Two global variables__ Dirname and__ Further introduction to common functions of filename and FS modules

The authorities provided it to us __dirname and __filename These two variables , Note that their values are strings .

__dirname： On behalf of the current js The path to the directory where the file is located ( Absolute path )

__filename:  On behalf of the current js Path to file ( Absolute path )

Show me ： Create a new one js file , Print these two variables .

console.log(__dirname);
console.log(__filename);

Terminal results ：

fs Module common functions

Read the file fs.readFile(path,(err,data)=>{})

Parameter description ：

path: The path to read the file ( It could be an absolute path , Can be a relative path );

err: The information returned from reading failure ;

data： Read the binary type data returned successfully , We can go through toString() Method to string .

Code demonstration ：

First create one under the same directory test.txt, Text file with test text , We'll use readFile() Read .

const fs=require("fs")

fs.readFile("./test.txt",(err,data)=>{
    console.log(err,data.toString());
})

The terminal prints the results ：

Read file successful err return null,data Return the contents of the file , Because in the toString（） Convert to string , We can see the test text , If not, binary data will be printed .

write file fs.writeFile(path,data,callback(err))

Parameter description ：

path: For the path we want to write to the file ;

data: The data to be written ;

callback(err): Callback function , When writing to a file fails ,err Return error message .

Note that when we write a file , If the file already exists in the write path , Then our new writing will overwrite the original , If not, create the file .

Code demonstration ：

When there is no such file

fs.writeFile("./newtxt.txt"," newly build txt",(err)=>{
    // If the failure returns an error message 
    console.log(err);
})

  function js file , At this time, the folder has been successfully created newtxt.txt

 

  When the folder already exists

fs.writeFile("./newtxt.txt"," I established it for the second time txt",(err)=>{
    // If the failure returns an error message 
    console.log(err);
})

Run code , You can see that the content of the text has changed

 

  Delete file fs.unlink(path,callback(err))

Parameter description ：

path: Delete the path of the file , For the string

callback(err): Callback function ,err Error message when deleting file , success err by null

Code demonstration ：

fs.unlink("./newtxt.txt",(err)=>{
    console.log(err);
})

  Running results ：

You can see the file written above newtxt.txt It has been deleted . 

 

Additional content   fs.appendFile(path,content,callback(err))

Parameter description ：

path: The path of the append file , In the form of string ;

content: Additional content

callback(err)： Callback function ,err Error message returned for append failure , Append succeeded err by null

Code demonstration ：

fs.appendFile("./test.txt"," I am a new content ",(err)=>{
    console.log(err);
})

Running results ： 

 

  If path The path does not exist in the folder , Then it will automatically create this file for us .

for example ：

 

Create directory fs.mkdir(path,callback(err))

Parameter description ：

path: The path to create the directory , The format is also a string ;

callback: Callback function , Parameters err Error message returned for creation failure ;

Code demonstration ：

fs.mkdir(__dirname+"/newfile",(err)=>{
    //dirname by node Path to folder 
    console.log(err);
})

  Running results ：

 

Move / Rename a file or directory fs.rename(oldpath,newpath,callback(err))

Parameter description ：

oldpath, Original catalogue / The full path and name of the file ;

newpath, New catalog / The full path and name of the file ; If the new path is the same as the original path , Only the file name is different , It's about renaming

callback(err), Operation completion callback function ;err Operation failed object

Moving files has a bug: The new path and the old path must be the same root disk

Code demonstration ：

// rename 
let oldpath=__dirname+"/test.txt"
let newpath=__dirname+"/newtest.txt"
fs.rename(oldpath,newpath,(err)=>{
    console.log(" Rename successful ");
})

// Move 
let oldpath1=__dirname+"/tes.txt"
let newpath1=__dirname+"/newfile/tes.txt"
fs.rename(oldpath1,newpath1,(err)=>{
    console.log(" Mobile success ");
})

Running results ：

 

  Copy files fs.copyFile(oldpath, newpath, callback(err) ）

Parameter description ：

oldpath, The full path of the original file ;

newpath, The full path of the new file ;

callback(err), Operation completion callback function ;err Operation failed object

Code demonstration ：

let oldpath=__dirname+"/newtest.txt"
let newpath=__dirname+"/newfile/newtest.txt"
fs.copyFile(oldpath,newpath,(err)=>{
    console.log(" Success copy ");
})

  Running results ： The contents of the two files are the same