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| <h1>Node.js v0.10.24 Manual & Documentation</h1> |
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| <p> |
| <a href="index.html" name="toc">Index</a> | |
| <a href="all.html">View on single page</a> | |
| <a href="child_process.json">View as JSON</a> |
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| <div id="toc"> |
| <h2>Table of Contents</h2> |
| <ul> |
| <li><a href="#child_process_child_process">Child Process</a><ul> |
| <li><a href="#child_process_class_childprocess">Class: ChildProcess</a><ul> |
| <li><a href="#child_process_event_error">Event: 'error'</a></li> |
| <li><a href="#child_process_event_exit">Event: 'exit'</a></li> |
| <li><a href="#child_process_event_close">Event: 'close'</a></li> |
| <li><a href="#child_process_event_disconnect">Event: 'disconnect'</a></li> |
| <li><a href="#child_process_event_message">Event: 'message'</a></li> |
| <li><a href="#child_process_child_stdin">child.stdin</a></li> |
| <li><a href="#child_process_child_stdout">child.stdout</a></li> |
| <li><a href="#child_process_child_stderr">child.stderr</a></li> |
| <li><a href="#child_process_child_pid">child.pid</a></li> |
| <li><a href="#child_process_child_connected">child.connected</a></li> |
| <li><a href="#child_process_child_kill_signal">child.kill([signal])</a></li> |
| <li><a href="#child_process_child_send_message_sendhandle">child.send(message, [sendHandle])</a><ul> |
| <li><a href="#child_process_example_sending_server_object">Example: sending server object</a></li> |
| <li><a href="#child_process_example_sending_socket_object">Example: sending socket object</a></li> |
| </ul> |
| </li> |
| <li><a href="#child_process_child_disconnect">child.disconnect()</a></li> |
| </ul> |
| </li> |
| <li><a href="#child_process_child_process_spawn_command_args_options">child_process.spawn(command, [args], [options])</a></li> |
| <li><a href="#child_process_child_process_exec_command_options_callback">child_process.exec(command, [options], callback)</a></li> |
| <li><a href="#child_process_child_process_execfile_file_args_options_callback">child_process.execFile(file, args, options, callback)</a></li> |
| <li><a href="#child_process_child_process_fork_modulepath_args_options">child_process.fork(modulePath, [args], [options])</a></li> |
| </ul> |
| </li> |
| </ul> |
| |
| </div> |
| |
| <div id="apicontent"> |
| <h1>Child Process<span><a class="mark" href="#child_process_child_process" id="child_process_child_process">#</a></span></h1> |
| <pre class="api_stability_3">Stability: 3 - Stable</pre><p>Node provides a tri-directional <code>popen(3)</code> facility through the |
| <code>child_process</code> module. |
| |
| </p> |
| <p>It is possible to stream data through a child's <code>stdin</code>, <code>stdout</code>, and |
| <code>stderr</code> in a fully non-blocking way. (Note that some programs use |
| line-buffered I/O internally. That doesn't affect node.js but it means |
| data you send to the child process is not immediately consumed.) |
| |
| </p> |
| <p>To create a child process use <code>require('child_process').spawn()</code> or |
| <code>require('child_process').fork()</code>. The semantics of each are slightly |
| different, and explained below. |
| |
| </p> |
| <h2>Class: ChildProcess<span><a class="mark" href="#child_process_class_childprocess" id="child_process_class_childprocess">#</a></span></h2> |
| <p><code>ChildProcess</code> is an <a href="events.html#events_class_events_eventemitter">EventEmitter</a>. |
| |
| </p> |
| <p>Child processes always have three streams associated with them. <code>child.stdin</code>, |
| <code>child.stdout</code>, and <code>child.stderr</code>. These may be shared with the stdio |
| streams of the parent process, or they may be separate stream objects |
| which can be piped to and from. |
| |
| </p> |
| <p>The ChildProcess class is not intended to be used directly. Use the |
| <code>spawn()</code> or <code>fork()</code> methods to create a Child Process instance. |
| |
| </p> |
