Read the File record in Node.js

In the previous chapters, you found that you used a lot of require syntax ("fs"). So what is the syntax to do? This is the syntax to declare fs Module to deploy File I / O operations in Node.js. The syntax is as follows:

 var fs = require ( "fs" ) 

The Concept of Sync vs. Asynchronous in Node.js

Each method in fs Module has synchronous forms and asynchronous forms. Asynchronous methods take a final parameter as an end callback function and get the first parameter as a callback function to handle the error. Using asynchronous methods is better than synchronous methods, because asynchronous methods never lock the program runtime while the sync method does.

For example

To illustrate the I / O operation in Node.js, first create input.txt with the content:

 QTM is a Web page that contains all the scripts 
 Welcome to the world !!!!!! 

Create main.js. As mentioned above, each method of fs Module has two forms that are synchronous and asynchronous. To read the data, I use the asynchronous form readFile () method and readFileSync () of the synchronized form to read the data. These two methods take the first parameter as the file name to read the data from.

 var fs = require ( "fs" ); // The file method is not available . readFile ( 'input.txt' , function ( err , data ) { if ( err ) { return console . error ( err ); } console . log ( "The file is not installed:" + data . toString ()) ; }); // Method of file file to install var data = fs . readFileSync ( 'input.txt' ); console . log ( "File method:" + data . toString ()); console . log ( "Ket process" ); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 File sharing method: QTM is a Web page that contains all files 
 Welcome to the world !!!!!! 

 Let's get married 
 The file method does not work: QTM is a Web page that contains all files 
 Welcome to the world !!!!!! 

In the next section, I will detail the common file I / O activities:

Open a File in Node.js

Syntax

To open a file in asynchronous mode, you use the open () method with the syntax:

 fs . open ( path , flags [, mode ], callback ) 

Parameters

path - This is a string that represents the file name as well as the path to the file.

flags - Shows the behavior of the file opened. All values ​​may be presented in the table below.

mode - Set the mode for the file, these modes are set only when the file has been created. The default value is 0666, ie readable and writeable.

callback - The callback function takes two parameters, for example (err, fd).

Flags are used for Read / Write files in Node.js

Flag Description Open the file to read. Exception occurs if the file does not exist. r + Open file to read and write. Exception occurs if the file does not exist. rs Open the file to read in synchronous mode. rs + Open file to read and write, tell OS to open it in synchronous mode. w Open the file to record. If the file does not exist, it will create a new file. wx Like 'w' but this operation fails if the file does not exist (ie it does not create a new file). w + Open the file to read and write. If the file does not exist, it will create a new file. wx + Like 'w +' but this operation fails if the file does not exist a Open the file to append. The file will be created if it does not exist. ax Same 'a' but this operation fails if the file does not exist. a + Open the file to read and append. The file will be created if it does not exist. ax + Same as 'a +' but this operation fails if the file does not exist.

For example

The following example illustrates how to open a file to read and write. First, create main.js with the following content. The content of the file is quite similar to the above example, you pay attention to the flag used here.

 var fs = require ( "fs" ); // File download by using the console . log ( "Chuan bi File download!" ); fs . open ( 'input.txt' , 'r +' , function ( err , fd ) { if ( err ) { return console . error ( err ); } console . log ( "File is a curve!" ); }); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 Chuan bi file File download! 
 File is a curvy! 

Get the File information in Node.js

Syntax

To get information about a file in Node.js, you use the stat () method of fs Module with the syntax:

 fs . stat ( path , callback ) 

Details about parameters

path - This is a string that represents the file name as well as the path to the file.

callback - A callback function that takes two parameters (err, stats), where stats is an object of fs.Stats printed as in the following example.

In addition to the important properties printed as in the following example, the fs.Stats class also has some useful methods that can be used to check file types. That is:

Method Descriptionstats.isFile () Returns true if it is a file stats.isDirectory () Returns true if it is a stats.isBlockDevice directory () Returns true if it is a Block Device. stats.isCharacterDevice () Returns true if it is a Character Device. stats.isSymbolicLink () Returns true if it is a Symbolic Link. stats.isFIFO () Returns true if it is a FIFO type. stats.isSocket () Returns true if it's a Socket type.

