\n\nStability: 2 - Stable
\n
The child_process module provides the ability to spawn child processes in\na manner that is similar, but not identical, to popen(3). This capability\nis primarily provided by the child_process.spawn() function:
const { spawn } = require('child_process');\nconst ls = spawn('ls', ['-lh', '/usr']);\n\nls.stdout.on('data', (data) => {\n console.log(`stdout: ${data}`);\n});\n\nls.stderr.on('data', (data) => {\n console.log(`stderr: ${data}`);\n});\n\nls.on('close', (code) => {\n console.log(`child process exited with code ${code}`);\n});\nBy default, pipes for stdin, stdout, and stderr are established between\nthe parent Node.js process and the spawned child. These pipes have\nlimited (and platform-specific) capacity. If the child process writes to\nstdout in excess of that limit without the output being captured, the child\nprocess will block waiting for the pipe buffer to accept more data. This is\nidentical to the behavior of pipes in the shell. Use the { stdio: 'ignore' }\noption if the output will not be consumed.
The child_process.spawn() method spawns the child process asynchronously,\nwithout blocking the Node.js event loop. The child_process.spawnSync()\nfunction provides equivalent functionality in a synchronous manner that blocks\nthe event loop until the spawned process either exits or is terminated.
For convenience, the child_process module provides a handful of synchronous\nand asynchronous alternatives to child_process.spawn() and\nchild_process.spawnSync(). Note that each of these alternatives are\nimplemented on top of child_process.spawn() or child_process.spawnSync().
child_process.exec(): spawns a shell and runs a command within that shell,\npassing the stdout and stderr to a callback function when complete.child_process.execFile(): similar to child_process.exec() except that\nit spawns the command directly without first spawning a shell by default.child_process.fork(): spawns a new Node.js process and invokes a\nspecified module with an IPC communication channel established that allows\nsending messages between parent and child.child_process.execSync(): a synchronous version of\nchild_process.exec() that will block the Node.js event loop.child_process.execFileSync(): a synchronous version of\nchild_process.execFile() that will block the Node.js event loop.For certain use cases, such as automating shell scripts, the\nsynchronous counterparts may be more convenient. In many cases, however,\nthe synchronous methods can have significant impact on performance due to\nstalling the event loop while spawned processes complete.
\n", "modules": [ { "textRaw": "Asynchronous Process Creation", "name": "asynchronous_process_creation", "desc": "The child_process.spawn(), child_process.fork(), child_process.exec(),\nand child_process.execFile() methods all follow the idiomatic asynchronous\nprogramming pattern typical of other Node.js APIs.
Each of the methods returns a ChildProcess instance. These objects\nimplement the Node.js EventEmitter API, allowing the parent process to\nregister listener functions that are called when certain events occur during\nthe life cycle of the child process.
The child_process.exec() and child_process.execFile() methods additionally\nallow for an optional callback function to be specified that is invoked\nwhen the child process terminates.
The importance of the distinction between child_process.exec() and\nchild_process.execFile() can vary based on platform. On Unix-type operating\nsystems (Unix, Linux, macOS) child_process.execFile() can be more efficient\nbecause it does not spawn a shell by default. On Windows, however, .bat and .cmd\nfiles are not executable on their own without a terminal, and therefore cannot\nbe launched using child_process.execFile(). When running on Windows, .bat\nand .cmd files can be invoked using child_process.spawn() with the shell\noption set, with child_process.exec(), or by spawning cmd.exe and passing\nthe .bat or .cmd file as an argument (which is what the shell option and\nchild_process.exec() do). In any case, if the script filename contains\nspaces it needs to be quoted.
// On Windows Only ...\nconst { spawn } = require('child_process');\nconst bat = spawn('cmd.exe', ['/c', 'my.bat']);\n\nbat.stdout.on('data', (data) => {\n console.log(data.toString());\n});\n\nbat.stderr.on('data', (data) => {\n console.log(data.toString());\n});\n\nbat.on('exit', (code) => {\n console.log(`Child exited with code ${code}`);\n});\n// OR...\nconst { exec } = require('child_process');\nexec('my.bat', (err, stdout, stderr) => {\n if (err) {\n console.error(err);\n return;\n }\n console.log(stdout);\n});\n\n// Script with spaces in the filename:\nconst bat = spawn('"my script.cmd"', ['a', 'b'], { shell: true });\n// or:\nexec('"my script.cmd" a b', (err, stdout, stderr) => {\n // ...\n});\nSpawns a shell then executes the command within that shell, buffering any\ngenerated output. The command string passed to the exec function is processed\ndirectly by the shell and special characters (vary based on\nshell)\nneed to be dealt with accordingly:
exec('"/path/to/test file/test.sh" arg1 arg2');\n//Double quotes are used so that the space in the path is not interpreted as\n//multiple arguments\n\nexec('echo "The \\\\$HOME variable is $HOME"');\n//The $HOME variable is escaped in the first instance, but not in the second\nNever pass unsanitized user input to this function. Any input containing shell\nmetacharacters may be used to trigger arbitrary command execution.
