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368 lines
8.7 KiB
Markdown
368 lines
8.7 KiB
Markdown
# process
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<!-- type=global -->
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The `process` object is a global object and can be accessed from anywhere.
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It is an instance of `EventEmitter`.
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## Event: 'exit'
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`function () {}`
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Emitted when the process is about to exit. This is a good hook to perform
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constant time checks of the module's state (like for unit tests). The main
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event loop will no longer be run after the 'exit' callback finishes, so
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timers may not be scheduled.
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Example of listening for `exit`:
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process.on('exit', function () {
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process.nextTick(function () {
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console.log('This will not run');
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});
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console.log('About to exit.');
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});
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## Event: 'uncaughtException'
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`function (err) { }`
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Emitted when an exception bubbles all the way back to the event loop. If a
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listener is added for this exception, the default action (which is to print
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a stack trace and exit) will not occur.
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Example of listening for `uncaughtException`:
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process.on('uncaughtException', function (err) {
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console.log('Caught exception: ' + err);
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});
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setTimeout(function () {
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console.log('This will still run.');
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}, 500);
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// Intentionally cause an exception, but don't catch it.
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nonexistentFunc();
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console.log('This will not run.');
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Note that `uncaughtException` is a very crude mechanism for exception
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handling. Using try / catch in your program will give you more control over
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your program's flow. Especially for server programs that are designed to
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stay running forever, `uncaughtException` can be a useful safety mechanism.
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## Signal Events
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<!--type=event-->
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<!--name=SIGINT, SIGUSR1, etc.-->
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`function () {}`
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Emitted when the processes receives a signal. See sigaction(2) for a list of
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standard POSIX signal names such as SIGINT, SIGUSR1, etc.
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Example of listening for `SIGINT`:
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// Start reading from stdin so we don't exit.
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process.stdin.resume();
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process.on('SIGINT', function () {
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console.log('Got SIGINT. Press Control-D to exit.');
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});
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An easy way to send the `SIGINT` signal is with `Control-C` in most terminal
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programs.
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## process.stdout
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A `Writable Stream` to `stdout`.
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Example: the definition of `console.log`
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console.log = function (d) {
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process.stdout.write(d + '\n');
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};
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`process.stderr` and `process.stdout` are unlike other streams in Node in
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that writes to them are usually blocking. They are blocking in the case
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that they refer to regular files or TTY file descriptors. In the case they
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refer to pipes, they are non-blocking like other streams.
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## process.stderr
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A writable stream to stderr.
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`process.stderr` and `process.stdout` are unlike other streams in Node in
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that writes to them are usually blocking. They are blocking in the case
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that they refer to regular files or TTY file descriptors. In the case they
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refer to pipes, they are non-blocking like other streams.
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## process.stdin
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A `Readable Stream` for stdin. The stdin stream is paused by default, so one
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must call `process.stdin.resume()` to read from it.
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Example of opening standard input and listening for both events:
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process.stdin.resume();
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process.stdin.setEncoding('utf8');
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process.stdin.on('data', function (chunk) {
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process.stdout.write('data: ' + chunk);
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});
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process.stdin.on('end', function () {
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process.stdout.write('end');
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});
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## process.argv
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An array containing the command line arguments. The first element will be
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'node', the second element will be the name of the JavaScript file. The
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next elements will be any additional command line arguments.
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// print process.argv
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process.argv.forEach(function (val, index, array) {
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console.log(index + ': ' + val);
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});
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This will generate:
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$ node process-2.js one two=three four
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0: node
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1: /Users/mjr/work/node/process-2.js
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2: one
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3: two=three
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4: four
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## process.execPath
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This is the absolute pathname of the executable that started the process.
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Example:
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/usr/local/bin/node
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## process.abort()
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This causes node to emit an abort. This will cause node to exit and
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generate a core file.
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## process.chdir(directory)
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Changes the current working directory of the process or throws an exception if that fails.
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console.log('Starting directory: ' + process.cwd());
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try {
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process.chdir('/tmp');
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console.log('New directory: ' + process.cwd());
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}
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catch (err) {
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console.log('chdir: ' + err);
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}
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## process.cwd()
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Returns the current working directory of the process.
