Node.js - File System

Node.js - File System

Using simple wrappers around standard POSIX functions Node implements File I / O. You may import the Node File System (fs) module using the following syntax.

var fs = require("fs")

Synchronous vs Asynchronous

In the fs module each method has both synchronous and asynchronous forms. Asynchronous methods take the final parameter as the callback completion function and the first callback function parameter as error. Rather than using a synchronous method, it is better to use an asynchronous method, since the former never blocks a program during its execution, while the latter does.

Creates a text file named input.txt with the content –

Keep Training and keep Learning

Until you get it Right !!!!!

var fs = require("fs");
// Asynchronous read
fs.readFile('input.txt', function (err, data) {
if (err) {
return console.error(err);
}
console.log("Asynchronous read: " + data.toString());
});
// Synchronous read
var data = fs.readFileSync('input.txt');
console.log("Synchronous read: " + data.toString());
console.log("Program Ended");

Run main.js now to see the result –

$ node main.js

The following sections in this chapter include a collection of strong examples of major methods for I / O files.

Open a File

The method to open a file in asynchronous mode is syntaxed below –

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

Parameter Value

Here is the description of the parameters to be used –

The read / write flags are-

Let's create a js file named main.js with the following code to open a file named input.txt.

var fs = require("fs");
// Asynchronous - Opening File
console.log("Going to open file!");
fs.open('input.txt', 'r+', function(err, fd) {
if (err) {
return console.error(err);
}
console.log("File opened successfully!");     
});

Run main.js now to see the result –

$ node main.js

Get File Information

Following is the method syntax for obtaining information on a file –

fs.stat(path, callback)

Parameter Value

The description of the parameters is used here-

Let's create a Js file named main.js with the code –

var fs = require("fs");
console.log("Going to get file info!");
fs.stat('input.txt', function (err, stats) {
if (err) {
return console.error(err);
}
console.log(stats);
console.log("Got file info successfully!");
// Check file type
console.log("isFile ? " + stats.isFile());
console.log("isDirectory ? " + stats.isDirectory());    
});

Run main.js now to see the result –

$ node main.js

Writing a File

The syntax of one of the methods to write to a file follows –

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

If the file already exists this method will overwrite the file. If you want to write to an existing file then use another available method.

Parameter Value

Let's create a file called main.js which has the following code –

var fs = require("fs");
console.log("Going to write into existing file");
fs.writeFile('input.txt', Keep Learning Keep Training!', function(err) {
if (err) {
return console.error(err);
}
console.log("Data written successfully!");
console.log("Let's read newly written data");
fs.readFile('input.txt', function (err, data) {
if (err) {
return console.error(err);
}
console.log("Asynchronous read: " + data.toString());
});
});

Run main.js now to see the result –

$ node main.js

Reading a File

The syntax of one of the methods to be read from a file follows –

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

This method is used to read the file using file descriptor. If you want to read the file using the file name directly, then you should use another available method.

Parameter Value

Let's create a Js file named main.js with the code –

var fs = require("fs");
var buf = new Buffer(1024);
console.log("Going to open an existing file");
fs.open('input.txt', 'r+', function(err, fd) {
if (err) {
return console.error(err);
}
console.log("File opened successfully!");
console.log("Going to read the file");
fs.read(fd, buf, 0, buf.length, 0, function(err, bytes){
if (err){
console.log(err);
}
console.log(bytes + " bytes read");
// Print only read bytes to avoid junk.
if(bytes > 0){
console.log(buf.slice(0, bytes).toString());
}
});
});

Run main.js now to see the result –

$ node main.js

Closing a File

The syntax follows to close an opened file –

fs.close(fd, callback)

Parameter Value

The description of the parameters is used here-

Let's create a file called main.js which has the following code –

var fs = require("fs");
var buf = new Buffer(1024);
console.log("Going to open an existing file");
fs.open('input.txt', 'r+', function(err, fd) {
if (err) {
return console.error(err);
}
console.log("File opened successfully!");
console.log("Going to read the file");

fs.read(fd, buf, 0, buf.length, 0, function(err, bytes) {
if (err) {
console.log(err);
}

// Print only read bytes to avoid junk.
if(bytes > 0) {
console.log(buf.slice(0, bytes).toString());
}

// Close the opened file.
fs.close(fd, function(err) {
if (err) {
console.log(err);
} 
console.log("File closed successfully.");
});
});
});

Run main.js now to see the result –

$ node main.js

Truncate a File

The method to truncate an opened file is syntaxed below-

fs.ftruncate(fd, len, callback)

Parameter Value

The description of the parameters is used here-

Let's create a file called main.js which has the following code –

var fs = require("fs");
var buf = new Buffer(1024);
console.log("Going to open an existing file");
fs.open('input.txt', 'r+', function(err, fd) {
if (err) {
return console.error(err);
}
console.log("File opened successfully!");
console.log("Going to truncate the file after 10 bytes");

// Truncate the opened file.
fs.ftruncate(fd, 10, function(err) {
if (err) {
console.log(err);
} 
console.log("File truncated successfully.");
console.log("Going to read the same file"); 
fs.read(fd, buf, 0, buf.length, 0, function(err, bytes){
if (err) {
console.log(err);
}
// Print only read bytes to avoid junk.
if(bytes > 0) {
console.log(buf.slice(0, bytes).toString());
}
// Close the opened file.
fs.close(fd, function(err) {
if (err) {
console.log(err);
} 
console.log("File closed successfully.");
});
});
});
});

Run main.js now to see the result –

$ node main.js

Delete a File

Following is a syntax of the file deletion method –

fs.unlink(path, callback)

Parameter Value

The description of the parameters is used here-

Let's create a file called main.js which has the following code –

var fs = require("fs");
console.log("Going to delete an existing file");
fs.unlink('input.txt', function(err) {
if (err) {
return console.error(err);
}
console.log("File deleted successfully!");
});

Run main.js now to see the result –

$ node main.js

Create a Directory

The method to create a directory is syntaxed below –

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

Parameter Value

The description of the parameters is used here-

Let's create a file called main.js which has the following code –

var fs = require("fs");
console.log("Going to create directory /tmp/test");
fs.mkdir('/tmp/test',function(err) {
if (err) {
return console.error(err);
}
console.log("Directory created successfully!");
});

Run main.js now to see the result –

$ node main.js

Read a Directory

The syntax of the method for reading a directory follows –

fs.readdir(path, callback)

Parameter Value

The description of the parameters is used here-

Let's create a file called main.js which has the following code –

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

Run main.js now to see the result –

$ node main.js

Remove a Directory

Following is the method syntax for deleting a directory –

fs.rmdir(path, callback)

Parameter Value

The description of the parameters is used here-

Let's create a file called main.js which has the following code –

var fs = require("fs");
console.log("Going to delete directory /tmp/test");
fs.rmdir("/tmp/test",function(err) {
if (err) {
return console.error(err);
}
console.log("Going to read directory /tmp");
fs.readdir("/tmp/",function(err, files) {
if (err) {
return console.error(err);
}
files.forEach( function (file) {
console.log( file );
});
});
});

Run main.js now to see the result –

$ node main.js