go打开文件模式

O_RDONLY  // open the file read-only.
O_WRONLY  // open the file write-only.
O_RDWR    // open the file read-write.
// The remaining values may be or'ed in to control behavior.
O_APPEND  // append data to the file when writing.
O_CREATE  // create a new file if none exists.
O_EXCL    // used with O_CREATE, file must not exist.
O_SYNC    // open for synchronous I/O.
O_TRUNC   // truncate regular writable file when opened.

1.读全部

import (
    "errors"
	"fmt"
	"io/ioutil"
    )
f,err:=ioutil.ReadFile("./log.text")   // ReadFile 用的 OpenFile(name, O_RDONLY, 0)
    									// filename 不存在就就报错
	if err!=nil{

		fmt.Println("出错啦")
	}
	err1 := errors.New("错误")
	fmt.Println("出错啦",err1)
    fmt.Println(string(f))

2.每次读多少字节

f,err:=os.Open("./log.text")  // OpenFile(name, O_RDONLY, 0) 不存在就报错
    if err !=nil{
        fmt.Println("出错啦",err)
    }
    b:=make([]byte,3)
        for {
            _, err1 := f.Read(b)
            if err1 == io.EOF {
                fmt.Println(string(b))
                break
            } else if err1 != nil {
                fmt.Println("粗错啦")
                break
            } else {
                fmt.Println(string(b))
            }
        }

3.按行读

f,err:=os.Open("./log.text")
	if err !=nil{
			fmt.Println("出错啦",err)
		}
	s:=bufio.NewScanner(f)
	for s.Scan(){
		fmt.Println(s.Text())
	}

4.创建(存在就清空)

fileobj, _ := os.Create("./creat.test")  //OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
writeString, _ := fileobj.WriteString("哈哈哈\n")
fmt.Println(writeString)

5.append追加

f,_:=os.OpenFile("./log.text",os.O_CREATE|os.O_APPEND|os.O_RDWR,0666)
	for i:=0;i<10;i++{
		f.WriteString(fmt.Sprintf("哈哈哈%d\n",i))
	}