Node provides a tri-directional popen(3) facility through the\nchild_process module.\n\n
It is possible to stream data through a child's stdin, stdout, and\nstderr in a fully non-blocking way. (Note that some programs use\nline-buffered I/O internally. That doesn't affect node.js but it means\ndata you send to the child process is not immediately consumed.)\n\n
To create a child process use require('child_process').spawn() or\nrequire('child_process').fork(). The semantics of each are slightly\ndifferent, and explained below.\n\n
ChildProcess is an [EventEmitter][].\n\n
Child processes always have three streams associated with them. child.stdin,\nchild.stdout, and child.stderr. These may be shared with the stdio\nstreams of the parent process, or they may be separate stream objects\nwhich can be piped to and from.\n\n
The ChildProcess class is not intended to be used directly. Use the\nspawn() or fork() methods to create a Child Process instance.\n\n
Emitted when:\n\n
\nSee also ChildProcess#kill() and\nChildProcess#send().\n\n
This event is emitted after the child process ends. If the process terminated\nnormally, code is the final exit code of the process, otherwise null. If\nthe process terminated due to receipt of a signal, signal is the string name\nof the signal, otherwise null.\n\n
Note that the child process stdio streams might still be open.\n\n
\nSee waitpid(2).\n\n
This event is emitted when the stdio streams of a child process have all\nterminated. This is distinct from 'exit', since multiple processes\nmight share the same stdio streams.\n\n
\n" }, { "textRaw": "Event: 'disconnect'", "type": "event", "name": "disconnect", "desc": "This event is emitted after using the .disconnect() method in the parent or\nin the child. After disconnecting it is no longer possible to send messages.\nAn alternative way to check if you can send messages is to see if the\nchild.connected property is true.\n\n
Messages send by .send(message, [sendHandle]) are obtained using the\nmessage event.\n\n
A Writable Stream that represents the child process's stdin.\nClosing this stream via end() often causes the child process to terminate.\n\n
If the child stdio streams are shared with the parent, then this will\nnot be set.\n\n
\n" }, { "textRaw": "`stdout` {Stream object} ", "name": "stdout", "desc": "A Readable Stream that represents the child process's stdout.\n\n
If the child stdio streams are shared with the parent, then this will\nnot be set.\n\n
\n" }, { "textRaw": "`stderr` {Stream object} ", "name": "stderr", "desc": "A Readable Stream that represents the child process's stderr.\n\n
If the child stdio streams are shared with the parent, then this will\nnot be set.\n\n
\n" }, { "textRaw": "`pid` {Integer} ", "name": "pid", "desc": "The PID of the child process.\n\n
\nExample:\n\n
\nvar spawn = require('child_process').spawn,\n grep = spawn('grep', ['ssh']);\n\nconsole.log('Spawned child pid: ' + grep.pid);\ngrep.stdin.end();Send a signal to the child process. If no argument is given, the process will\nbe sent 'SIGTERM'. See signal(7) for a list of available signals.\n\n
var spawn = require('child_process').spawn,\n grep = spawn('grep', ['ssh']);\n\ngrep.on('close', function (code, signal) {\n console.log('child process terminated due to receipt of signal '+signal);\n});\n\n// send SIGHUP to process\ngrep.kill('SIGHUP');May emit an 'error' event when the signal cannot be delivered. Sending a\nsignal to a child process that has already exited is not an error but may\nhave unforeseen consequences: if the PID (the process ID) has been reassigned\nto another process, the signal will be delivered to that process instead.\nWhat happens next is anyone's guess.\n\n
Note that while the function is called kill, the signal delivered to the\nchild process may not actually kill it. kill really just sends a signal\nto a process.\n\n
See kill(2)\n\n
When using child_process.fork() you can write to the child using\nchild.send(message, [sendHandle]) and messages are received by\na 'message' event on the child.\n\n
For example:\n\n
\nvar cp = require('child_process');\n\nvar n = cp.fork(__dirname + '/sub.js');\n\nn.on('message', function(m) {\n console.log('PARENT got message:', m);\n});\n\nn.send({ hello: 'world' });And then the child script, 'sub.js' might look like this:\n\n
process.on('message', function(m) {\n console.log('CHILD got message:', m);\n});\n\nprocess.send({ foo: 'bar' });In the child the process object will have a send() method, and process\nwill emit objects each time it receives a message on its channel.\n\n
There is a special case when sending a {cmd: 'NODE_foo'} message. All messages\ncontaining a NODE_ prefix in its cmd property will not be emitted in\nthe message event, since they are internal messages used by node core.\nMessages containing the prefix are emitted in the internalMessage event, you\nshould by all means avoid using this feature, it is subject to change without notice.\n\n
The sendHandle option to child.send() is for sending a TCP server or\nsocket object to another process. The child will receive the object as its\nsecond argument to the message event.\n\n