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console.log('Current directory: ' + process.cwd());
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## process.env
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An object containing the user environment. See environ(7).
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## process.exit([code])
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Ends the process with the specified `code`. If omitted, exit uses the
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'success' code `0`.
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To exit with a 'failure' code:
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process.exit(1);
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The shell that executed node should see the exit code as 1.
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## process.getgid()
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Gets the group identity of the process. (See getgid(2).)
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This is the numerical group id, not the group name.
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console.log('Current gid: ' + process.getgid());
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## process.setgid(id)
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Sets the group identity of the process. (See setgid(2).) This accepts either
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a numerical ID or a groupname string. If a groupname is specified, this method
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blocks while resolving it to a numerical ID.
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console.log('Current gid: ' + process.getgid());
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try {
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process.setgid(501);
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console.log('New gid: ' + process.getgid());
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}
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catch (err) {
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console.log('Failed to set gid: ' + err);
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}
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## process.getuid()
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Gets the user identity of the process. (See getuid(2).)
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This is the numerical userid, not the username.
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console.log('Current uid: ' + process.getuid());
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## process.setuid(id)
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Sets the user identity of the process. (See setuid(2).) This accepts either
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a numerical ID or a username string. If a username is specified, this method
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blocks while resolving it to a numerical ID.
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console.log('Current uid: ' + process.getuid());
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try {
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process.setuid(501);
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console.log('New uid: ' + process.getuid());
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}
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catch (err) {
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console.log('Failed to set uid: ' + err);
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}
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## process.version
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A compiled-in property that exposes `NODE_VERSION`.
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console.log('Version: ' + process.version);
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## process.versions
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A property exposing version strings of node and its dependencies.
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console.log(process.versions);
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Will output:
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{ node: '0.4.12',
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v8: '3.1.8.26',
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ares: '1.7.4',
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ev: '4.4',
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openssl: '1.0.0e-fips' }
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## process.installPrefix
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A compiled-in property that exposes `NODE_PREFIX`.
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console.log('Prefix: ' + process.installPrefix);
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## process.kill(pid, [signal])
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Send a signal to a process. `pid` is the process id and `signal` is the
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string describing the signal to send. Signal names are strings like
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'SIGINT' or 'SIGUSR1'. If omitted, the signal will be 'SIGTERM'.
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See kill(2) for more information.
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Note that just because the name of this function is `process.kill`, it is
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really just a signal sender, like the `kill` system call. The signal sent
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may do something other than kill the target process.
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Example of sending a signal to yourself:
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process.on('SIGHUP', function () {
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console.log('Got SIGHUP signal.');
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});
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setTimeout(function () {
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console.log('Exiting.');
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process.exit(0);
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}, 100);
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process.kill(process.pid, 'SIGHUP');
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## process.pid
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The PID of the process.
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console.log('This process is pid ' + process.pid);
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## process.title
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Getter/setter to set what is displayed in 'ps'.
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## process.arch
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What processor architecture you're running on: `'arm'`, `'ia32'`, or `'x64'`.
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console.log('This processor architecture is ' + process.arch);
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## process.platform
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What platform you're running on. `'linux2'`, `'darwin'`, etc.
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console.log('This platform is ' + process.platform);
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## process.memoryUsage()
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Returns an object describing the memory usage of the Node process
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measured in bytes.
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var util = require('util');
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console.log(util.inspect(process.memoryUsage()));
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This will generate:
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{ rss: 4935680,
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heapTotal: 1826816,
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heapUsed: 650472 }
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`heapTotal` and `heapUsed` refer to V8's memory usage.
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## process.nextTick(callback)
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On the next loop around the event loop call this callback.
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This is *not* a simple alias to `setTimeout(fn, 0)`, it's much more
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efficient.
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process.nextTick(function () {
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console.log('nextTick callback');
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});
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## process.umask([mask])
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Sets or reads the process's file mode creation mask. Child processes inherit
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the mask from the parent process. Returns the old mask if `mask` argument is
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given, otherwise returns the current mask.
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var oldmask, newmask = 0644;
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oldmask = process.umask(newmask);
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console.log('Changed umask from: ' + oldmask.toString(8) +
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' to ' + newmask.toString(8));
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## process.uptime()
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Number of seconds Node has been running.
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