| <h3>Event: 'error'<span><a class="mark" href="#child_process_event_error" id="child_process_event_error">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><code>err</code> <span class="type">Error Object</span> the error.</li> |
| </div></ul> |
| <p>Emitted when: |
| |
| </p> |
| <ol> |
| <li>The process could not be spawned, or</li> |
| <li>The process could not be killed, or</li> |
| <li>Sending a message to the child process failed for whatever reason.</li> |
| </ol> |
| <p>Note that the <code>exit</code>-event may or may not fire after an error has occured. If |
| you are listening on both events to fire a function, remember to guard against |
| calling your function twice. |
| |
| </p> |
| <p>See also <a href="#child_process_child_kill_signal"><code>ChildProcess#kill()</code></a> and |
| <a href="#child_process_child_send_message_sendhandle"><code>ChildProcess#send()</code></a>. |
| |
| </p> |
| <h3>Event: 'exit'<span><a class="mark" href="#child_process_event_exit" id="child_process_event_exit">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><code>code</code> <span class="type">Number</span> the exit code, if it exited normally.</li> |
| <li><code>signal</code> <span class="type">String</span> the signal passed to kill the child process, if it |
| was killed by the parent.</li> |
| </div></ul> |
| <p>This event is emitted after the child process ends. If the process terminated |
| normally, <code>code</code> is the final exit code of the process, otherwise <code>null</code>. If |
| the process terminated due to receipt of a signal, <code>signal</code> is the string name |
| of the signal, otherwise <code>null</code>. |
| |
| </p> |
| <p>Note that the child process stdio streams might still be open. |
| |
| </p> |
| <p>Also, note that node establishes signal handlers for <code>'SIGINT'</code> and <code>'SIGTERM</code>', |
| so it will not terminate due to receipt of those signals, it will exit. |
| |
| </p> |
| <p>See <code>waitpid(2)</code>. |
| |
| </p> |
| <h3>Event: 'close'<span><a class="mark" href="#child_process_event_close" id="child_process_event_close">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><code>code</code> <span class="type">Number</span> the exit code, if it exited normally.</li> |
| <li><code>signal</code> <span class="type">String</span> the signal passed to kill the child process, if it |
| was killed by the parent.</li> |
| </div></ul> |
| <p>This event is emitted when the stdio streams of a child process have all |
| terminated. This is distinct from 'exit', since multiple processes |
| might share the same stdio streams. |
| |
| </p> |
| <h3>Event: 'disconnect'<span><a class="mark" href="#child_process_event_disconnect" id="child_process_event_disconnect">#</a></span></h3> |
| <p>This event is emitted after calling the <code>.disconnect()</code> method in the parent |
| or in the child. After disconnecting it is no longer possible to send messages, |
| and the <code>.connected</code> property is false. |
| |
| </p> |
| <h3>Event: 'message'<span><a class="mark" href="#child_process_event_message" id="child_process_event_message">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><code>message</code> <span class="type">Object</span> a parsed JSON object or primitive value</li> |
| <li><code>sendHandle</code> <span class="type">Handle object</span> a Socket or Server object</li> |
| </div></ul> |
| <p>Messages send by <code>.send(message, [sendHandle])</code> are obtained using the |
| <code>message</code> event. |
| |
| </p> |
| <h3>child.stdin<span><a class="mark" href="#child_process_child_stdin" id="child_process_child_stdin">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><span class="type">Stream object</span></li> |
| </div></ul> |
| <p>A <code>Writable Stream</code> that represents the child process's <code>stdin</code>. |
| Closing this stream via <code>end()</code> often causes the child process to terminate. |
| |
| </p> |
| <p>If the child stdio streams are shared with the parent, then this will |
| not be set. |
| |
| </p> |