Emits an 'error' event if the message cannot be sent, for example because\nthe child process has already exited.\n\n
Here is an example of sending a server:\n\n
\nvar child = require('child_process').fork('child.js');\n\n// Open up the server object and send the handle.\nvar server = require('net').createServer();\nserver.on('connection', function (socket) {\n socket.end('handled by parent');\n});\nserver.listen(1337, function() {\n child.send('server', server);\n});And the child would the receive the server object as:\n\n
\nprocess.on('message', function(m, server) {\n if (m === 'server') {\n server.on('connection', function (socket) {\n socket.end('handled by child');\n });\n }\n});Note that the server is now shared between the parent and child, this means\nthat some connections will be handled by the parent and some by the child.\n\n
\nFor dgram servers the workflow is exactly the same. Here you listen on\na message event instead of connection and use server.bind instead of\nserver.listen. (Currently only supported on UNIX platforms.)\n\n
Here is an example of sending a socket. It will spawn two children and handle\nconnections with the remote address 74.125.127.100 as VIP by sending the\nsocket to a "special" child process. Other sockets will go to a "normal" process.\n\n
var normal = require('child_process').fork('child.js', ['normal']);\nvar special = require('child_process').fork('child.js', ['special']);\n\n// Open up the server and send sockets to child\nvar server = require('net').createServer();\nserver.on('connection', function (socket) {\n\n // if this is a VIP\n if (socket.remoteAddress === '74.125.127.100') {\n special.send('socket', socket);\n return;\n }\n // just the usual dudes\n normal.send('socket', socket);\n});\nserver.listen(1337);The child.js could look like this:\n\n
process.on('message', function(m, socket) {\n if (m === 'socket') {\n socket.end('You were handled as a ' + process.argv[2] + ' person');\n }\n});Note that once a single socket has been sent to a child the parent can no\nlonger keep track of when the socket is destroyed. To indicate this condition\nthe .connections property becomes null.\nIt is also recommended not to use .maxConnections in this condition.\n\n
To close the IPC connection between parent and child use the\nchild.disconnect() method. This allows the child to exit gracefully since\nthere is no IPC channel keeping it alive. When calling this method the\ndisconnect event will be emitted in both parent and child, and the\nconnected flag will be set to false. Please note that you can also call\nprocess.disconnect() in the child process.\n\n
Launches a new process with the given command, with command line arguments in args.\nIf omitted, args defaults to an empty Array.\n\n
The third argument is used to specify additional options, which defaults to:\n\n
\n{ cwd: undefined,\n env: process.env\n}cwd allows you to specify the working directory from which the process is spawned.\nUse env to specify environment variables that will be visible to the new process.\n\n
Example of running ls -lh /usr, capturing stdout, stderr, and the exit code:\n\n
var spawn = require('child_process').spawn,\n ls = spawn('ls', ['-lh', '/usr']);\n\nls.stdout.on('data', function (data) {\n console.log('stdout: ' + data);\n});\n\nls.stderr.on('data', function (data) {\n console.log('stderr: ' + data);\n});\n\nls.on('close', function (code) {\n console.log('child process exited with code ' + code);\n});Example: A very elaborate way to run 'ps ax | grep ssh'\n\n
\nvar spawn = require('child_process').spawn,\n ps = spawn('ps', ['ax']),\n grep = spawn('grep', ['ssh']);\n\nps.stdout.on('data', function (data) {\n grep.stdin.write(data);\n});\n\nps.stderr.on('data', function (data) {\n console.log('ps stderr: ' + data);\n});\n\nps.on('close', function (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', function (data) {\n console.log('' + data);\n});\n\ngrep.stderr.on('data', function (data) {\n console.log('grep stderr: ' + data);\n});\n\ngrep.on('close', function (code) {\n if (code !== 0) {\n console.log('grep process exited with code ' + code);\n }\n});Example of checking for failed exec:\n\n
\nvar spawn = require('child_process').spawn,\n child = spawn('bad_command');\n\nchild.stderr.setEncoding('utf8');\nchild.stderr.on('data', function (data) {\n if (/^execvp\\(\\)/.test(data)) {\n console.log('Failed to start child process.');\n }\n});Note that if spawn receives an empty options object, it will result in\nspawning the process with an empty environment rather than using\nprocess.env. This due to backwards compatibility issues with a deprecated\nAPI.\n\n
The 'stdio' option to child_process.spawn() is an array where each\nindex corresponds to a fd in the child. The value is one of the following:\n\n