\nconst { exec } = require('child_process');\nexec('cat *.js bad_file | wc -l', (error, stdout, stderr) => {\n if (error) {\n console.error(`exec error: ${error}`);\n return;\n }\n console.log(`stdout: ${stdout}`);\n console.log(`stderr: ${stderr}`);\n});\nIf a callback function is provided, it is called with the arguments\n(error, stdout, stderr). On success, error will be null. On error,\nerror will be an instance of Error. The error.code property will be\nthe exit code of the child process while error.signal will be set to the\nsignal that terminated the process. Any exit code other than 0 is considered\nto be an error.
The stdout and stderr arguments passed to the callback will contain the\nstdout and stderr output of the child process. By default, Node.js will decode\nthe output as UTF-8 and pass strings to the callback. The encoding option\ncan be used to specify the character encoding used to decode the stdout and\nstderr output. If encoding is 'buffer', or an unrecognized character\nencoding, Buffer objects will be passed to the callback instead.
The options argument may be passed as the second argument to customize how\nthe process is spawned. The default options are:
const defaults = {\n encoding: 'utf8',\n timeout: 0,\n maxBuffer: 200 * 1024,\n killSignal: 'SIGTERM',\n cwd: null,\n env: null\n};\nIf timeout is greater than 0, the parent will send the signal\nidentified by the killSignal property (the default is 'SIGTERM') if the\nchild runs longer than timeout milliseconds.
Unlike the exec(3) POSIX system call, child_process.exec() does not replace\nthe existing process and uses a shell to execute the command.
If this method is invoked as its util.promisify()ed version, it returns\na Promise for an object with stdout and stderr properties. In case of an\nerror (including any error resulting in an exit code other than 0), a rejected\npromise is returned, with the same error object given in the callback, but\nwith an additional two properties stdout and stderr.
const util = require('util');\nconst exec = util.promisify(require('child_process').exec);\n\nasync function lsExample() {\n const { stdout, stderr } = await exec('ls');\n console.log('stdout:', stdout);\n console.log('stderr:', stderr);\n}\nlsExample();\nThe child_process.execFile() function is similar to child_process.exec()\nexcept that it does not spawn a shell by default. Rather, the specified executable file\nis spawned directly as a new process making it slightly more efficient than\nchild_process.exec().
The same options as child_process.exec() are supported. Since a shell is not\nspawned, behaviors such as I/O redirection and file globbing are not supported.
const { execFile } = require('child_process');\nconst child = execFile('node', ['--version'], (error, stdout, stderr) => {\n if (error) {\n throw error;\n }\n console.log(stdout);\n});\nThe stdout and stderr arguments passed to the callback will contain the\nstdout and stderr output of the child process. By default, Node.js will decode\nthe output as UTF-8 and pass strings to the callback. The encoding option\ncan be used to specify the character encoding used to decode the stdout and\nstderr output. If encoding is 'buffer', or an unrecognized character\nencoding, Buffer objects will be passed to the callback instead.
If this method is invoked as its util.promisify()ed version, it returns\na Promise for an object with stdout and stderr properties. In case of an\nerror (including any error resulting in an exit code other than 0), a rejected\npromise is returned, with the same error object given in the\ncallback, but with an additional two properties stdout and stderr.
const util = require('util');\nconst execFile = util.promisify(require('child_process').execFile);\nasync function getVersion() {\n const { stdout } = await execFile('node', ['--version']);\n console.log(stdout);\n}\ngetVersion();\nIf the shell option is enabled, do not pass unsanitized user input to this\nfunction. Any input containing shell metacharacters may be used to trigger\narbitrary command execution.
The child_process.fork() method is a special case of\nchild_process.spawn() used specifically to spawn new Node.js processes.\nLike child_process.spawn(), a ChildProcess object is returned. The returned\nChildProcess will have an additional communication channel built-in that\nallows messages to be passed back and forth between the parent and child. See\nsubprocess.send() for details.
It is important to keep in mind that spawned Node.js child processes are\nindependent of the parent with exception of the IPC communication channel\nthat is established between the two. Each process has its own memory, with\ntheir own V8 instances. Because of the additional resource allocations\nrequired, spawning a large number of child Node.js processes is not\nrecommended.
\nBy default, child_process.fork() will spawn new Node.js instances using the\nprocess.execPath of the parent process. The execPath property in the\noptions object allows for an alternative execution path to be used.
Node.js processes launched with a custom execPath will communicate with the\nparent process using the file descriptor (fd) identified using the\nenvironment variable NODE_CHANNEL_FD on the child process.
Unlike the fork(2) POSIX system call, child_process.fork() does not clone the\ncurrent process.
The shell option available in child_process.spawn() is not supported by\nchild_process.fork() and will be ignored if set.
The child_process.spawn() method spawns a new process using the given\ncommand, with command line arguments in args. If omitted, args defaults\nto an empty array.
If the shell option is enabled, do not pass unsanitized user input to this\nfunction. Any input containing shell metacharacters may be used to trigger\narbitrary command execution.
A third argument may be used to specify additional options, with these defaults:
\nconst defaults = {\n cwd: undefined,\n env: process.env\n};\nUse cwd to specify the working directory from which the process is spawned.\nIf not given, the default is to inherit the current working directory.
Use env to specify environment variables that will be visible to the new\nprocess, the default is process.env.