| <h3>child.stdout<span><a class="mark" href="#child_process_child_stdout" id="child_process_child_stdout">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><span class="type">Stream object</span></li> |
| </div></ul> |
| <p>A <code>Readable Stream</code> that represents the child process's <code>stdout</code>. |
| |
| </p> |
| <p>If the child stdio streams are shared with the parent, then this will |
| not be set. |
| |
| </p> |
| <h3>child.stderr<span><a class="mark" href="#child_process_child_stderr" id="child_process_child_stderr">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><span class="type">Stream object</span></li> |
| </div></ul> |
| <p>A <code>Readable Stream</code> that represents the child process's <code>stderr</code>. |
| |
| </p> |
| <p>If the child stdio streams are shared with the parent, then this will |
| not be set. |
| |
| </p> |
| <h3>child.pid<span><a class="mark" href="#child_process_child_pid" id="child_process_child_pid">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><span class="type">Integer</span></li> |
| </div></ul> |
| <p>The PID of the child process. |
| |
| </p> |
| <p>Example: |
| |
| </p> |
| <pre><code>var spawn = require('child_process').spawn, |
| grep = spawn('grep', ['ssh']); |
| |
| console.log('Spawned child pid: ' + grep.pid); |
| grep.stdin.end();</code></pre> |
| <h3>child.connected<span><a class="mark" href="#child_process_child_connected" id="child_process_child_connected">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><span class="type">Boolean</span> Set to false after `.disconnect' is called</li> |
| </div></ul> |
| <p>If <code>.connected</code> is false, it is no longer possible to send messages. |
| |
| </p> |
| <h3>child.kill([signal])<span><a class="mark" href="#child_process_child_kill_signal" id="child_process_child_kill_signal">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><code>signal</code> <span class="type">String</span></li> |
| </div></ul> |
| <p>Send a signal to the child process. If no argument is given, the process will |
| be sent <code>'SIGTERM'</code>. See <code>signal(7)</code> for a list of available signals. |
| |
| </p> |
| <pre><code>var spawn = require('child_process').spawn, |
| grep = spawn('grep', ['ssh']); |
| |
| grep.on('close', function (code, signal) { |
| console.log('child process terminated due to receipt of signal '+signal); |
| }); |
| |
| // send SIGHUP to process |
| grep.kill('SIGHUP');</code></pre> |
| <p>May emit an <code>'error'</code> event when 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: if the PID (the process ID) has been reassigned |
| to another process, the signal will be delivered to that process instead. |
| What happens next is anyone's guess. |
| |
| </p> |
| <p>Note that while the function is called <code>kill</code>, the signal delivered to the |
| child process may not actually kill it. <code>kill</code> really just sends a signal |
| to a process. |
| |
| </p> |
| <p>See <code>kill(2)</code> |
| |
| </p> |
| <h3>child.send(message, [sendHandle])<span><a class="mark" href="#child_process_child_send_message_sendhandle" id="child_process_child_send_message_sendhandle">#</a></span></h3> |
| <div class="signature"><ul> |
| <li><code>message</code> <span class="type">Object</span></li> |
| <li><code>sendHandle</code> <span class="type">Handle object</span></li> |
| </div></ul> |
| <p>When using <code>child_process.fork()</code> you can write to the child using |
| <code>child.send(message, [sendHandle])</code> and messages are received by |
| a <code>'message'</code> event on the child. |
| |
| </p> |
| <p>For example: |
| |
| </p> |
| <pre><code>var cp = require('child_process'); |
| |
| var n = cp.fork(__dirname + '/sub.js'); |
| |
| n.on('message', function(m) { |
| console.log('PARENT got message:', m); |
| }); |
| |
| n.send({ hello: 'world' });</code></pre> |
| <p>And then the child script, <code>'sub.js'</code> might look like this: |
| |
| </p> |
| <pre><code>process.on('message', function(m) { |
| console.log('CHILD got message:', m); |
| }); |
| |
| process.send({ foo: 'bar' });</code></pre> |