'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 ChildProcess.stdio[fd]. Pipes created for\nfds 0 - 2 are also available as ChildProcess.stdin, ChildProcess.stdout\nand ChildProcess.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 ChildProcess.send() method.\nIf the child writes JSON messages to this file descriptor, then this will\ntrigger ChildProcess.on('message'). If the child is a Node.js program, then\nthe presence of an IPC channel will enable process.send() and\nprocess.on('message').'ignore' - Do not set this file descriptor in the child. Note that Node\nwill always open fd 0 - 2 for the processes it spawns. When any of these is\nignored node will open /dev/null and attach it to the child's fd.Stream object - Share a readable or writable stream that refers to a tty,\nfile, socket, or a pipe with the child process. The stream's underlying\nfile descriptor is duplicated in the child process to the fd that \ncorresponds to the index in the stdio array.Stream objects can be shared.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'.As a shorthand, the stdio argument may also be one of the following\nstrings, rather than an array:\n\n
ignore - ['ignore', 'ignore', 'ignore']pipe - ['pipe', 'pipe', 'pipe']inherit - [process.stdin, process.stdout, process.stderr] or [0,1,2]Example:\n\n
\nvar spawn = require('child_process').spawn;\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 present a\n// startd-style interface.\nspawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });If the detached option is set, the child process will be made the leader of a\nnew process group. This makes it possible for the child to continue running \nafter the parent exits.\n\n
By default, the parent will wait for the detached child to exit. To prevent\nthe parent from waiting for a given child, use the child.unref() method,\nand the parent's event loop will not include the child in its reference count.\n\n
Example of detaching a long-running process and redirecting its output to a\nfile:\n\n
\n var fs = require('fs'),\n spawn = require('child_process').spawn,\n out = fs.openSync('./out.log', 'a'),\n err = fs.openSync('./out.log', 'a');\n\n var child = spawn('prg', [], {\n detached: true,\n stdio: [ 'ignore', out, err ]\n });\n\n child.unref();When using the detached option to start a long-running process, the process\nwill not stay running in the background unless it is provided with a stdio\nconfiguration that is not connected to the parent. If the parent's stdio is\ninherited, the child will remain attached to the controlling terminal.\n\n
There is a deprecated option called customFds which allows one to specify\nspecific file descriptors for the stdio of the child process. This API was\nnot portable to all platforms and therefore removed.\nWith customFds it was possible to hook up the new process' [stdin, stdout,\nstderr] to existing streams; -1 meant that a new stream should be created.\nUse at your own risk.\n\n
See also: child_process.exec() and child_process.fork()\n\n
Runs a command in a shell and buffers the output.\n\n
\nvar exec = require('child_process').exec,\n child;\n\nchild = exec('cat *.js bad_file | wc -l',\n function (error, stdout, stderr) {\n console.log('stdout: ' + stdout);\n console.log('stderr: ' + stderr);\n if (error !== null) {\n console.log('exec error: ' + error);\n }\n});The callback gets the arguments (error, stdout, stderr). On success, error\nwill be null. On error, error will be an instance of Error and err.code\nwill be the exit code of the child process, and err.signal will be set to the\nsignal that terminated the process.\n\n
There is a second optional argument to specify several options. The\ndefault options are\n\n
\n{ encoding: 'utf8',\n timeout: 0,\n maxBuffer: 200*1024,\n killSignal: 'SIGTERM',\n cwd: null,\n env: null }If timeout is greater than 0, then it will kill the child process\nif it runs longer than timeout milliseconds. The child process is killed with\nkillSignal (default: 'SIGTERM'). maxBuffer specifies the largest\namount of data allowed on stdout or stderr - if this value is exceeded then\nthe child process is killed.\n\n\n
This is similar to child_process.exec() except it does not execute a\nsubshell but rather the specified file directly. This makes it slightly\nleaner than child_process.exec. It has the same options.\n\n\n
This is a special case of the spawn() functionality for spawning Node\nprocesses. In addition to having all the methods in a normal ChildProcess\ninstance, the returned object has a communication channel built-in. See\nchild.send(message, [sendHandle]) for details.\n\n
By default the spawned Node process will have the stdout, stderr associated\nwith the parent's. To change this behavior set the silent property in the\noptions object to true.\n\n
The child process does not automatically exit once it's done, you need to call\nprocess.exit() explicitly. This limitation may be lifted in the future.\n\n
These child Nodes are still whole new instances of V8. Assume at least 30ms\nstartup and 10mb memory for each new Node. That is, you cannot create many\nthousands of them.\n\n
\nThe execPath property in the options object allows for a process to be\ncreated for the child rather than the current node executable. This should be\ndone with care and by default will talk over the fd represented an\nenvironmental variable NODE_CHANNEL_FD on the child process. The input and\noutput on this fd is expected to be line delimited JSON objects.\n\n