Example of running ls -lh /usr, capturing stdout, stderr, and the\nexit code:
const { spawn } = require('child_process');\nconst ls = spawn('ls', ['-lh', '/usr']);\n\nls.stdout.on('data', (data) => {\n console.log(`stdout: ${data}`);\n});\n\nls.stderr.on('data', (data) => {\n console.log(`stderr: ${data}`);\n});\n\nls.on('close', (code) => {\n console.log(`child process exited with code ${code}`);\n});\nExample: A very elaborate way to run ps ax | grep ssh
const { spawn } = require('child_process');\nconst ps = spawn('ps', ['ax']);\nconst grep = spawn('grep', ['ssh']);\n\nps.stdout.on('data', (data) => {\n grep.stdin.write(data);\n});\n\nps.stderr.on('data', (data) => {\n console.log(`ps stderr: ${data}`);\n});\n\nps.on('close', (code) => {\n if (code !== 0) {\n console.log(`ps process exited with code ${code}`);\n }\n grep.stdin.end();\n});\n\ngrep.stdout.on('data', (data) => {\n console.log(data.toString());\n});\n\ngrep.stderr.on('data', (data) => {\n console.log(`grep stderr: ${data}`);\n});\n\ngrep.on('close', (code) => {\n if (code !== 0) {\n console.log(`grep process exited with code ${code}`);\n }\n});\nExample of checking for failed spawn:
const { spawn } = require('child_process');\nconst subprocess = spawn('bad_command');\n\nsubprocess.on('error', (err) => {\n console.log('Failed to start subprocess.');\n});\nCertain platforms (macOS, Linux) will use the value of argv[0] for the process\ntitle while others (Windows, SunOS) will use command.
Node.js currently overwrites argv[0] with process.execPath on startup, so\nprocess.argv[0] in a Node.js child process will not match the argv0\nparameter passed to spawn from the parent, retrieve it with the\nprocess.argv0 property instead.
On Windows, setting options.detached to true makes it possible for the\nchild process to continue running after the parent exits. The child will have\nits own console window. Once enabled for a child process, it cannot be\ndisabled.
On non-Windows platforms, if options.detached is set to true, the child\nprocess will be made the leader of a new process group and session. Note that\nchild processes may continue running after the parent exits regardless of\nwhether they are detached or not. See setsid(2) for more information.
By default, the parent will wait for the detached child to exit. To prevent\nthe parent from waiting for a given subprocess, use the subprocess.unref()\nmethod. Doing so will cause the parent's event loop to not include the child in\nits reference count, allowing the parent to exit independently of the child,\nunless there is an established IPC channel between the child and parent.
When using the detached option to start a long-running process, the process\nwill not stay running in the background after the parent exits unless it is\nprovided with a stdio configuration that is not connected to the parent.\nIf the parent's stdio is inherited, the child will remain attached to the\ncontrolling terminal.
Example of a long-running process, by detaching and also ignoring its parent\nstdio file descriptors, in order to ignore the parent's termination:
const { spawn } = require('child_process');\n\nconst subprocess = spawn(process.argv[0], ['child_program.js'], {\n detached: true,\n stdio: 'ignore'\n});\n\nsubprocess.unref();\nAlternatively one can redirect the child process' output into files:
\nconst fs = require('fs');\nconst { spawn } = require('child_process');\nconst out = fs.openSync('./out.log', 'a');\nconst err = fs.openSync('./out.log', 'a');\n\nconst subprocess = spawn('prg', [], {\n detached: true,\n stdio: [ 'ignore', out, err ]\n});\n\nsubprocess.unref();\nThe options.stdio option is used to configure the pipes that are established\nbetween the parent and child process. By default, the child's stdin, stdout,\nand stderr are redirected to corresponding subprocess.stdin,\nsubprocess.stdout, and subprocess.stderr streams on the\nChildProcess object. This is equivalent to setting the options.stdio\nequal to ['pipe', 'pipe', 'pipe'].
For convenience, options.stdio may be one of the following strings:
'pipe' - equivalent to ['pipe', 'pipe', 'pipe'] (the default)'ignore' - equivalent to ['ignore', 'ignore', 'ignore']'inherit' - equivalent to [process.stdin, process.stdout, process.stderr]\n or [0,1,2]Otherwise, the value of options.stdio is an array where each index corresponds\nto an fd in the child. The fds 0, 1, and 2 correspond to stdin, stdout,\nand stderr, respectively. Additional fds can be specified to create additional\npipes between the parent and child. The value is one of the following:
'pipe' - Create a pipe between the child process and the parent process.\nThe parent end of the pipe is exposed to the parent as a property on the\nchild_process object as subprocess.stdio[fd]. Pipes created\nfor fds 0 - 2 are also available as subprocess.stdin,\nsubprocess.stdout and subprocess.stderr, respectively.'ipc' - Create an IPC channel for passing messages/file descriptors\nbetween parent and child. A ChildProcess may have at most one IPC stdio\nfile descriptor. Setting this option enables the subprocess.send()\nmethod. If the child is a Node.js process, the presence of an IPC channel\nwill enable process.send(), process.disconnect(),\nprocess.on('disconnect'), and process.on('message') within the\nchild.
Accessing the IPC channel fd in any way other than process.send()\nor using the IPC channel with a child process that is not a Node.js instance\nis not supported.