| <p>In the child the <code>process</code> object will have a <code>send()</code> method, and <code>process</code> |
| will emit objects each time it receives a message on its channel. |
| |
| </p> |
| <p>There is a special case when sending a <code>{cmd: 'NODE_foo'}</code> message. All messages |
| containing a <code>NODE_</code> prefix in its <code>cmd</code> property will not be emitted in |
| the <code>message</code> event, since they are internal messages used by node core. |
| Messages containing the prefix are emitted in the <code>internalMessage</code> event, you |
| should by all means avoid using this feature, it is subject to change without notice. |
| |
| </p> |
| <p>The <code>sendHandle</code> option to <code>child.send()</code> is for sending a TCP server or |
| socket object to another process. The child will receive the object as its |
| second argument to the <code>message</code> event. |
| |
| </p> |
| <p>Emits an <code>'error'</code> event if the message cannot be sent, for example because |
| the child process has already exited. |
| |
| </p> |
| <h4>Example: sending server object<span><a class="mark" href="#child_process_example_sending_server_object" id="child_process_example_sending_server_object">#</a></span></h4> |
| <p>Here is an example of sending a server: |
| |
| </p> |
| <pre><code>var child = require('child_process').fork('child.js'); |
| |
| // Open up the server object and send the handle. |
| var server = require('net').createServer(); |
| server.on('connection', function (socket) { |
| socket.end('handled by parent'); |
| }); |
| server.listen(1337, function() { |
| child.send('server', server); |
| });</code></pre> |
| <p>And the child would the receive the server object as: |
| |
| </p> |
| <pre><code>process.on('message', function(m, server) { |
| if (m === 'server') { |
| server.on('connection', function (socket) { |
| socket.end('handled by child'); |
| }); |
| } |
| });</code></pre> |
| <p>Note that the server is now shared between the parent and child, this means |
| that some connections will be handled by the parent and some by the child. |
| |
| </p> |
| <p>For <code>dgram</code> servers the workflow is exactly the same. Here you listen on |
| a <code>message</code> event instead of <code>connection</code> and use <code>server.bind</code> instead of |
| <code>server.listen</code>. (Currently only supported on UNIX platforms.) |
| |
| </p> |
| <h4>Example: sending socket object<span><a class="mark" href="#child_process_example_sending_socket_object" id="child_process_example_sending_socket_object">#</a></span></h4> |
| <p>Here is an example of sending a socket. It will spawn two children and handle |
| connections with the remote address <code>74.125.127.100</code> as VIP by sending the |
| socket to a "special" child process. Other sockets will go to a "normal" process. |
| |
| </p> |
| <pre><code>var normal = require('child_process').fork('child.js', ['normal']); |
| var special = require('child_process').fork('child.js', ['special']); |
| |
| // Open up the server and send sockets to child |
| var server = require('net').createServer(); |
| server.on('connection', function (socket) { |
| |
| // if this is a VIP |
| if (socket.remoteAddress === '74.125.127.100') { |
| special.send('socket', socket); |
| return; |
| } |
| // just the usual dudes |
| normal.send('socket', socket); |
| }); |
| server.listen(1337);</code></pre> |
| <p>The <code>child.js</code> could look like this: |
| |
| </p> |
| <pre><code>process.on('message', function(m, socket) { |
| if (m === 'socket') { |
| socket.end('You were handled as a ' + process.argv[2] + ' person'); |
| } |
| });</code></pre> |
| <p>Note that once a single socket has been sent to a child the parent can no |
| longer keep track of when the socket is destroyed. To indicate this condition |
| the <code>.connections</code> property becomes <code>null</code>. |
| It is also recommended not to use <code>.maxConnections</code> in this condition. |
| |
| </p> |
| <h3>child.disconnect()<span><a class="mark" href="#child_process_child_disconnect" id="child_process_child_disconnect">#</a></span></h3> |
