File handling

Using the built-in os package.

Open file

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

open file.go: no such file or directory

Read into a slice of bytes:

data := make([]byte, 100)

count, err := file.Read(data)
if err != nil {
	log.Fatal(err)
}

fmt.Printf("read %d bytes: %q\n", count, data[:count])

Stats

func checkFileExists(filePath string) bool {
  if _, err := os.Stat(filePath); err != nil {
    if os.IsNotExist(err) {
      return false
    }
  }
  
  return true
}

exists = checkFileExists("my-path.txt")

Last modified time, size, and is directory.

stats, err = os.Stat("my-file.txt")
if err != nil {
  panic(err)
}

stats.ModTime()
stats.Size()
stats.IsDir()

Write file

Create or overwrite

Simple:

import "io/ioutil"

out_data = []byte("My file contents\n")
ioutil.Writefile("my-path.txt", out_data, 0644)

func handleError(err error) {
  if err != nil {
    panic(err)
  }
}

f, err = os.CreateFile("my-path.txt")
handleError(err)

defer f.Close()

f.Name()

f.WriteString("My file contents\n")

out_data := []bytes{"a", "b", "c", "\n"}
f.Write(out_data)

From Go docs - OpenFile.

package main

import (
	"log"
	"os"
)

func main() {
	f, err := os.OpenFile("notes.txt", os.O_RDWR|os.O_CREATE, 0755)
	if err != nil {
		log.Fatal(err)
	}
	if err := f.Close(); err != nil {
		log.Fatal(err)
	}
}

Append

From Go docs - OpenFile Append.

package main

import (
    "log"
    "os"
)

func main() {
    // If the file doesn't exist, create it, or append to the file
    f, err := os.OpenFile("access.log", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
    if err != nil {
        log.Fatal(err)
    }
    if _, err := f.Write([]byte("appended some data\n")); err != nil {
        log.Fatal(err)
    }
    if err := f.Close(); err != nil {
        log.Fatal(err)
    }
}

Based on SO top voted answer.

f, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0644)
if err != nil {
    panic(err)
}

defer f.Close()

if _, err = f.WriteString(text); err != nil {
    panic(err)
}

Directories

Create

os.MkDir("my-dir", os.ModePerm)
os.MkDirAll("my/nested/my-dir", os.ModePerm)

Delete

defer os.Remove("my-dir")
defer os.RemoveAll("my/nested/my-dir")

Working directory

os.Getwd()

Current process

exedir, _ = os.Executable()

If you do go run main.go the result will be a binary executable in a temp directory.

Contents

contents = ioutils.ReadDir(".")
for _, fi := range contents {
    fmt.Println(fi.Name(), fi.IsDir())
}