'ignore' - Instructs Node.js to ignore the fd in the child. While Node.js\nwill always open fds 0 - 2 for the processes it spawns, setting the fd to\n'ignore' will cause Node.js to open /dev/null and attach it to the\nchild's fd.stdio array. Note that the stream must\nhave an underlying descriptor (file streams do not until the 'open'\nevent has occurred).null, undefined - Use default value. For stdio fds 0, 1, and 2 (in other\nwords, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the\ndefault is 'ignore'.Example:
\nconst { spawn } = require('child_process');\n\n// Child will use parent's stdios\nspawn('prg', [], { stdio: 'inherit' });\n\n// Spawn child sharing only stderr\nspawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });\n\n// Open an extra fd=4, to interact with programs presenting a\n// startd-style interface.\nspawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });\nIt is worth noting that when an IPC channel is established between the\nparent and child processes, and the child is a Node.js process, the child\nis launched with the IPC channel unreferenced (using unref()) until the\nchild registers an event handler for the process.on('disconnect') event\nor the process.on('message') event. This allows the child to exit\nnormally without the process being held open by the open IPC channel.
See also: child_process.exec() and child_process.fork()
The child_process.spawnSync(), child_process.execSync(), and\nchild_process.execFileSync() methods are synchronous and WILL block\nthe Node.js event loop, pausing execution of any additional code until the\nspawned process exits.
Blocking calls like these are mostly useful for simplifying general-purpose\nscripting tasks and for simplifying the loading/processing of application\nconfiguration at startup.
\n", "methods": [ { "textRaw": "child_process.execFileSync(file[, args][, options])", "type": "method", "name": "execFileSync", "meta": { "added": [ "v0.11.12" ], "changes": [ { "version": "v8.8.0", "pr-url": "https://github.com/nodejs/node/pull/15380", "description": "The `windowsHide` option is supported now." }, { "version": "v8.0.0", "pr-url": "https://github.com/nodejs/node/pull/10653", "description": "The `input` option can now be a `Uint8Array`." }, { "version": "v6.2.1, v4.5.0", "pr-url": "https://github.com/nodejs/node/pull/6939", "description": "The `encoding` option can now explicitly be set to `buffer`." } ] }, "signatures": [ { "return": { "textRaw": "Returns: {Buffer|string} The stdout from the command. ", "name": "return", "type": "Buffer|string", "desc": "The stdout from the command." }, "params": [ { "textRaw": "`file` {string} The name or path of the executable file to run. ", "name": "file", "type": "string", "desc": "The name or path of the executable file to run." }, { "textRaw": "`args` {string[]} List of string arguments. ", "name": "args", "type": "string[]", "desc": "List of string arguments.", "optional": true }, { "textRaw": "`options` {Object} ", "options": [ { "textRaw": "`cwd` {string} Current working directory of the child process. ", "name": "cwd", "type": "string", "desc": "Current working directory of the child process." }, { "textRaw": "`input` {string|Buffer|Uint8Array} The value which will be passed as stdin to the spawned process. ", "options": [ { "textRaw": "supplying this value will override `stdio[0]` ", "name": "supplying", "desc": "this value will override `stdio[0]`" } ], "name": "input", "type": "string|Buffer|Uint8Array", "desc": "The value which will be passed as stdin to the spawned process." }, { "textRaw": "`stdio` {string|Array} Child's stdio configuration. **Default:** `'pipe'` ", "options": [ { "textRaw": "`stderr` by default will be output to the parent process' stderr unless `stdio` is specified ", "name": "stderr", "desc": "by default will be output to the parent process' stderr unless `stdio` is specified" } ], "name": "stdio", "type": "string|Array", "desc": "Child's stdio configuration. **Default:** `'pipe'`" }, { "textRaw": "`env` {Object} Environment key-value pairs. ", "name": "env", "type": "Object", "desc": "Environment key-value pairs." }, { "textRaw": "`uid` {number} Sets the user identity of the process (see setuid(2)). ", "name": "uid", "type": "number", "desc": "Sets the user identity of the process (see setuid(2))." }, { "textRaw": "`gid` {number} Sets the group identity of the process (see setgid(2)). ", "name": "gid", "type": "number", "desc": "Sets the group identity of the process (see setgid(2))." }, { "textRaw": "`timeout` {number} In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined` ", "name": "timeout", "type": "number", "desc": "In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined`" }, { "textRaw": "`killSignal` {string|integer} The signal value to be used when the spawned process will be killed. **Default:** `'SIGTERM'` ", "name": "killSignal", "type": "string|integer", "desc": "The signal value to be used when the spawned process will be killed. **Default:** `'SIGTERM'`" }, { "textRaw": "`maxBuffer` {number} Largest amount of data in bytes allowed on stdout or stderr. **Default:** `200*1024` If exceeded, the child process is terminated. See caveat at [`maxBuffer` and Unicode][]. ", "name": "maxBuffer", "type": "number", "desc": "Largest amount of data in bytes allowed on stdout or stderr. **Default:** `200*1024` If exceeded, the child process is terminated. See caveat at [`maxBuffer` and Unicode][]." }, { "textRaw": "`encoding` {string} The encoding used for all stdio inputs and outputs. **Default:** `'buffer'` ", "name": "encoding", "type": "string", "desc": "The encoding used for all stdio inputs and outputs. **Default:** `'buffer'`" }, { "textRaw": "`windowsHide` {boolean} Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`. ", "name": "windowsHide", "type": "boolean", "desc": "Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`." }, { "textRaw": "`shell` {boolean|string} If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on UNIX, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See [Shell Requirements][] and [Default Windows Shell][]. **Default:** `false` (no shell). ", "name": "shell", "type": "boolean|string", "desc": "If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on UNIX, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See [Shell Requirements][] and [Default Windows Shell][]. **Default:** `false` (no shell)." } ], "name": "options", "type": "Object", "optional": true } ] }, { "params": [ { "name": "file" }, { "name": "args", "optional": true }, { "name": "options", "optional": true } ] } ], "desc": "The child_process.execFileSync() method is generally identical to\nchild_process.execFile() with the exception that the method will not return\nuntil the child process has fully closed. When a timeout has been encountered\nand killSignal is sent, the method won't return until the process has\ncompletely exited.