| <p>Close 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 <code>.connected</code> flag will be set to <code>false</code> in both the parent and |
| child, and it is no longer possible to send messages. |
| |
| </p> |
| <p>The 'disconnect' event will be emitted when there are no messages in the process |
| of being received, most likely immediately. |
| |
| </p> |
| <p>Note that you can also call <code>process.disconnect()</code> in the child process. |
| |
| </p> |
| <h2>child_process.spawn(command, [args], [options])<span><a class="mark" href="#child_process_child_process_spawn_command_args_options" id="child_process_child_process_spawn_command_args_options">#</a></span></h2> |
| <div class="signature"><ul> |
| <li><code>command</code> <span class="type">String</span> The command to run</li> |
| <li><code>args</code> <span class="type">Array</span> List of string arguments</li> |
| <li><code>options</code> <span class="type">Object</span><ul> |
| <li><code>cwd</code> <span class="type">String</span> Current working directory of the child process</li> |
| <li><code>stdio</code> <span class="type">Array|String</span> Child's stdio configuration. (See below)</li> |
| <li><code>customFds</code> <span class="type">Array</span> <strong>Deprecated</strong> File descriptors for the child to use |
| for stdio. (See below)</li> |
| <li><code>env</code> <span class="type">Object</span> Environment key-value pairs</li> |
| <li><code>detached</code> <span class="type">Boolean</span> The child will be a process group leader. (See below)</li> |
| <li><code>uid</code> <span class="type">Number</span> Sets the user identity of the process. (See setuid(2).)</li> |
| <li><code>gid</code> <span class="type">Number</span> Sets the group identity of the process. (See setgid(2).)</li> |
| </ul> |
| </li> |
| <li>return: <span class="type">ChildProcess object</span></li> |
| </div></ul> |
| <p>Launches a new process with the given <code>command</code>, with command line arguments in <code>args</code>. |
| If omitted, <code>args</code> defaults to an empty Array. |
| |
| </p> |
| <p>The third argument is used to specify additional options, which defaults to: |
| |
| </p> |
| <pre><code>{ cwd: undefined, |
| env: process.env |
| }</code></pre> |
| <p><code>cwd</code> allows you to specify the working directory from which the process is spawned. |
| Use <code>env</code> to specify environment variables that will be visible to the new process. |
| |
| </p> |
| <p>Example of running <code>ls -lh /usr</code>, capturing <code>stdout</code>, <code>stderr</code>, and the exit code: |
| |
| </p> |
| <pre><code>var spawn = require('child_process').spawn, |
| ls = spawn('ls', ['-lh', '/usr']); |
| |
| ls.stdout.on('data', function (data) { |
| console.log('stdout: ' + data); |
| }); |
| |
| ls.stderr.on('data', function (data) { |
| console.log('stderr: ' + data); |
| }); |
| |
| ls.on('close', function (code) { |
| console.log('child process exited with code ' + code); |
| });</code></pre> |
| <p>Example: A very elaborate way to run 'ps ax | grep ssh' |
| |
| </p> |
| <pre><code>var spawn = require('child_process').spawn, |
| ps = spawn('ps', ['ax']), |
| grep = spawn('grep', ['ssh']); |
| |
| ps.stdout.on('data', function (data) { |
| grep.stdin.write(data); |
| }); |
| |
| ps.stderr.on('data', function (data) { |
| console.log('ps stderr: ' + data); |
| }); |
| |
| ps.on('close', function (code) { |
| if (code !== 0) { |
| console.log('ps process exited with code ' + code); |
| } |
| grep.stdin.end(); |
| }); |
| |
| grep.stdout.on('data', function (data) { |
| console.log('' + data); |
| }); |
| |
| grep.stderr.on('data', function (data) { |
| console.log('grep stderr: ' + data); |
| }); |
| |
| grep.on('close', function (code) { |
| if (code !== 0) { |
| console.log('grep process exited with code ' + code); |
| } |
| });</code></pre> |
| <p>Example of checking for failed exec: |
| |
| </p> |
| <pre><code>var spawn = require('child_process').spawn, |
| child = spawn('bad_command'); |
| |
| child.stderr.setEncoding('utf8'); |