For example

Here is an example to illustrate how to get information about a file. Create main.js and use the stat () method of fs Module shown above:

 var fs = require ( "fs" ); console . log ( "How to save file information!" ); fs . stat ( 'input.txt' , function ( err , stats ) { if ( err ) { return console . error ( err ); } console . log ( stats ); console . log ( "Lay information File thanh cong!" ) ; // Check the file console . Log ( "isFile?" + Stats . IsFile ()); console . Log ( "isDirectory?" + Stats . IsDirectory ()); }); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 You will be able to file information directly! 
 {dev: 1792, 
 mode: 33188, mode: 33188, 
 nlink: 1, nlink: 1, 
 uid: 48, uid: 48, 
 gid: 48, gid: 48, 
 rdev: 0, rdev: 0, 
 blksize: 4096, blksize: 4096, 
 ino: 4318127, ino: 4318127, 
 size: 97, size: 97, 
 blocks: 8, blocks: 8, 
 atime: Sun Mar 22 2015 13:40:00 GMT-0500 (CDT), atime: Sun Mar 22 2015 13:40:00 GMT-0500 (CDT), 
 mtime: Sun Mar 22 2015 13:40:57 GMT-0500 (CDT), mtime: Sun Mar 22 2015 13:40:57 GMT-0500 (CDT), 
 ctime: Sun Mar 22 2015 13:40:57 GMT-0500 (CDT) } ctime: Sun Mar 22 2015 13:40:57 GMT-0500 (CDT)} 
 Lay information File bar! 
 isFile? true 
 isDirectory? false 

Write data to File in Node.js

Syntax

To write data to File in Node.js, you can use the writeFile () method of fs Module as follows:

 fs . writeFile ( filename , data [, options ], callback ) 

This method will override if the file already exists.

Details about parameters

path - This is a string that represents the file name as well as the path to the file.

data - Data as String or Buffer to write to File.

options - This parameter is an object that holds {encoding, mode, flag}. By default, encoding is utf8, mode is 0666 and flag is 'w'

callback - The callback function takes one parameter err and is used to return an error if any error occurs in the write operation.

For example

The following example illustrates how to write data to a file. Creating main.js has the following content:

 var fs = require ( "fs" ); console . log ( "Earlier file recording" ); fs . writeFile ( ' input.txt ' , 'Hoc Node.js has a QTM board!' , function ( err ) { if ( err ) { return console . error ( err ); } console . log ( "Write the file to the file curved! " ); console . log ( " Doc du lieu king "recorded ); fs . readFile ( 'input.txt' , function ( err , data ) { if ( err ) { return console . error ( err ); } console . ( log file) "No data :" + data . toString ()); }); }); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 The file is written into the file 
 Write down the file in the bar file! 
 Doc du lieu king recorded 
 The file method is not available: Learning Node.js with QTM board! 

Read data from File in Node.js

Syntax

To read data from a File, you use the read () method with the following syntax:

 fs . read ( fd , buffer , offset , length , position , callback ) 

This method will use the parameter fd (short for File Descriptor) to read the file. If you want to read the file using the file name directly, you should use another method.

Details about parameters

fd - An abbreviation of file descriptor returned by the method fs.open ().

buffer - This is the Buffer, where the data is written.

offset - This is the offset in the Buffer so that data begins to record from that location.

length - An integer specifying the number of bytes to read.

position - An integer specifying where to start reading from within the file. If the location is null, the data will be read from the current location of the file.

callback - A callback function that takes three parameters, shaped (err, bytesRead, buffer).

For example

Create main.js with the following content:

 var fs = require ( "fs" ); var buf = new Buffer ( 1024 ); console . log ( "Chuan is file-oriented" ); fs . open ( 'input.txt' , 'r +' , function ( err , fd ) { if ( err ) { return console . error ( err ); } console . log ( "File of the curve!" ); console . log ( "You are required to use the mo file" ) fs . Read ( fd , buf , 0 , buf . Length , 0 , function ( err , bytes ) { if ( err ) { console . Log ( err ); } console . log ( bytes + "bytes read" ); // In so luong byte da doc. if ( bytes > 0 ) { console . log ( buf . slice ( 0 , bytes ). toString ()); } }); }); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 Chuan is a file 
 File is a curvy! 
 I want to study the file of mo 
 97 bytes read 
 QTM is a Web page that contains all the scripts 
 Welcome to the world !!!!!! 

Close File in Node.js

Syntax

To close a file after opening, you use the close () method with the syntax:

 fs . close ( fd , callback ) 

Details about parameters

fd - An abbreviation of file descriptor returned by the method fs.open ().

callback - The callback function takes a parameter to handle the case if there is an exception.

For example

Create main.js with content:

 var fs = require ( "fs" ); var buf = new Buffer ( 1024 ); console . log ( "Chuan is file-oriented" ); fs . open ( 'input.txt' , 'r +' , function ( err , fd ) { if ( err ) { return console . error ( err ); } console . log ( "File of the curve!" ); console . log ( "You are required to use the mo file" ) fs . Read ( fd , buf , 0 , buf . Length , 0 , function ( err , bytes ) { if ( err ) { console . Log ( err ); } // In so luong byte da doc. If ( bytes > 0 ) { console . Log ( buf . Slice ( 0 , bytes ). ToString ()); } // A king file. Fs . Close ( fd , function ( err ) { if ( err ) { console . log ( err ); } console . log ( "File is in the middle of the file." ); }); }); }); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 Chuan is a file 
 File is a curvy! 
 I want to study the file of mo 
 QTM is a Web page that contains all the scripts 
 Welcome to the world !!!!!! 