If the child process intercepts and handles the SIGTERM signal and\ndoes not exit, the parent process will still wait until the child process has\nexited.
If the process times out or has a non-zero exit code, this method will\nthrow an Error that will include the full result of the underlying\nchild_process.spawnSync().
If the shell option is enabled, do not pass unsanitized user input to this\nfunction. Any input containing shell metacharacters may be used to trigger\narbitrary command execution.
The child_process.execSync() method is generally identical to\nchild_process.exec() with the exception that the method will not return until\nthe child process has fully closed. When a timeout has been encountered and\nkillSignal is sent, the method won't return until the process has completely\nexited. Note that if the child process intercepts and handles the SIGTERM\nsignal and doesn't exit, the parent process will wait until the child\nprocess has exited.
If the process times out or has a non-zero exit code, this method will\nthrow. The Error object will contain the entire result from\nchild_process.spawnSync()
Never pass unsanitized user input to this function. Any input containing shell\nmetacharacters may be used to trigger arbitrary command execution.
\n" }, { "textRaw": "child_process.spawnSync(command[, args][, options])", "type": "method", "name": "spawnSync", "meta": { "added": [ "v0.11.12" ], "changes": [ { "version": "v8.8.0", "pr-url": "https://github.com/nodejs/node/pull/15380", "description": "The `windowsHide` option is supported now." }, { "version": "v8.0.0", "pr-url": "https://github.com/nodejs/node/pull/10653", "description": "The `input` option can now be a `Uint8Array`." }, { "version": "v6.2.1, v4.5.0", "pr-url": "https://github.com/nodejs/node/pull/6939", "description": "The `encoding` option can now explicitly be set to `buffer`." }, { "version": "v5.7.0", "pr-url": "https://github.com/nodejs/node/pull/4598", "description": "The `shell` option is supported now." } ] }, "signatures": [ { "return": { "textRaw": "Returns: {Object} ", "options": [ { "textRaw": "`pid` {number} Pid of the child process. ", "name": "pid", "type": "number", "desc": "Pid of the child process." }, { "textRaw": "`output` {Array} Array of results from stdio output. ", "name": "output", "type": "Array", "desc": "Array of results from stdio output." }, { "textRaw": "`stdout` {Buffer|string} The contents of `output[1]`. ", "name": "stdout", "type": "Buffer|string", "desc": "The contents of `output[1]`." }, { "textRaw": "`stderr` {Buffer|string} The contents of `output[2]`. ", "name": "stderr", "type": "Buffer|string", "desc": "The contents of `output[2]`." }, { "textRaw": "`status` {number} The exit code of the child process. ", "name": "status", "type": "number", "desc": "The exit code of the child process." }, { "textRaw": "`signal` {string} The signal used to kill the child process. ", "name": "signal", "type": "string", "desc": "The signal used to kill the child process." }, { "textRaw": "`error` {Error} The error object if the child process failed or timed out. ", "name": "error", "type": "Error", "desc": "The error object if the child process failed or timed out." } ], "name": "return", "type": "Object" }, "params": [ { "textRaw": "`command` {string} The command to run. ", "name": "command", "type": "string", "desc": "The command to run." }, { "textRaw": "`args` {Array} List of string arguments. ", "name": "args", "type": "Array", "desc": "List of string arguments.", "optional": true }, { "textRaw": "`options` {Object} ", "options": [ { "textRaw": "`cwd` {string} Current working directory of the child process. ", "name": "cwd", "type": "string", "desc": "Current working directory of the child process." }, { "textRaw": "`input` {string|Buffer|Uint8Array} The value which will be passed as stdin to the spawned process. ", "options": [ { "textRaw": "supplying this value will override `stdio[0]`. ", "name": "supplying", "desc": "this value will override `stdio[0]`." } ], "name": "input", "type": "string|Buffer|Uint8Array", "desc": "The value which will be passed as stdin to the spawned process." }, { "textRaw": "`stdio` {string|Array} Child's stdio configuration. ", "name": "stdio", "type": "string|Array", "desc": "Child's stdio configuration." }, { "textRaw": "`env` {Object} Environment key-value pairs. ", "name": "env", "type": "Object", "desc": "Environment key-value pairs." }, { "textRaw": "`uid` {number} Sets the user identity of the process (see setuid(2)). ", "name": "uid", "type": "number", "desc": "Sets the user identity of the process (see setuid(2))." }, { "textRaw": "`gid` {number} Sets the group identity of the process (see setgid(2)). ", "name": "gid", "type": "number", "desc": "Sets the group identity of the process (see setgid(2))." }, { "textRaw": "`timeout` {number} In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined` ", "name": "timeout", "type": "number", "desc": "In milliseconds the maximum amount of time the process is allowed to run. **Default:** `undefined`" }, { "textRaw": "`killSignal` {string|integer} The signal value to be used when the spawned process will be