| child.stderr.on('data', function (data) { |
| if (/^execvp\(\)/.test(data)) { |
| console.log('Failed to start child process.'); |
| } |
| });</code></pre> |
| <p>Note that if spawn receives an empty options object, it will result in |
| spawning the process with an empty environment rather than using |
| <code>process.env</code>. This due to backwards compatibility issues with a deprecated |
| API. |
| |
| </p> |
| <p>The 'stdio' option to <code>child_process.spawn()</code> is an array where each |
| index corresponds to a fd in the child. The value is one of the following: |
| |
| </p> |
| <ol> |
| <li><code>'pipe'</code> - Create a pipe between the child process and the parent process. |
| The parent end of the pipe is exposed to the parent as a property on the |
| <code>child_process</code> object as <code>ChildProcess.stdio[fd]</code>. Pipes created for |
| fds 0 - 2 are also available as ChildProcess.stdin, ChildProcess.stdout |
| and ChildProcess.stderr, respectively.</li> |
| <li><code>'ipc'</code> - Create an IPC channel for passing messages/file descriptors |
| between parent and child. A ChildProcess may have at most <em>one</em> IPC stdio |
| file descriptor. Setting this option enables the ChildProcess.send() method. |
| If the child writes JSON messages to this file descriptor, then this will |
| trigger ChildProcess.on('message'). If the child is a Node.js program, then |
| the presence of an IPC channel will enable process.send() and |
| process.on('message').</li> |
| <li><code>'ignore'</code> - Do not set this file descriptor in the child. Note that Node |
| will always open fd 0 - 2 for the processes it spawns. When any of these is |
| ignored node will open <code>/dev/null</code> and attach it to the child's fd.</li> |
| <li><code>Stream</code> object - Share a readable or writable stream that refers to a tty, |
| file, socket, or a pipe with the child process. The stream's underlying |
| file descriptor is duplicated in the child process to the fd that |
| corresponds to the index in the <code>stdio</code> array.</li> |
| <li>Positive integer - The integer value is interpreted as a file descriptor |
| that is is currently open in the parent process. It is shared with the child |
| process, similar to how <code>Stream</code> objects can be shared.</li> |
| <li><code>null</code>, <code>undefined</code> - Use default value. For stdio fds 0, 1 and 2 (in other |
| words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the |
| default is <code>'ignore'</code>.</li> |
| </ol> |
| <p>As a shorthand, the <code>stdio</code> argument may also be one of the following |
| strings, rather than an array: |
| |
| </p> |
| <ul> |
| <li><code>ignore</code> - <code>['ignore', 'ignore', 'ignore']</code></li> |
| <li><code>pipe</code> - <code>['pipe', 'pipe', 'pipe']</code></li> |
| <li><code>inherit</code> - <code>[process.stdin, process.stdout, process.stderr]</code> or <code>[0,1,2]</code></li> |
| </ul> |
| <p>Example: |
| |
| </p> |
| <pre><code>var spawn = require('child_process').spawn; |
| |
| // Child will use parent's stdios |
| spawn('prg', [], { stdio: 'inherit' }); |
| |
| // Spawn child sharing only stderr |
| spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] }); |
| |
| // Open an extra fd=4, to interact with programs present a |
| // startd-style interface. |
| spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });</code></pre> |
| <p>If the <code>detached</code> option is set, the child process will be made the leader of a |
| new process group. This makes it possible for the child to continue running |
| after the parent exits. |
| |
| </p> |
| <p>By default, the parent will wait for the detached child to exit. To prevent |
| the parent from waiting for a given <code>child</code>, use the <code>child.unref()</code> method, |
| and the parent's event loop will not include the child in its reference count. |
| |
| </p> |
| <p>Example of detaching a long-running process and redirecting its output to a |
| file: |
| |
| </p> |
| <pre><code> var fs = require('fs'), |
