I. Basic API for file operation

func main() {
    //Absolute path
    fileInfo , err := os.Stat("E:/a.txt")
    fileInfo , err = os.Stat("E:/")
    if err !=nil {
        fmt.Println("err:" , err.Error())
    } else {
        fmt.Printf("%T \n" , fileInfo)
        fmt.Printf("%v \n" , fileInfo)
        //file name
        fmt.Println(fileInfo.Name())
        //Is it a directory
        fmt.Println(fileInfo.IsDir())
        //File size size
        fmt.Println(fileInfo.Size())
        //mode Jurisdiction
        fmt.Println(fileInfo.Mode())
        //File last modified
        fmt.Println(fileInfo.ModTime())
    }
}

File path:

• 1. Absolute path: absolute
• 2. Relative path: relative is equivalent to the current project (. Current directory.. upper level)

(1) judge whether it is the absolute path filepath.IsAbs()
(2) get the relative path filepath.Rel()
(3) get the absolute path filepath.Abs()
(4) path.Join()

File operation:
1. Create the folder. If the folder exists, the creation fails

• os.MKdir()
• os.MKdirAll()

2. Create file: if the file exists, it will be overwritten

• os.Create()-->*file

3. Open file:

• os.Open(filename)
• os.OpenFile(filename,mode,perm)

4. Close file:

• file.Close()

5. delete:

• os.Remove()
• os.RemoveAll()

package main

import (
    "os"
    "fmt"
)

func main() {
    /*
    File operation:
        1.Create folder. If the folder exists, the creation fails
            os.MKdir()
            os.MKdirAll()

        2.Create file: overwrite if file exists
            os.Create()-->*file

        3.Open file:
            os.Open(filename)
            os.OpenFile(filename,mode,perm)
        4.Close file:
            file.Close()
        5.Delete:
            os.Remove()
            os.RemoveAll()
     */
    //     1,Create directory
    fileName1 := "./test1"
    err := os.Mkdir(fileName1, os.ModePerm)
    if err != nil {
        fmt.Println("err:", err.Error())
    } else {
        fmt.Printf("%s Directory created successfully!\n", fileName1)
    }

    fileName2 := "./test2/abc/xyz"
    err = os.MkdirAll(fileName2, os.ModePerm)
    if err != nil {
        fmt.Println("err:", err.Error())
    } else {
        fmt.Printf("%s Directory created successfully!\n", fileName2)
    }

    //2,create a file.If the file already exists, the file is overwritten
    fileName3 := "./test1/abc.txt"
    file1, err := os.Create(fileName3)
    if err != nil {
        fmt.Println("err:", err.Error())
    } else {
        fmt.Printf("%s Created successfully!%v \n", fileName3, file1)
    }

    //    3,Open file
    file2, err := os.Open(fileName3)
    if err != nil {
        fmt.Println("err:", err.Error())
    } else {
        fmt.Printf("%s Open successfully!%v \n", fileName3, file2)
    }

    /*
    First parameter: file name
    Second parameter: how to open the file
        O_RDONLY: Read only mode
        O_WRONLY: Write only mode
        O_RDWR: Read write mode
        O_APPEND: Append mode
        O_CREATE: create a new file if none exists
    The third parameter: permission of file: the file does not exist. You need to specify permission
     */
    fileName4 := "./test1/abc2.txt"
    file4, err := os.OpenFile(fileName4, os.O_RDWR|os.O_CREATE, os.ModePerm)
    if err != nil {
        fmt.Println("err:", err.Error())
    } else {
        fmt.Printf("%s Open successfully!%v \n", fileName4, file4)
    }

    //4,Close the file and disconnect the program from the file
    file4.Close()

    //    5,Delete files and directories
    fileName5 := "./test1"
    err = os.Remove(fileName5)
    if err != nil {
        fmt.Println(err)
    } else {
        fmt.Printf("%s Delete successfully!" , fileName5)
    }

    err = os.RemoveAll(fileName5)
    if err != nil {
        fmt.Println(err)
    } else {
        fmt.Printf("%s Delete successfully!" , fileName5)
    }
}

