Node.js fs.chmod() Method

The fs.chmod() method is used to change the permissions of a given path. These permissions can be specified using string constants or octal numbers that correspond to their respective file modes. Note: The Windows platform only supports the changing of the write permission. It also does not support the distinction between the permissions of user, group, or others. Syntax:

fs.chmod( path, mode, callback )

Parameters: This method accepts three parameters as mentioned above and described below:

• path: It is a string, Buffer or URL that denotes the path of the file of which the permission has to be changed.
• mode: It is string or octal integer constant that denotes the permission to be granted. The logical OR operator can be used to separate multiple permissions.
• callback: It is a function that would be called when the method is executed.
  • err: It is an error that would be thrown if the method fails.

Below examples illustrate the fs.chmod() method in Node.js: Example 1: This example shows the usage of octal integer constants to give the file permissions.

javascript

// Node.js program to demonstrate the
// fs.chmod() method

// Import the filesystem module
const fs = require('fs');

// Grant only read permission to user
console.log("Granting only read access to user");

fs.chmod("example.txt", 0o400, () => {
  console.log("\nReading the file contents");
  console.log(fs.readFileSync("example.txt", 'utf8'));

  console.log("\nTrying to write to file");
  try {
    fs.writeFileSync('example.txt', "This file has now been edited.");
  }
  catch (e) {
    console.log("Error Code:", e.code);
  }

  // Grant both read and write permission to user
  console.log("\nGranting read and write access to user");
  fs.chmod("example.txt", 0o600, () => {
    console.log("Trying to write to file");
    fs.writeFileSync('example.txt', "This file has now been edited.");

    console.log("\nReading the file contents");
    console.log(fs.readFileSync("example.txt", 'utf8'));
  });
});

Output:

Granting only read access to user

Reading the file contents
This is an example text file.

Trying to write to file
Error Code: EACCES

Granting read and write access to user
Trying to write to file

Reading the file contents
This file has now been edited.

Example 2: This example shows the usage of string constants and OR operator to give the file permissions.

javascript

// Node.js program to demonstrate the
// fs.chmod() method

// Import the filesystem module
const fs = require('fs');

// Grant only read permission to user
console.log("Granting only read access to user");
fs.chmod("example.txt", fs.constants.S_IRUSR, () => {

  // Reading the file
  console.log("File Contents:", fs.readFileSync("example.txt", 'utf8'));

  // Trying to write to file
  try {
    console.log("\nTrying to write to file");
    fs.writeFileSync('example.txt', "This file now has been edited.");
  }
  catch (e) {
    console.log("Error Occurred, Error Code:", e.code);
  }

  // Granting both read and write permission
  console.log("\nGranting both read and write permission to user");
  fs.chmod("example.txt", fs.constants.S_IRUSR | fs.constants.S_IWUSR, () => {

    // Check the file mode
    console.log("Current File Mode:", fs.statSync("example.txt").mode);

    console.log("Trying to write to file");
    fs.writeFileSync('example.txt', "This file now has been edited.");

    console.log("File Contents:", fs.readFileSync("example.txt", 'utf8'));
  });
});

Output:

Granting only read access to user
File Contents: This file now has been edited.

Trying to write to file
Error Occurred, Error Code: EACCES

Granting both read and write permission to user
Trying to write to file
File Contents: This file now has been edited.

Reference: https://nodejs.org/api/fs.html#fs_fs_chmod_path_mode_callback

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