io/ioutil

• func ReadAll(r io.Reader) ([]byte, error):ReadAll reads from r until an error or EOF and returns the data it read. A successful call returns err == nil, not err == EOF. Because ReadAll is defined to read from src until EOF, it does not treat an EOF from Read as an error to be reported.

package main

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

func main() {
    r := strings.NewReader("Go is a general-purpose language designed with systems programming in mind.")

    b, err := ioutil.ReadAll(r)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(string(b))

}

• func ReadFile(filename string) ([]byte, error) ReadFile reads the file named by filename and returns the contents. A successful call returns err == nil, not err == EOF. Because ReadFile reads the whole file, it does not treat an EOF from Read as an error to be reported.

package main

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

func main() {
    content, err := ioutil.ReadFile("testdata/hello")
    if err != nil {
        log.Fatal(err)
    }

    fmt.Printf("File contents: %s", content)

}

• func ReadDir(dirname string) ([]os.FileInfo, error) ReadDir reads the directory named by dirname and returns a list of directory entries sorted by filename. 只显示第一层的所有文件和文件夹，不包括.

package main

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

func main() {
    files, err := ioutil.ReadDir(".")
    if err != nil {
        log.Fatal(err)
    }

    for _, file := range files {
        fmt.Println(file.Name())
    }
}

• func WriteFile(filename string, data []byte, perm os.FileMode) error WriteFile writes data to a file named by filename. If the file does not exist, WriteFile creates it with permissions perm; otherwise WriteFile truncates it before writing.

package main

import (
    "io/ioutil"
    "log"
)

func main() {
    message := []byte("Hello, Gophers!")
    err := ioutil.WriteFile("testdata/hello", message, 0644)
    if err != nil {
        log.Fatal(err)
    }
}