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Build Docs Reference Guides Blog Discord/node:child_process/ChildProcessWithoutNullStreams M[events.captureRejectionSymbol]M[Symbol.dispose]MaddListener Pchannel Pconnected Mdisconnect Memit MeventNames PexitCode MgetMaxListeners Mkill Pkilled MlistenerCount Mlisteners Moff Mon Monce Ppid MprependListener MprependOnceListener MrawListeners Mref MremoveAllListeners MremoveListener Msend MsetMaxListeners PsignalCode Pspawnargs Pspawnfile Pstderr Pstdin Pstdio Pstdout Munref

interface

child_process.ChildProcessWithoutNullStreamsinterface ChildProcessWithoutNullStreamsInstances of the ChildProcess represent spawned child processes.

Instances of ChildProcess are not intended to be created directly. Rather, use the spawn, exec,execFile, or fork methods to create instances of ChildProcess.

readonly channel?: null | ControlThe subprocess.channel property is a reference to the child's IPC channel. If no IPC channel exists, this property is undefined.

readonly connected: booleanThe subprocess.connected property indicates whether it is still possible to send and receive messages from a child process. When subprocess.connected is false, it is no longer possible to send or receive messages.

readonly exitCode: null | numberThe subprocess.exitCode property indicates the exit code of the child process. If the child process is still running, the field will be null.

readonly killed: booleanThe subprocess.killed property indicates whether the child process successfully received a signal from subprocess.kill(). The killed property does not indicate that the child process has been terminated.

readonly pid?: numberReturns the process identifier (PID) of the child process. If the child process fails to spawn due to errors, then the value is undefined and error is emitted.

import { spawn } from 'node:child_process'; const grep = spawn('grep', ['ssh']); console.log(`Spawned child pid: ${grep.pid}`); grep.stdin.end(); readonly signalCode: null | SignalsThe subprocess.signalCode property indicates the signal received by the child process if any, else null.

readonly spawnargs: string[]The subprocess.spawnargs property represents the full list of command-line arguments the child process was launched with.

readonly spawnfile: stringThe subprocess.spawnfile property indicates the executable file name of the child process that is launched.

For fork, its value will be equal to process.execPath. For spawn, its value will be the name of the executable file. For exec, its value will be the name of the shell in which the child process is launched.

stderr: ReadableA Readable Stream that represents the child process's stderr.

If the child was spawned with stdio[2] set to anything other than 'pipe', then this will be null.

subprocess.stderr is an alias for subprocess.stdio[2]. Both properties will refer to the same value.

The subprocess.stderr property can be null or undefined if the child process could not be successfully spawned.

stdin: WritableA Writable Stream that represents the child process's stdin.

If a child process waits to read all of its input, the child will not continue until this stream has been closed via end().

If the child was spawned with stdio[0] set to anything other than 'pipe', then this will be null.

subprocess.stdin is an alias for subprocess.stdio[0]. Both properties will refer to the same value.

The subprocess.stdin property can be null or undefined if the child process could not be successfully spawned.

readonly stdio: [Writable, Readable, Readable, undefined | null | Writable | Readable, undefined | null | Writable | Readable]A sparse array of pipes to the child process, corresponding with positions in the stdio option passed to spawn that have been set to the value 'pipe'. subprocess.stdio[0], subprocess.stdio[1], and subprocess.stdio[2] are also available as subprocess.stdin, subprocess.stdout, and subprocess.stderr, respectively.

In the following example, only the child's fd 1 (stdout) is configured as a pipe, so only the parent's subprocess.stdio[1] is a stream, all other values in the array are null.

import assert from 'node:assert'; import fs from 'node:fs'; import child_process from 'node:child_process'; const subprocess = child_process.spawn('ls', { stdio: [ 0, // Use parent's stdin for child. 'pipe', // Pipe child's stdout to parent. fs.openSync('err.out', 'w'), // Direct child's stderr to a file. ], }); assert.strictEqual(subprocess.stdio[0], null); assert.strictEqual(subprocess.stdio[0], subprocess.stdin); assert(subprocess.stdout); assert.strictEqual(subprocess.stdio[1], subprocess.stdout); assert.strictEqual(subprocess.stdio[2], null); assert.strictEqual(subprocess.stdio[2], subprocess.stderr); The subprocess.stdio property can be undefined if the child process could not be successfully spawned.

{ console.log(`Received chunk ${data}`); }); ``` The `subprocess.stdout` property can be `null` or `undefined` if the child process could not be successfully spawned." data-algolia-static="false" data-algolia-merged="false" data-type="Property">stdout: ReadableA Readable Stream that represents the child process's stdout.