killed. **Default:** `'SIGTERM'` ", "name": "killSignal", "type": "string|integer", "desc": "The signal value to be used when the spawned process will be killed. **Default:** `'SIGTERM'`" }, { "textRaw": "`maxBuffer` {number} Largest amount of data in bytes allowed on stdout or stderr. **Default:** `200*1024` If exceeded, the child process is terminated. See caveat at [`maxBuffer` and Unicode][]. ", "name": "maxBuffer", "type": "number", "desc": "Largest amount of data in bytes allowed on stdout or stderr. **Default:** `200*1024` If exceeded, the child process is terminated. See caveat at [`maxBuffer` and Unicode][]." }, { "textRaw": "`encoding` {string} The encoding used for all stdio inputs and outputs. **Default:** `'buffer'` ", "name": "encoding", "type": "string", "desc": "The encoding used for all stdio inputs and outputs. **Default:** `'buffer'`" }, { "textRaw": "`shell` {boolean|string} If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on UNIX, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See [Shell Requirements][] and [Default Windows Shell][]. **Default:** `false` (no shell). ", "name": "shell", "type": "boolean|string", "desc": "If `true`, runs `command` inside of a shell. Uses `'/bin/sh'` on UNIX, and `process.env.ComSpec` on Windows. A different shell can be specified as a string. See [Shell Requirements][] and [Default Windows Shell][]. **Default:** `false` (no shell)." }, { "textRaw": "`windowsVerbatimArguments` {boolean} No quoting or escaping of arguments is done on Windows. Ignored on Unix. This is set to `true` automatically when `shell` is specified. **Default:** `false`. ", "name": "windowsVerbatimArguments", "type": "boolean", "desc": "No quoting or escaping of arguments is done on Windows. Ignored on Unix. This is set to `true` automatically when `shell` is specified. **Default:** `false`." }, { "textRaw": "`windowsHide` {boolean} Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`. ", "name": "windowsHide", "type": "boolean", "desc": "Hide the subprocess console window that would normally be created on Windows systems. **Default:** `false`." } ], "name": "options", "type": "Object", "optional": true } ] }, { "params": [ { "name": "command" }, { "name": "args", "optional": true }, { "name": "options", "optional": true } ] } ], "desc": "The child_process.spawnSync() method is generally identical to\nchild_process.spawn() with the exception that the function will not return\nuntil the child process has fully closed. When a timeout has been encountered\nand killSignal is sent, the method won't return until the process has\ncompletely exited. Note that if the process intercepts and handles the\nSIGTERM signal and doesn't exit, the parent process will wait until the child\nprocess has exited.
If the shell option is enabled, do not pass unsanitized user input to this\nfunction. Any input containing shell metacharacters may be used to trigger\narbitrary command execution.
The maxBuffer option specifies the largest number of bytes allowed on stdout\nor stderr. If this value is exceeded, then the child process is terminated.\nThis impacts output that includes multibyte character encodings such as UTF-8 or\nUTF-16. For instance, console.log('中文测试') will send 13 UTF-8 encoded bytes\nto stdout although there are only 4 characters.
The shell should understand the -c switch on UNIX or /d /s /c on Windows.\nOn Windows, command line parsing should be compatible with 'cmd.exe'.
Although Microsoft specifies %COMSPEC% must contain the path to\n'cmd.exe' in the root environment, child processes are not always subject to\nthe same requirement. Thus, in child_process functions where a shell can be\nspawned, 'cmd.exe' is used as a fallback if process.env.ComSpec is\nunavailable.
Instances of the ChildProcess class are EventEmitters that represent\nspawned child processes.
Instances of ChildProcess are not intended to be created directly. Rather,\nuse the child_process.spawn(), child_process.exec(),\nchild_process.execFile(), or child_process.fork() methods to create\ninstances of ChildProcess.
The 'close' event is emitted when the stdio streams of a child process have\nbeen closed. This is distinct from the 'exit' event, since multiple\nprocesses might share the same stdio streams.
The 'disconnect' event is emitted after calling the\nsubprocess.disconnect() method in parent process or\nprocess.disconnect() in child process. After disconnecting it is no longer\npossible to send or receive messages, and the subprocess.connected\nproperty is false.
The 'error' event is emitted whenever:
The 'exit' event may or may not fire after an error has occurred. When\nlistening to both the 'exit' and 'error' events, it is important to guard\nagainst accidentally invoking handler functions multiple times.
See also subprocess.kill() and subprocess.send().
The 'exit' event is emitted after the child process ends. If the process\nexited, code is the final exit code of the process, otherwise null. If the\nprocess terminated due to receipt of a signal, signal is the string name of\nthe signal, otherwise null. One of the two will always be non-null.
Note that when the 'exit' event is triggered, child process stdio streams\nmight still be open.
