nodejs Node.js fs.fchmod()方法

Node.js fs.fchmod()方法

原文:https://www.geeksforgeeks.org/node-js-fs-fchmod-method/

fs.fchmod()方法用于更改给定文件描述符的权限。这些权限可以使用对应于各自文件模式的字符串常量或八进制数指定为参数。

注意:Windows 平台只支持写权限的更改。它不支持区分用户、组或其他人的权限。

语法:

fs.fchmod( fd, mode, callback )

参数:该方法接受三个参数，如上所述，如下所述:

[FD: It is an integer value that represents the file descriptor of the file whose permissions must be changed.
Mode: Whether it is a string constant or an octal constant indicates the permission to be granted. The logical or operator can be used to separate multiple permissions.
Callback: is a function that will be called when the method is executed.
- err: If the method fails, this error will be thrown.

下面的例子说明了 Node.js 中的 fs.fchmod()方法:

示例 1: 该示例显示了使用字符串常量和或运算符来授予文件权限。

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

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

// Getting the file descriptor
const fd = fs.openSync('example_file.txt', 'r');

// Allowing only read permission
console.log("Giving only read permission to the user");
fs.fchmod(fd, fs.constants.S_IRUSR, (err) => {
  if (err) throw err;

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

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

  // Trying to write to file
  try {
    console.log("Trying to write to file");
    fs.writeFileSync('example_file.txt', "Hello");
  }
  catch (e) {
    console.log("Error Found, Code:", e.code);
  }

  // Allowing both read and write permission
  console.log("\nGiving both read and write "
                + "permission to the user");

  fs.fchmod(fd, fs.constants.S_IRUSR | 
          fs.constants.S_IWUSR, (err) => {
    if (err) throw err;

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

    console.log("Trying to write to file");
    fs.writeFileSync('example_file.txt', 
        "This file has been written over.");

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

输出:

Giving only read permission to the user
Current File Mode: 33024
File Contents: This file has been written over.
Trying to write to file
Error Found, Code: EACCES

Giving both read and write permission to the user
Current File Mode: 33152
Trying to write to file
File Contents: This file has been written over.

示例 2: 该示例显示了八进制常量的用法，以赋予文件权限。

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

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

// Getting the file descriptor
const fd = fs.openSync('example_file.txt', 'r');

// Allowing only read permission
console.log("Giving only read permission to everyone");
fs.fchmod(fd, 0o444, (err) => {
  if (err) throw err;

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

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

  // Trying to write to file
  try {
    console.log("Trying to write to file");
    fs.writeFileSync('example_file.txt', "Hello");
  }
  catch (e) {
    console.log("Error Found, Code:", e.code);
  }

  // Allowing both read and write permission
  console.log("\nGiving both read and write "
                  + "permission to everyone");

  fs.fchmod(fd, 0o666, (err) => {
    if (err) throw err;

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

    console.log("Trying to write to file");
    fs.writeFileSync('example_file.txt', 
        "This file has been written over.");

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

输出:

Giving only read permission to everyone
Current File Mode: 33060
File Contents: This file has been written over.
Trying to write to file
Error Found, Code: EACCES

Giving both read and write permission to everyone
Current File Mode: 33206
Trying to write to file
File Contents: This file has been written over.

参考:https://nodejs . org/API/fs . html # fs _ fs _ fchmod _ FD _ mode _ callback