File read / write

/**
2.Read file. Read ([] byte) -- > N, err starts to read data from the file and stores it in the byte slice. The return value n is the actual amount of data read this time. If read to the end of the file, n is 0,err is EOF: end of file.
 */
func readFile(fileName string){
    file2,err:=os.OpenFile(fileName, os.O_RDWR|os.O_CREATE, os.ModePerm)
    if err!=nil{
        fmt.Println(file2);
    }else {
        bs:=make([]byte,8,1024*8);
        n:= -1;
        str:="";
        for{
            n,err=file2.Read(bs);
            fmt.Printf("n:%v \n",n)
            if n==0||err==io.EOF{
                fmt.Println("read file end")
                break;
            }
            str= strings.Join([]string{str,string(bs[:n])},"")
        }
        fmt.Println(str)
    }
    //3,Close file
    file2.Close()
}
func writeFile(fileName string){
    str:="I Love China I love China";
    bs:=[]byte(str);
    file2,err:=os.OpenFile(fileName, os.O_RDWR|os.O_CREATE, os.ModePerm)
    if err!=nil{
        fmt.Println(file2);
    }else {
        file2.Write(bs);
    }
    file2.Close();
}

II. ioutil package

/*
ioutil bag:
ReadFile() / / read all the data in the file and return the byte array read
WriteFile() / / writes data to the specified file. If the file does not exist, create the file and empty the file before writing the data
ReadDir() / / read the sub contents of a directory: sub files and sub directories, but only one layer
TempDir() / / in the current directory, create a temporary folder prefixed with the specified string and return the folder path
TempFile() / / in the current directory, create a file prefixed with the specified string, open the file in read-write mode, and return the os.File pointer object
*/

package main

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

func main() {
    /*
    ioutil Bag:
        ReadFile()   //Read all the data in the file and return the byte array read
        WriteFile()  //Write data to the specified file. If the file does not exist, create the file and empty the file before writing the data
        ReadDir()    //Read the sub contents of a directory: sub files and sub directories, but only one layer
        TempDir()   //In the current directory, create a temporary folder prefixed with the specified string and return the folder path
        TempFile()   //In the current directory, create a file prefixed with the specified string, open the file in read-write mode, and return the os.File pointer object
     */
    //1,ReadFile()   //Read all the data in the file and return the byte array read
    fileName1 := "./files/blockchain.txt"
    data, err := ioutil.ReadFile(fileName1)
    if err != nil {
        fmt.Println("File open exception", err.Error())
    } else {
        fmt.Println(string(data))
    }

    //2,WriteFile()  //Write data to the specified file. If the file does not exist, create the file and empty the file before writing the data
    fileName2 := "./files/xyz.txt"
    s1 := "Steven With your school district block chain"
    err = ioutil.WriteFile(fileName2, []byte(s1), 0777)
    if err != nil {
        fmt.Println("Write file exception", err.Error())
    } else {
        fmt.Println("File write OK!")
    }

    //3,File copy
    err = ioutil.WriteFile(fileName2 , data , os.ModePerm)
    if err != nil {
        fmt.Println("File copy exception", err.Error())
    } else {
        fmt.Println("File copied successfully!")
    }

    //4,ReadDir()    //Read the sub contents of a directory: sub files and sub directories, but only one layer
    dirName := "./"
    fileInfos , err := ioutil.ReadDir(dirName)
    if err != nil {
        fmt.Println("Directory traversal exception", err.Error())
    } else {
        for i , v := range fileInfos {
            fmt.Println(i , v.Name() , v.IsDir() , v.Size() , v.ModTime())
        }
    }

    //5,TempDir()   //In the current directory, create a temporary folder prefixed with the specified string and return the folder path
    filename , err := ioutil.TempDir("./" , "temp")
    if err != nil {
        fmt.Println("Failed to create directory" , err.Error())
    } else {
        fmt.Println(filename)
    }

    //6,TempFile()   //In the current directory, create a file prefixed with the specified string, open the file in read-write mode, and return os.File Pointer object
    file1 , err := ioutil.TempFile(filename , "temp")
    if err != nil {
        fmt.Println("Failed to create file" , err.Error())
    } else {
        file1.WriteString("Write contents:" + file1.Name())
    }
    file1.Close()
}