Commonly used class

Commonly used method

File Information Statistics

The fs.stat() and fs.statsync () methods are used to return a file or directory statistics object (type fs.stats).

const fs=require('fs');
fs.stat("./app.log",(err,stats)=>{
    if(err) throw err;
    console.log(stats);
  	console.log(stats.isFile())
})

/**** Displays the obtained information *******/
{
  dev: 1786362065.mode: 33206.nlink: 1.uid: 0.gid: 0.rdev: 0.blksize: 4096.ino: 1407374883658375.size: 12.blocks: 0.atimeMs: 1572344727794.7805.mtimeMs: 1572344727414.4744.ctimeMs: 1572344727414.4744.birthtimeMs: 1572344727413.4426.atime: 2019- 10- 29T10:25:27.795Z,
  mtime: 2019- 10- 29T10:25:27.414Z,
  ctime: 2019- 10- 29T10:25:27.414Z,
  birthtime: 2019- 10- 29T10:25:27.413Z
}

true
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The Fs. Stats object also provides the following methods to check the physical properties of a file:

const path='./htdocs';
fs.stat(path,(err,stats)=>{
    if(err){
        fs.mkdir(path);
    }else{
        fs.readdir(path,(err,list)=>{
            console.log(list)
        })
    }
})
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Read and write the entire contents of the file

For files with a small amount of data, you can read and write all the contents at one time.

Read file contents:

const path='./htdocs/index.html';
fs.readFile(path,(err,data)=>{
    if(err)throw err;
    console.log(data);
    console.log(data.toString())
})
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Write to a file:

const path='./htdocs/index.html';
var data="
 Hello world! 
"
fs.writeFile(path,data,(err)=>{
    if(err)throw err;
    console.log("Write data complete!");
})
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Note: If the file does not exist, the writeFile method automatically creates the file. If the target file exists, this method overwrites all the original content.

Append to file:

const path='./htdocs/index.html';
var data="
 I'm fine! 
"
fs.appendFile(path,data,(err)=>{
    if(err)throw err;
    console.log("Append data complete!");
})
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Note: If the target file does not exist, the appendFile method creates the file automatically; If the target file exists, the method appends new content to the original content.

Read and write parts of a file

To install some contents of a diarrhea File, perform the following steps: (1) Open a specified File and obtain the corresponding “File Descriptors”. (2) Read or write the contents of a specified part of the File. (3) Close the file for other processes to use.

Read part of the city:

const src='./htdocs/index.html';
fs.open(src,(err,fd)=>{
    if(err)throw err;
    const buf=Buffer.alloc(1024);
    fs.read(fd,buf,0.1024.0,(err,bytesRead,buffer)=>{
        if(err)throw err;
      	console.log("Actual number of moral bytes read: %d",bytesRead);
        console.log(buffer.toString('UTF-8'.0,bytesRead));
        fs.close(fd,(err)=>{
            if(err)throw err;
            console.log('File closed! ')}); })});/ / 45
//
 Hello world! 
 I'm fine! 
// File closed!
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Write part of the content:

const src='./htdocs/index.html';
fs.open(src,'w',(err,fd)=>{
    if(err)throw err;
    const buf=Buffer.from("< h3 > is really good! ");
    fs.write(fd,buf,0.'UTF-8',(err,bytesRead,string)=>{
        if(err)throw err;
        console.log("Write some content successfully!");
        console.log("Write bytes: %d, write content: %s",bytesRead,string)
        fs.close(fd,(err)=>{
            if(err)throw err;
            console.log('File closed! ')}); })});// Write some content successfully!
 
 
// File closed!
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Input stream object

The Stream.Readable object can emit the following events:

The Stream.Readable object can perform the following operations:

const fs=require('fs');

var read=fs.createReadStream('./htdocs/1.mp4');

var total=0;
read.on("data",(buf)=>{
    console.log("Data length: %d",buf.length);
    total+=buf.length;
})
read.on("end",(err)=>{
    if(err)throw err;
    console.log("File reading finished!");
    console.log("Total bytes read: %d",total);
})
read.on("close",(err)=>{
    if(err)throw err;
    console.log("Stream closed successfully!")})// Data length: 65536
// Data length: 65536
/ /...
// Data length: 65536
// Data length: 65536
// Data length: 65536
// Data length: 50848
// End of file reading!
// Read the total number of bytes: 117819040
// Stream closed successfully!
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Use the pipe

Pipe: a Pipe that can be used to automatically read all data from a Readable object and write it to a specified Writeable object.

const fs=require("fs");

const src="./htdocs/index.html";
const dest="./backup/index.html";

var read=fs.createReadStream(src);
var write=fs.createWriteStream(dest);

read.pipe(write);		// Use pipes for automatic reading and writing
reader.on("end",(err)=>{
	if(err)throw err;
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