If the child was spawned with stdio[1] set to anything other than 'pipe', then this will be null.

subprocess.stdout is an alias for subprocess.stdio[1]. Both properties will refer to the same value.

import { spawn } from 'node:child_process'; const subprocess = spawn('ls'); subprocess.stdout.on('data', (data) => { console.log(`Received chunk ${data}`); }); The subprocess.stdout property can be null or undefined if the child process could not be successfully spawned.

[events.captureRejectionSymbol](error: Error,event: string | symbol,...args: any[]): void;The Symbol.for('nodejs.rejection') method is called in case a promise rejection happens when emitting an event and captureRejections is enabled on the emitter. It is possible to use events.captureRejectionSymbol in place of Symbol.for('nodejs.rejection').

import { EventEmitter, captureRejectionSymbol } from 'node:events'; class MyClass extends EventEmitter { constructor() { super({ captureRejections: true }); } [captureRejectionSymbol](err, event, ...args) { console.log('rejection happened for', event, 'with', err, ...args); this.destroy(err); } destroy(err) { // Tear the resource down here. } } [Symbol.dispose](): void;Calls ChildProcess.kill with 'SIGTERM'.

addListenerE extends keyof ChildProcessEventMap>(eventName: E,listener: (...args: ChildProcessEventMap[E]) => void): this;Alias for emitter.on(eventName, listener).

addListener(eventName: string | symbol,listener: (...args: any[]) => void): this;Alias for emitter.on(eventName, listener).

disconnect(): void;Closes the IPC channel between parent and child, allowing the child to exit gracefully once there are no other connections keeping it alive. After calling this method the subprocess.connected and process.connected properties in both the parent and child (respectively) will be set to false, and it will be no longer possible to pass messages between the processes.

The 'disconnect' event will be emitted when there are no messages in the process of being received. This will most often be triggered immediately after calling subprocess.disconnect().

When the child process is a Node.js instance (e.g. spawned using fork), the process.disconnect() method can be invoked within the child process to close the IPC channel as well.

emitE extends keyof ChildProcessEventMap>(eventName: E,...args: ChildProcessEventMap[E]): boolean;Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.

Returns true if the event had listeners, false otherwise.

import { EventEmitter } from 'node:events'; const myEmitter = new EventEmitter(); // First listener myEmitter.on('event', function firstListener() { console.log('Helloooo! first listener'); }); // Second listener myEmitter.on('event', function secondListener(arg1, arg2) { console.log(`event with parameters ${arg1}, ${arg2} in second listener`); }); // Third listener myEmitter.on('event', function thirdListener(...args) { const parameters = args.join(', '); console.log(`event with parameters ${parameters} in third listener`); }); console.log(myEmitter.listeners('event')); myEmitter.emit('event', 1, 2, 3, 4, 5); // Prints: // [ // [Function: firstListener], // [Function: secondListener], // [Function: thirdListener] // ] // Helloooo! first listener // event with parameters 1, 2 in second listener // event with parameters 1, 2, 3, 4, 5 in third listener emit(eventName: string | symbol,...args: any[]): boolean;Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.

Returns true if the event had listeners, false otherwise.

import { EventEmitter } from 'node:events'; const myEmitter = new EventEmitter(); // First listener myEmitter.on('event', function firstListener() { console.log('Helloooo! first listener'); }); // Second listener myEmitter.on('event', function secondListener(arg1, arg2) { console.log(`event with parameters ${arg1}, ${arg2} in second listener`); }); // Third listener myEmitter.on('event', function thirdListener(...args) { const parameters = args.join(', '); console.log(`event with parameters ${parameters} in third listener`); }); console.log(myEmitter.listeners('event')); myEmitter.emit('event', 1, 2, 3, 4, 5); // Prints: // [ // [Function: firstListener], // [Function: secondListener], // [Function: thirdListener] // ] // Helloooo! first listener // event with parameters 1, 2 in second listener // event with parameters 1, 2, 3, 4, 5 in third listener {}); myEE.on('bar', () => {}); const sym = Symbol('symbol'); myEE.on(sym, () => {}); console.log(myEE.eventNames()); // Prints: [ 'foo', 'bar', Symbol(symbol) ] ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">eventNames(): string | symbol[];Returns an array listing the events for which the emitter has registered listeners.

import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => {}); myEE.on('bar', () => {}); const sym = Symbol('symbol'); myEE.on(sym, () => {}); console.log(myEE.eventNames()); // Prints: [ 'foo', 'bar', Symbol(symbol) ] getMaxListeners(): number;Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to events.defaultMaxListeners.

