# 7.5 Files

File is must-have object in every single computer device, and web applications also have many usage with files. In this section, we're going to learn how to operate files in Go.

## Directories

Most of functions of file operations is in package `os`, here are some functions about directories:

- func Mkdir(name string, perm FileMode) error

	Create directory with `name`, `perm` is permission, like 0777.
	
- func MkdirAll(path string, perm FileMode) error

	Create multiple directories according to `path`, like `astaxie/test1/test2`.
	
- func Remove(name string) error

	Remove directory with `name`, it returns error if it's not directory or not empty.

- func RemoveAll(path string) error

	Remove multiple directories according to `path`, it will not be deleted if `path` is a single path. 

Code sample:

	package main

	import (
		"fmt"
		"os"
	)
	
	func main() {
		os.Mkdir("astaxie", 0777)
		os.MkdirAll("astaxie/test1/test2", 0777)
		err := os.Remove("astaxie")
		if err != nil {
			fmt.Println(err)
		}
		os.RemoveAll("astaxie")
	}

## Files

### Create and open files

Two functions to create files:

- func Create(name string) (file *File, err Error)

	Create file with `name` and return a file object with permission 0666 and read-writable.

- func NewFile(fd uintptr, name string) *File
	
	Create file and return a file object.


Two functions to open files:

- func Open(name string) (file *File, err Error)

	Open file with `name` with read-only permission, it calls `OpenFile` underlying.

- func OpenFile(name string, flag int, perm uint32) (file *File, err Error)	

	Open file with `name`, `flag` is open mode like read-only, read-write, `perm` is permission.

### Write files

Functions for writing files:

- func (file *File) Write(b []byte) (n int, err Error)

	Write byte type content to file.

- func (file *File) WriteAt(b []byte, off int64) (n int, err Error)

	Write byte type content to certain position of file.

- func (file *File) WriteString(s string) (ret int, err Error)

	Write string to file.
	
Code sample:

	package main

	import (
		"fmt"
		"os"
	)
	
	func main() {
		userFile := "astaxie.txt"
		fout, err := os.Create(userFile)		
		if err != nil {
			fmt.Println(userFile, err)
			return
		}
		defer fout.Close()
		for i := 0; i < 10; i++ {
			fout.WriteString("Just a test!\r\n")
			fout.Write([]byte("Just a test!\r\n"))
		}
	}

### Read files

Functions for reading files:

- func (file *File) Read(b []byte) (n int, err Error)

	Read data to `b`.

- func (file *File) ReadAt(b []byte, off int64) (n int, err Error)

	Read data from position `off` to `b`.

Code sample:

	package main

	import (
		"fmt"
		"os"
	)
	
	func main() {
		userFile := "asatxie.txt"
		fl, err := os.Open(userFile)		
		if err != nil {
			fmt.Println(userFile, err)
			return
		}
		defer fl.Close()
		buf := make([]byte, 1024)
		for {
			n, _ := fl.Read(buf)
			if 0 == n {
				break
			}
			os.Stdout.Write(buf[:n])
		}
	}

### Delete files

Go uses same function for removing files and directories:

- func Remove(name string) Error

	Remove file or directory with `name`.( ***`name` ends with `/` means directory*** )

## Links

- [Directory](preface.md)
- Previous section: [Templates](07.4.md)
- Next section: [Strings](07.6.md)