| spawn = require('child_process').spawn, |
| out = fs.openSync('./out.log', 'a'), |
| err = fs.openSync('./out.log', 'a'); |
| |
| var child = spawn('prg', [], { |
| detached: true, |
| stdio: [ 'ignore', out, err ] |
| }); |
| |
| child.unref();</code></pre> |
| <p>When using the <code>detached</code> option to start a long-running process, the process |
| will not stay running in the background unless it is provided with a <code>stdio</code> |
| configuration that is not connected to the parent. If the parent's <code>stdio</code> is |
| inherited, the child will remain attached to the controlling terminal. |
| |
| </p> |
| <p>There is a deprecated option called <code>customFds</code> which allows one to specify |
| specific file descriptors for the stdio of the child process. This API was |
| not portable to all platforms and therefore removed. |
| With <code>customFds</code> it was possible to hook up the new process' <code>[stdin, stdout, |
| stderr]</code> to existing streams; <code>-1</code> meant that a new stream should be created. |
| Use at your own risk. |
| |
| </p> |
| <p>See also: <code>child_process.exec()</code> and <code>child_process.fork()</code> |
| |
| </p> |
| <h2>child_process.exec(command, [options], callback)<span><a class="mark" href="#child_process_child_process_exec_command_options_callback" id="child_process_child_process_exec_command_options_callback">#</a></span></h2> |
| <div class="signature"><ul> |
| <li><code>command</code> <span class="type">String</span> The command to run, with space-separated arguments</li> |
| <li><code>options</code> <span class="type">Object</span><ul> |
| <li><code>cwd</code> <span class="type">String</span> Current working directory of the child process</li> |
| <li><code>env</code> <span class="type">Object</span> Environment key-value pairs</li> |
| <li><code>encoding</code> <span class="type">String</span> (Default: 'utf8')</li> |
| <li><code>timeout</code> <span class="type">Number</span> (Default: 0)</li> |
| <li><code>maxBuffer</code> <span class="type">Number</span> (Default: <code>200*1024</code>)</li> |
| <li><code>killSignal</code> <span class="type">String</span> (Default: 'SIGTERM')</li> |
| </ul> |
| </li> |
| <li><code>callback</code> <span class="type">Function</span> called with the output when process terminates<ul> |
| <li><code>error</code> <span class="type">Error</span></li> |
| <li><code>stdout</code> <span class="type">Buffer</span></li> |
| <li><code>stderr</code> <span class="type">Buffer</span></li> |
| </ul> |
| </li> |
| <li>Return: ChildProcess object</li> |
| </div></ul> |
| <p>Runs a command in a shell and buffers the output. |
| |
| </p> |
| <pre><code>var exec = require('child_process').exec, |
| child; |
| |
| child = exec('cat *.js bad_file | wc -l', |
| function (error, stdout, stderr) { |
| console.log('stdout: ' + stdout); |
| console.log('stderr: ' + stderr); |
| if (error !== null) { |
| console.log('exec error: ' + error); |
| } |
| });</code></pre> |
| <p>The callback gets the arguments <code>(error, stdout, stderr)</code>. On success, <code>error</code> |
| will be <code>null</code>. On error, <code>error</code> will be an instance of <code>Error</code> and <code>err.code</code> |
| will be the exit code of the child process, and <code>err.signal</code> will be set to the |
| signal that terminated the process. |
| |
| </p> |
| <p>There is a second optional argument to specify several options. The |
| default options are |
| |
| </p> |
| <pre><code>{ encoding: 'utf8', |
| timeout: 0, |
| maxBuffer: 200*1024, |
| killSignal: 'SIGTERM', |
| cwd: null, |
| env: null }</code></pre> |
| <p>If <code>timeout</code> is greater than 0, then it will kill the child process |
| if it runs longer than <code>timeout</code> milliseconds. The child process is killed with |
| <code>killSignal</code> (default: <code>'SIGTERM'</code>). <code>maxBuffer</code> specifies the largest |
| amount of data allowed on stdout or stderr - if this value is exceeded then |
| the child process is killed. |
| |
| |
| </p> |
