exiting, it doesn't need to run the deferred functions. Either way, he could've just used fmt.Fatal().

Helpful for me

Like some of you have already suggested, this approach has some bugs. Remember that "defers will not be run when using os.Exit" (https://gobyexample.com/exit).
I fix that issue here: https://gist.github.com/joe94/9725e84392654fbb68ff16053ea6d5bf

@milosgajdos83 @joe94 thanks for the responses. I just modified the file for better logging. also all os.Exit() statements are removed now

cool!

Hey, this came in handy. I'd rather read code than words explaining it. thanks!

thanks !

I am getting " undefine: isError"

Helped me, thanks.

Suwun cak noval

Thanks mate!

Did you know that you can also use the ioutil functions?

import "io/ioutil"

// read file
bytes,err:= ioutil.ReadFile(filename)
if err!=nil{
panic(err)
}
mystringdata:=string(bytes[:])

//write file
err:=ioutil.WriteFile("myfile.txt",[]byte("write this to file"),0644)
if err!=nil{
panic(err)
}

I think it has an issue in createFile() function. Because I tested the code without test.txt file in the path but there isn't "test.txt" file after running the code.