{ console.log( `child process terminated due to receipt of signal ${signal}`); }); // Send SIGHUP to process. grep.kill('SIGHUP'); ``` The `ChildProcess` object may emit an `'error'` event if the signal cannot be delivered. Sending a signal to a child process that has already exited is not an error but may have unforeseen consequences. Specifically, if the process identifier (PID) has been reassigned to another process, the signal will be delivered to that process instead which can have unexpected results. While the function is called `kill`, the signal delivered to the child process may not actually terminate the process. See [`kill(2)`](http://man7.org/linux/man-pages/man2/kill.2.html) for reference. On Windows, where POSIX signals do not exist, the `signal` argument will be ignored, and the process will be killed forcefully and abruptly (similar to `'SIGKILL'`). See `Signal Events` for more details. On Linux, child processes of child processes will not be terminated when attempting to kill their parent. This is likely to happen when running a new process in a shell or with the use of the `shell` option of `ChildProcess`: ```js 'use strict'; import { spawn } from 'node:child_process'; const subprocess = spawn( 'sh', [ '-c', `node -e "setInterval(() => { console.log(process.pid, 'is alive') }, 500);"`, ], { stdio: ['inherit', 'inherit', 'inherit'], }, ); setTimeout(() => { subprocess.kill(); // Does not terminate the Node.js process in the shell. }, 2000); ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">kill(signal?: number | Signals): boolean;The subprocess.kill() method sends a signal to the child process. If no argument is given, the process will be sent the 'SIGTERM' signal. See signal(7) for a list of available signals. This function returns true if kill(2) succeeds, and false otherwise.

import { spawn } from 'node:child_process'; const grep = spawn('grep', ['ssh']); grep.on('close', (code, signal) => { console.log( `child process terminated due to receipt of signal ${signal}`); }); // Send SIGHUP to process. grep.kill('SIGHUP'); The ChildProcess object may emit an 'error' event if the signal cannot be delivered. Sending a signal to a child process that has already exited is not an error but may have unforeseen consequences. Specifically, if the process identifier (PID) has been reassigned to another process, the signal will be delivered to that process instead which can have unexpected results.

While the function is called kill, the signal delivered to the child process may not actually terminate the process.

See kill(2) for reference.

On Windows, where POSIX signals do not exist, the signal argument will be ignored, and the process will be killed forcefully and abruptly (similar to 'SIGKILL'). See Signal Events for more details.

On Linux, child processes of child processes will not be terminated when attempting to kill their parent. This is likely to happen when running a new process in a shell or with the use of the shell option of ChildProcess:

'use strict'; import { spawn } from 'node:child_process'; const subprocess = spawn( 'sh', [ '-c', `node -e "setInterval(() => { console.log(process.pid, 'is alive') }, 500);"`, ], { stdio: ['inherit', 'inherit', 'inherit'], }, ); setTimeout(() => { subprocess.kill(); // Does not terminate the Node.js process in the shell. }, 2000); listenerCountE extends keyof ChildProcessEventMap>(eventName: E,listener?: (...args: ChildProcessEventMap[E]) => void): number;Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.

@param eventNameThe name of the event being listened for

@param listenerThe event handler function

listenerCount(eventName: string | symbol,listener?: (...args: any[]) => void): number;Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.

@param eventNameThe name of the event being listened for

@param listenerThe event handler function

{ console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ] ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">listenersE extends keyof ChildProcessEventMap>(eventName: E): (...args: ChildProcessEventMap[E]) => void[];Returns a copy of the array of listeners for the event named eventName.

server.on('connection', (stream) => { console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ] listeners(eventName: string | symbol): (...args: any[]) => void[];Returns a copy of the array of listeners for the event named eventName.

server.on('connection', (stream) => { console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ] offE extends keyof ChildProcessEventMap>(eventName: E,listener: (...args: ChildProcessEventMap[E]) => void): this;Alias for emitter.removeListener().

off(eventName: string | symbol,listener: (...args: any[]) => void): this;Alias for emitter.removeListener().

{ console.log('someone connected!'); }); ``` Returns a reference to the `EventEmitter`, so that calls can be chained. By default, event listeners are invoked in the order they are added. The `emitter.prependListener()` method can be used as an alternative to add the event listener to the beginning of the listeners array. ```js import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">onE extends keyof ChildProcessEventMap>(eventName: E,listener: (...args: ChildProcessEventMap[E]) => void): this;Adds the listener function to the end of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.

server.on('connection', (stream) => { console.log('someone connected!'); }); Returns a reference to the EventEmitter, so that calls can be chained.

By default, event listeners are invoked in the order they are added. The emitter.prependListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.

import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a @param eventNameThe name of the event.