| <h2>child_process.execFile(file, args, options, callback)<span><a class="mark" href="#child_process_child_process_execfile_file_args_options_callback" id="child_process_child_process_execfile_file_args_options_callback">#</a></span></h2> |
| <div class="signature"><ul> |
| <li><code>file</code> <span class="type">String</span> The filename of the program to run</li> |
| <li><code>args</code> <span class="type">Array</span> List of string arguments</li> |
| <li><code>options</code> <span class="type">Object</span><ul> |
| <li><code>cwd</code> <span class="type">String</span> Current working directory of the child process</li> |
| <li><code>env</code> <span class="type">Object</span> Environment key-value pairs</li> |
| <li><code>encoding</code> <span class="type">String</span> (Default: 'utf8')</li> |
| <li><code>timeout</code> <span class="type">Number</span> (Default: 0)</li> |
| <li><code>maxBuffer</code> <span class="type">Number</span> (Default: 200*1024)</li> |
| <li><code>killSignal</code> <span class="type">String</span> (Default: 'SIGTERM')</li> |
| </ul> |
| </li> |
| <li><code>callback</code> <span class="type">Function</span> called with the output when process terminates<ul> |
| <li><code>error</code> <span class="type">Error</span></li> |
| <li><code>stdout</code> <span class="type">Buffer</span></li> |
| <li><code>stderr</code> <span class="type">Buffer</span></li> |
| </ul> |
| </li> |
| <li>Return: ChildProcess object</li> |
| </div></ul> |
| <p>This is similar to <code>child_process.exec()</code> except it does not execute a |
| subshell but rather the specified file directly. This makes it slightly |
| leaner than <code>child_process.exec</code>. It has the same options. |
| |
| |
| </p> |
| <h2>child_process.fork(modulePath, [args], [options])<span><a class="mark" href="#child_process_child_process_fork_modulepath_args_options" id="child_process_child_process_fork_modulepath_args_options">#</a></span></h2> |
| <div class="signature"><ul> |
| <li><code>modulePath</code> <span class="type">String</span> The module to run in the child</li> |
| <li><code>args</code> <span class="type">Array</span> List of string arguments</li> |
| <li><code>options</code> <span class="type">Object</span><ul> |
| <li><code>cwd</code> <span class="type">String</span> Current working directory of the child process</li> |
| <li><code>env</code> <span class="type">Object</span> Environment key-value pairs</li> |
| <li><code>encoding</code> <span class="type">String</span> (Default: 'utf8')</li> |
| <li><code>execPath</code> <span class="type">String</span> Executable used to create the child process</li> |
| <li><code>execArgv</code> <span class="type">Array</span> List of string arguments passed to the executable |
| (Default: <code>process.execArgv</code>)</li> |
| <li><code>silent</code> <span class="type">Boolean</span> If true, prevent stdout and stderr in the spawned node |
| process from being associated with the parent's (default is false)</li> |
| </ul> |
| </li> |
| <li>Return: ChildProcess object</li> |
| </div></ul> |
| <p>This is a special case of the <code>spawn()</code> functionality for spawning Node |
| processes. In addition to having all the methods in a normal ChildProcess |
| instance, the returned object has a communication channel built-in. See |
| <code>child.send(message, [sendHandle])</code> for details. |
| |
| </p> |
| <p>These child Nodes are still whole new instances of V8. Assume at least 30ms |
| startup and 10mb memory for each new Node. That is, you cannot create many |
| thousands of them. |
| |
| </p> |
| <p>The <code>execPath</code> property in the <code>options</code> object allows for a process to be |
| created for the child rather than the current <code>node</code> executable. This should be |
| done with care and by default will talk over the fd represented an |
| environmental variable <code>NODE_CHANNEL_FD</code> on the child process. The input and |
| output on this fd is expected to be line delimited JSON objects. |
| |
| </p> |
| |
| </div> |
| </div> |
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