Also, note that Node.js establishes signal handlers for SIGINT and\nSIGTERM and Node.js processes will not terminate immediately due to receipt\nof those signals. Rather, Node.js will perform a sequence of cleanup actions\nand then will re-raise the handled signal.
See waitpid(2).
\n" }, { "textRaw": "Event: 'message'", "type": "event", "name": "message", "meta": { "added": [ "v0.5.9" ], "changes": [] }, "params": [], "desc": "The 'message' event is triggered when a child process uses process.send()\nto send messages.
The message goes through serialization and parsing. The resulting\nmessage might not be the same as what is originally sent.
\n" } ], "properties": [ { "textRaw": "`channel` {Object} A pipe representing the IPC channel to the child process. ", "type": "Object", "name": "channel", "meta": { "added": [ "v7.1.0" ], "changes": [] }, "desc": "The subprocess.channel property is a reference to the child's IPC channel. If\nno IPC channel currently exists, this property is undefined.
The subprocess.connected property indicates whether it is still possible to\nsend and receive messages from a child process. When subprocess.connected is\nfalse, it is no longer possible to send or receive messages.
The subprocess.killed property indicates whether the child process\nsuccessfully received a signal from subprocess.kill(). The killed property\ndoes not indicate that the child process has been terminated.
Returns the process identifier (PID) of the child process.
\nExample:
\nconst { spawn } = require('child_process');\nconst grep = spawn('grep', ['ssh']);\n\nconsole.log(`Spawned child pid: ${grep.pid}`);\ngrep.stdin.end();\nA Readable Stream that represents the child process's stderr.
If the child was spawned with stdio[2] set to anything other than 'pipe',\nthen this will be null.
subprocess.stderr is an alias for subprocess.stdio[2]. Both properties will\nrefer to the same value.
A Writable Stream that represents the child process's stdin.
Note that if a child process waits to read all of its input, the child will not\ncontinue until this stream has been closed via end().
If the child was spawned with stdio[0] set to anything other than 'pipe',\nthen this will be null.
subprocess.stdin is an alias for subprocess.stdio[0]. Both properties will\nrefer to the same value.
A sparse array of pipes to the child process, corresponding with positions in\nthe stdio option passed to child_process.spawn() that have been set\nto the value 'pipe'. Note that subprocess.stdio[0], subprocess.stdio[1],\nand subprocess.stdio[2] are also available as subprocess.stdin,\nsubprocess.stdout, and subprocess.stderr, respectively.
In the following example, only the child's fd 1 (stdout) is configured as a\npipe, so only the parent's subprocess.stdio[1] is a stream, all other values\nin the array are null.
const assert = require('assert');\nconst fs = require('fs');\nconst child_process = require('child_process');\n\nconst subprocess = child_process.spawn('ls', {\n stdio: [\n 0, // Use parent's stdin for child\n 'pipe', // Pipe child's stdout to parent\n fs.openSync('err.out', 'w') // Direct child's stderr to a file\n ]\n});\n\nassert.strictEqual(subprocess.stdio[0], null);\nassert.strictEqual(subprocess.stdio[0], subprocess.stdin);\n\nassert(subprocess.stdout);\nassert.strictEqual(subprocess.stdio[1], subprocess.stdout);\n\nassert.strictEqual(subprocess.stdio[2], null);\nassert.strictEqual(subprocess.stdio[2], subprocess.stderr);\nA Readable Stream that represents the child process's stdout.
If the child was spawned with stdio[1] set to anything other than 'pipe',\nthen this will be null.
subprocess.stdout is an alias for subprocess.stdio[1]. Both properties will\nrefer to the same value.
Closes the IPC channel between parent and child, allowing the child to exit\ngracefully once there are no other connections keeping it alive. After calling\nthis method the subprocess.connected and process.connected properties in\nboth the parent and child (respectively) will be set to false, and it will be\nno longer possible to pass messages between the processes.
The 'disconnect' event will be emitted when there are no messages in the\nprocess of being received. This will most often be triggered immediately after\ncalling subprocess.disconnect().
Note that when the child process is a Node.js instance (e.g. spawned using\nchild_process.fork()), the process.disconnect() method can be invoked\nwithin the child process to close the IPC channel as well.
The subprocess.kill() method sends a signal to the child process. If no\nargument is given, the process will be sent the 'SIGTERM' signal. See\nsignal(7) for a list of available signals.
const { spawn } = require('child_process');\nconst grep = spawn('grep', ['ssh']);\n\ngrep.on('close', (code, signal) => {\n console.log(\n `child process terminated due to receipt of signal ${signal}`);\n});\n\n// Send SIGHUP to process\ngrep.kill('SIGHUP');\nThe ChildProcess object may emit an 'error' event if the signal cannot be\ndelivered. Sending a signal to a child process that has already exited is not\nan error but may have unforeseen consequences. Specifically, if the process\nidentifier (PID) has been reassigned to another process, the signal will be\ndelivered to that process instead which can have unexpected results.
Note that while the function is called kill, the signal delivered to the\nchild process may not actually terminate the process.
See kill(2) for reference.
