child_process(子进程)


稳定性: 2 - 稳定的

源代码: lib/child_process.js

child_process 模块提供了衍生子进程(以一种与 popen(3) 类似但不相同的方式)的能力。 此功能主要由 child_process.spawn() 函数提供:

const { spawn } = require('child_process');
const ls = spawn('ls', ['-lh', '/usr']);

ls.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);
});

ls.stderr.on('data', (data) => {
  console.error(`stderr: ${data}`);
});

ls.on('close', (code) => {
  console.log(`子进程退出,退出码 ${code}`);
});

默认情况下, stdinstdoutstderr 的管道会在父 Node.js 进程和衍生的子进程之间建立。 这些管道具有有限的(且平台特定的)容量。 如果子进程写入 stdout 时超出该限制且没有捕获输出,则子进程会阻塞并等待管道缓冲区接受更多的数据。 这与 shell 中的管道的行为相同。 如果不消费输出,则使用 { stdio: 'ignore' } 选项。

如果 options 对象中有 options.env.PATH 环境变量,则使用它来执行命令查找。 否则,则使用 process.env.PATH

在 Windows 上,环境变量不区分大小写。 Node.js 按字典顺序对 env 的键进行排序,并使用不区分大小写的第一个键。 只有第一个(按字典顺序)条目会被传给子流程。 当传给 env 选项的对象具有多个相同键名的变量时(例如 PATHPath),在 Windows 上可能会出现问题。

child_process.spawn() 方法会异步地衍生子进程,且不阻塞 Node.js 事件循环。 child_process.spawnSync() 函数则以同步的方式提供了等效的功能,但会阻塞事件循环直到衍生的进程退出或被终止。

为方便起见, child_process 模块提供了 child_process.spawn()child_process.spawnSync() 的一些同步和异步的替代方法。 这些替代方法中的每一个都是基于 child_process.spawn()child_process.spawnSync() 实现的。

对于某些用例,例如自动化的 shell 脚本,同步的方法可能更方便。 但是在大多数情况下,同步的方法会对性能产生重大的影响,因为会暂停事件循环直到衍生的进程完成。

Stability: 2 - Stable

Source Code: lib/child_process.js

The child_process module provides the ability to spawn subprocesses in a manner that is similar, but not identical, to popen(3). This capability is primarily provided by the child_process.spawn() function:

const { spawn } = require('child_process');
const ls = spawn('ls', ['-lh', '/usr']);

ls.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);
});

ls.stderr.on('data', (data) => {
  console.error(`stderr: ${data}`);
});

ls.on('close', (code) => {
  console.log(`child process exited with code ${code}`);
});

By default, pipes for stdin, stdout, and stderr are established between the parent Node.js process and the spawned subprocess. These pipes have limited (and platform-specific) capacity. If the subprocess writes to stdout in excess of that limit without the output being captured, the subprocess blocks waiting for the pipe buffer to accept more data. This is identical to the behavior of pipes in the shell. Use the { stdio: 'ignore' } option if the output will not be consumed.

The command lookup is performed using the options.env.PATH environment variable if it is in the options object. Otherwise, process.env.PATH is used.

On Windows, environment variables are case-insensitive. Node.js lexicographically sorts the env keys and uses the first one that case-insensitively matches. Only first (in lexicographic order) entry will be passed to the subprocess. This might lead to issues on Windows when passing objects to the env option that have multiple variants of the same key, such as PATH and Path.

The child_process.spawn() method spawns the child process asynchronously, without blocking the Node.js event loop. The child_process.spawnSync() function provides equivalent functionality in a synchronous manner that blocks the event loop until the spawned process either exits or is terminated.

For convenience, the child_process module provides a handful of synchronous and asynchronous alternatives to child_process.spawn() and child_process.spawnSync(). Each of these alternatives are implemented on top of child_process.spawn() or child_process.spawnSync().

For certain use cases, such as automating shell scripts, the synchronous counterparts may be more convenient. In many cases, however, the synchronous methods can have significant impact on performance due to stalling the event loop while spawned processes complete.