Node.js foundation course

Chapter 05 - File System

In Order to use this module

var fs = require('fs');

Lesson 01-1 - Reading Contents of a directory Asynchronously

fs.readdir(path[, options], callback)

• path <String> | <Buffer>
  
• options <String> | <Object>
  
• encoding <String> default = 'utf8'`
  
• callback <Function>
  

The callback gets two arguments (err, files) where files is an array of the names of the files

https://nodejs.org/api/fs.html#fs_fs_readdir_path_options_callback

Lesson 01-2 - Reading Contents of a directory Synchronously

fs.readdirSync(path[, options])

• path <String> | <Buffer>
  
• options <String> | <Object>
  
• encoding <String> default = 'utf8'`
  

[https://nodejs.org/api/fs.html#fs_fs_readdirsync_path_options] (https://nodejs.org/api/fs.html#fs_fs_readdirsync_path_options)

Lesson 02-1 - Reading Contents of a file Asynchronusly

fs.readFile(file[, options], callback)

• file <String> | <Buffer> | <Integer> filename or file descriptor
  
• options <Object> | <String>
  
• encoding <String> | <Null> default = null
  
• flag <String> default = 'r'
  
• callback <Function>
  

Example

fs.readFile('/etc/passwd', (err, data) => {
    if (err) throw err;
    console.log(data);
});

[https://nodejs.org/api/fs.html#fs_fs_readfile_file_options_callback] (https://nodejs.org/api/fs.html#fs_fs_readfile_file_options_callback)

Lesson 02-2 - Reading Contents of a file Synchronusly

fs.readFileSync(file[, options])

• file <String> | <Buffer> | <Integer> filename or file descriptor
  
• options <Object> | <String>
  
• encoding <String> | <Null> default = null
  
• flag <String> default = 'r'
  

Synchronous version of fs.readFile. Returns the contents of the file If the encoding option is specified then this function returns a string. Otherwise it returns a buffer.

[https://nodejs.org/api/fs.html#fs_fs_readfilesync_file_options] (https://nodejs.org/api/fs.html#fs_fs_readfilesync_file_options)

Lesson 03-1 - Writing Contents to a file Synchronusly

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

• file <String> | <Buffer> | <Integer> filename or file descriptor
  
• data <String> | <Buffer>
  
• options <Object> | <String>
  
• encoding <String> | <Null> default = 'utf8'
  
• mode <Integer> default = 0o666
  
• flag <String> default = 'w'
  
• callback <Function>
  

Asynchronously writes data to a file, replacing the file if it already exists. data can be a string or a buffer.

The encoding option is ignored if data is a buffer. It defaults to 'utf8'

fs.writeFile('message.txt', 'Hello Node.js', (err) => {
    if (err) throw err;
        console.log('It\'s saved!');
});

If options is a string, then it specifies the encoding. Example: fs.writeFile('message.txt', 'Hello Node.js', 'utf8', callback);

[https://nodejs.org/api/fs.html#fs_fs_writefile_file_data_options_callback] (https://nodejs.org/api/fs.html#fs_fs_writefile_file_data_options_callback)

Lesson 04-1 - Append data to a file Asynchronusly

fs.appendFile(file, data[, options], callback)

• file <String> | <Buffer> | <Number> filename or file descriptor
  
• data <String> | <Buffer>
  
• options <Object> | <String>
  
• encoding <String> | <Null> default = 'utf8'
  
• mode <Integer> default = 0o666
  
• flag <String> default = 'a'
  
• callback <Function>
  

Asynchronously append data to a file, creating the file if it does not yet exist. data can be a string or a buffer.

Example:

fs.appendFile('message.txt', 'data to append', (err) => {
  if (err) throw err;
  console.log('The "data to append" was appended to file!');
});

s.appendFile('message.txt', 'data to append', 'utf8', callback);

[https://nodejs.org/api/fs.html#fs_fs_appendfile_file_data_options_callback] (https://nodejs.org/api/fs.html#fs_fs_appendfile_file_data_options_callback)

Lesson 04-2 - Append data to a file Synchronusly

fs.appendFileSync(file, data[, options])

• file <String> | <Buffer> | <Number> filename or file descriptor
  
• data <String> | <Buffer>
  
• options <Object> | <String>
  
• encoding <String> | <Null> default = 'utf8'
  
• mode <Integer> default = 0o666
  
• flag <String> default = 'a'
  The synchronous version of fs.appendFile(). Returns undefined.

[https://nodejs.org/api/fs.html#fs_fs_appendfilesync_file_data_options] (https://nodejs.org/api/fs.html#fs_fs_appendfilesync_file_data_options)

Lesson 05-5 - Removing Files (Deleting) & Renaming

fs.unlinkSync(path)

• _path <String> | <Buffer>

[https://nodejs.org/api/fs.html#fs_fs_unlinksync_path] (https://nodejs.org/api/fs.html#fs_fs_unlinksync_path)

fs.rename(oldPath, newPath, callback)

• _oldPath <String> | <Buffer>
  
• _newPath <String> | <Buffer>
  
• _callback <Function>

[https://nodejs.org/api/fs.html#fs_fs_rename_oldpath_newpath_callback] (https://nodejs.org/api/fs.html#fs_fs_rename_oldpath_newpath_callback)

fs.renameSync(oldPath, newPath) oldPath | newPath |

https://nodejs.org/api/fs.html#fs_fs_renamesync_oldpath_newpath

---

stream

Writable streams

const myStream = getWritableStreamSomehow(); myStream.write('some data'); myStream.write('some more data'); myStream.end('done writing data');

https://nodejs.org/api/stream.html#stream_writable_streams

Readable streams

var stream = fs.createReadStream("./chat.log", "UTF-8"); stream.on("data", function(dataChunk){ process.stdout.write(chunks : ${dataChunk.length} |); data += dataChunk; //console.log(data); });