\nAlso note: on Linux, child processes of child processes will not be terminated\nwhen attempting to kill their parent. This is likely to happen when running a\nnew process in a shell or with use of the shell option of ChildProcess, such\nas in this example:
'use strict';\nconst { spawn } = require('child_process');\n\nconst subprocess = spawn(\n 'sh',\n [\n '-c',\n `node -e "setInterval(() => {\n console.log(process.pid, 'is alive')\n }, 500);"`\n ], {\n stdio: ['inherit', 'inherit', 'inherit']\n }\n);\n\nsetTimeout(() => {\n subprocess.kill(); // does not terminate the node process in the shell\n}, 2000);\nWhen an IPC channel has been established between the parent and child (\ni.e. when using child_process.fork()), the subprocess.send() method can\nbe used to send messages to the child process. When the child process is a\nNode.js instance, these messages can be received via the\nprocess.on('message') event.
The message goes through serialization and parsing. The resulting\nmessage might not be the same as what is originally sent.
\nFor example, in the parent script:
\nconst cp = require('child_process');\nconst n = cp.fork(`${__dirname}/sub.js`);\n\nn.on('message', (m) => {\n console.log('PARENT got message:', m);\n});\n\n// Causes the child to print: CHILD got message: { hello: 'world' }\nn.send({ hello: 'world' });\nAnd then the child script, 'sub.js' might look like this:
process.on('message', (m) => {\n console.log('CHILD got message:', m);\n});\n\n// Causes the parent to print: PARENT got message: { foo: 'bar', baz: null }\nprocess.send({ foo: 'bar', baz: NaN });\nChild Node.js processes will have a process.send() method of their own that\nallows the child to send messages back to the parent.
There is a special case when sending a {cmd: 'NODE_foo'} message. Messages\ncontaining a NODE_ prefix in the cmd property are reserved for use within\nNode.js core and will not be emitted in the child's process.on('message')\nevent. Rather, such messages are emitted using the\nprocess.on('internalMessage') event and are consumed internally by Node.js.\nApplications should avoid using such messages or listening for\n'internalMessage' events as it is subject to change without notice.
The optional sendHandle argument that may be passed to subprocess.send() is\nfor passing a TCP server or socket object to the child process. The child will\nreceive the object as the second argument passed to the callback function\nregistered on the process.on('message') event. Any data that is received\nand buffered in the socket will not be sent to the child.
The options argument, if present, is an object used to parameterize the\nsending of certain types of handles. options supports the following\nproperties:
keepOpen - A Boolean value that can be used when passing instances of\nnet.Socket. When true, the socket is kept open in the sending process.\nDefaults to false.The optional callback is a function that is invoked after the message is\nsent but before the child may have received it. The function is called with a\nsingle argument: null on success, or an Error object on failure.
If no callback function is provided and the message cannot be sent, an\n'error' event will be emitted by the ChildProcess object. This can happen,\nfor instance, when the child process has already exited.
subprocess.send() will return false if the channel has closed or when the\nbacklog of unsent messages exceeds a threshold that makes it unwise to send\nmore. Otherwise, the method returns true. The callback function can be\nused to implement flow control.
The sendHandle argument can be used, for instance, to pass the handle of\na TCP server object to the child process as illustrated in the example below:
const subprocess = require('child_process').fork('subprocess.js');\n\n// Open up the server object and send the handle.\nconst server = require('net').createServer();\nserver.on('connection', (socket) => {\n socket.end('handled by parent');\n});\nserver.listen(1337, () => {\n subprocess.send('server', server);\n});\nThe child would then receive the server object as:
\nprocess.on('message', (m, server) => {\n if (m === 'server') {\n server.on('connection', (socket) => {\n socket.end('handled by child');\n });\n }\n});\nOnce the server is now shared between the parent and child, some connections\ncan be handled by the parent and some by the child.
\nWhile the example above uses a server created using the net module, dgram\nmodule servers use exactly the same workflow with the exceptions of listening on\na 'message' event instead of 'connection' and using server.bind() instead of\nserver.listen(). This is, however, currently only supported on UNIX platforms.
Similarly, the sendHandler argument can be used to pass the handle of a\nsocket to the child process. The example below spawns two children that each\nhandle connections with "normal" or "special" priority:
const { fork } = require('child_process');\nconst normal = fork('subprocess.js', ['normal']);\nconst special = fork('subprocess.js', ['special']);\n\n// Open up the server and send sockets to child. Use pauseOnConnect to prevent\n// the sockets from being read before they are sent to the child process.\nconst server = require('net').createServer({ pauseOnConnect: true });\nserver.on('connection', (socket) => {\n\n // If this is special priority\n if (socket.remoteAddress === '74.125.127.100') {\n special.send('socket', socket);\n return;\n }\n // This is normal priority\n normal.send('socket', socket);\n});\nserver.listen(1337);\nThe subprocess.js would receive the socket handle as the second argument\npassed to the event callback function:
process.on('message', (m, socket) => {\n if (m === 'socket') {\n if (socket) {\n // Check that the client socket exists.\n // It is possible for the socket to be closed between the time it is\n // sent and the time it is received in the child process.\n socket.end(`Request handled with ${process.argv[2]} priority`);\n }\n }\n});\nOnce a socket has been passed to a child, the parent is no longer capable of\ntracking when the socket is destroyed. To indicate this, the .connections\nproperty becomes null. It is recommended not to use .maxConnections when\nthis occurs.
It is also recommended that any 'message' handlers in the child process\nverify that socket exists, as the connection may have been closed during the\ntime it takes to send the connection to the child.