 The file is scrolled. 

Truncate a File in Node.js

Syntax

To truncate an open file, you use the ftruncate () method with the syntax:

 fs . ftruncate ( fd , len , callback ) 

Details about parameters

fd - An abbreviation of file descriptor returned by the method fs.open ().

len - The length of the file after it has been truncate.

callback - The callback function takes a parameter to handle the case if there is an exception.

For example

Create main.js with the following content:

 var fs = require ( "fs" ); var buf = new Buffer ( 1024 ); console . log ( "Chuan is file-oriented" ); fs . open ( 'input.txt' , 'r +' , function ( err , fd ) { if ( err ) { return console . error ( err ); } console . log ( "File of the curve!" ); console . log ( "Chuan bi truncate file" ) // Truncate has a file. Fs . Ftruncate ( fd , 10 , function ( err ) { if ( err ) { console . Log ( err ); } console . Log ( "File console . log ( "Chuan bi tu tu tu tu" ); fs . read ( fd , buf , 0 , buf . length , 0 , function ( err , bytes ) { if ( err ) { console . log ( err ); } // In so luong byte da doc. if ( bytes > 0 ) { console . log ( buf . slice ( 0 , bytes ). toString ()); } // Dong File king mo . fs . close ( fd , function ( err ) { if ( err ) { console . log ( err ); } console . log ( "The file is in the curvature." ); }); }); }) ) ; 

Run main.js to see the result:

 $ node main . js 

Check the result:

 Chuan is a file 
 File is a curvy! 
 You can truncate the file 
 The file must be truncate the curved bar. 
 Please read the file 
 VietNamVo 
 The file is scrolled. 

Delete File in Node.js

Syntax

To delete a file in Node.js, you use the unlink () method with the syntax:

 fs . unlink ( path , callback ) 

Details about parameters

path - The file name or path name that points to the file.

callback - The callback function takes a parameter to handle the case if there is an exception.

For example

Create main.js with the following content:

 var fs = require ( "fs" ); console . log ( "Chuan is using a file" ); fs . unlink ( 'input.txt' , function ( err ) { if ( err ) { return console . error ( err ); } console . log ( "Delete File bar cong!" ); }); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 Chuan is a file 
 Rub File bar! 

Create a directory in Node.js

Syntax

To create a directory in Node.js, you use the mkdir () method with the syntax:

 fs . mkdir ( path [, mode ], callback ) 

Details about parameters

path - This is the directory name that includes the path to the directory.

mode - Mode that determines permissions when accessing folders. The default value is 0777.

callback - The callback function takes a parameter to handle the case if there is an exception.

For example

Create main.js with the following content:

 var fs = require ( "fs" ); console . log ( "Chuan is creating a folder / tmp / test" ); fs . mkdir ( '/ tmp / test' , function ( err ) { if ( err ) { return console . error ( err ); } console . log ( "How to create a directory!" ); }); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 Chuan is creating a folder / tmp / test 
 The folder has a curved bar! 

Read the directory in Node.js

Syntax

To read the directory in Node.js, you use the readdir () method with the syntax:

 fs . readdir ( path , callback ) 

Details about parameters

path - This is the directory name that includes the path to the directory.

callback - The callback function takes two parameters, form (err, files) in which files are an array containing file names in the directory.

For example

Create main.js with the following content:

 var fs = require ( "fs" ); console . log ( "Please read the file / tmp" ); fs . readdir ( "/ tmp /" , function ( err , files ) { if ( err ) { return console . error ( err ); } files . forEach ( function ( file ) { console . log ( file ); }); }) ; 

Run main.js to see the result:

 $ node main . js 

Check the result:

 Please read the news file / tmp 
 ccmzx99o.out 
 ccyCSbkF.out 
 employee.ser 
 hsperfdata_apache 
 kiểm TRA 
 test.txt 

Delete the directory in Node.js

Syntax

To delete a directory in Node.js, you use the rmdir () method with the syntax:

 fs . rmdir ( path , callback ) 

Details about parameters

path - This is the directory name that includes the path to the directory.

callback - The callback function takes a parameter to handle the case if there is an exception.

For example

Create main.js with the following content:

 var fs = require ( "fs" ); console . log ( "Chuan bi rub the folder / tmp / test" ); fs . rmdir ( "/ tmp / test" , function ( err ) { if ( err ) { return console . error ( err ); } console . log ( "Chuan bi doc the file / tmp" ); fs . readdir ( "/ tmp /" , function ( err , files ) { if ( err ) { return console . error ( err ); } files . forEach ( function ( file ) { console . log ( file ); }); }; } ); 

Run main.js to see the result:

 $ node main . js 

Check the result:

 Please read the news file / tmp 
 ccmzx99o.out 
 ccyCSbkF.out 
 employee.ser 
 hsperfdata_apache 
 test.txt 

According to Tutorialspoint

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