node/doc/api/cli.md

Command Line Options

Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.

To view this documentation as a manual page in a terminal, run man node.

Synopsis

node [options] [v8 options] [script.js | -e "script" | -] [--] [arguments]

node debug [script.js | -e "script" | <host>:<port>] …

node --v8-options

Execute without arguments to start the REPL.

For more info about node debug, please see the debugger documentation.

Options

-v, --version

Print node's version.

-h, --help

Print node command line options. The output of this option is less detailed than this document.

-e, --eval "script"

Evaluate the following argument as JavaScript. The modules which are predefined in the REPL can also be used in script.

Note: On Windows, using cmd.exe a single quote will not work correctly because it only recognizes double " for quoting. In Powershell or Git bash, both ' and " are usable.

-p, --print "script"

Identical to -e but prints the result.

-c, --check

Syntax check the script without executing.

-i, --interactive

Opens the REPL even if stdin does not appear to be a terminal.

-r, --require module

Preload the specified module at startup.

Follows require()'s module resolution rules. module may be either a path to a file, or a node module name.

--inspect[=[host:]port]

Activate inspector on host:port. Default is 127.0.0.1:9229.

V8 inspector integration allows tools such as Chrome DevTools and IDEs to debug and profile Node.js instances. The tools attach to Node.js instances via a tcp port and communicate using the Chrome Debugging Protocol.

--inspect-brk[=[host:]port]

Activate inspector on host:port and break at start of user script. Default host:port is 127.0.0.1:9229.

--inspect-port=[host:]port

Set the host:port to be used when the inspector is activated. Useful when activating the inspector by sending the SIGUSR1 signal.

Default host is 127.0.0.1.

--no-deprecation

Silence deprecation warnings.

--trace-deprecation

Print stack traces for deprecations.

--throw-deprecation

Throw errors for deprecations.

--pending-deprecation

Emit pending deprecation warnings.

Note: Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the --pending-deprecation command line flag, or the NODE_PENDING_DEPRECATION=1 environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.

--no-warnings

Silence all process warnings (including deprecations).

--abort-on-uncaught-exception

Aborting instead of exiting causes a core file to be generated for post-mortem analysis using a debugger (such as lldb, gdb, and mdb).

--trace-warnings

Print stack traces for process warnings (including deprecations).

--redirect-warnings=file

Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead.

--trace-sync-io

Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.

--trace-events-enabled

Enables the collection of trace event tracing information.

--trace-event-categories

A comma separated list of categories that should be traced when trace event tracing is enabled using --trace-events-enabled.

--zero-fill-buffers

Automatically zero-fills all newly allocated Buffer and SlowBuffer instances.

--preserve-symlinks

Instructs the module loader to preserve symbolic links when resolving and caching modules.

By default, when Node.js loads a module from a path that is symbolically linked to a different on-disk location, Node.js will dereference the link and use the actual on-disk "real path" of the module as both an identifier and as a root path to locate other dependency modules. In most cases, this default behavior is acceptable. However, when using symbolically linked peer dependencies, as illustrated in the example below, the default behavior causes an exception to be thrown if moduleA attempts to require moduleB as a peer dependency:

{appDir}
 ├── app
 │   ├── index.js
 │   └── node_modules
 │       ├── moduleA -> {appDir}/moduleA
 │       └── moduleB
 │           ├── index.js
 │           └── package.json
 └── moduleA
     ├── index.js
     └── package.json

The --preserve-symlinks command line flag instructs Node.js to use the symlink path for modules as opposed to the real path, allowing symbolically linked peer dependencies to be found.

Note, however, that using --preserve-symlinks can have other side effects. Specifically, symbolically linked native modules can fail to load if those are linked from more than one location in the dependency tree (Node.js would see those as two separate modules and would attempt to load the module multiple times, causing an exception to be thrown).

--track-heap-objects

Track heap object allocations for heap snapshots.

--prof-process

Process v8 profiler output generated using the v8 option --prof.

--v8-options

Print v8 command line options.

Note: V8 options allow words to be separated by both dashes (-) or underscores (_).

For example, --stack-trace-limit is equivalent to --stack_trace_limit.

--tls-cipher-list=list

Specify an alternative default TLS cipher list. (Requires Node.js to be built with crypto support. (Default))

--enable-fips

Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with ./configure --openssl-fips)

--force-fips

Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.) (Same requirements as --enable-fips)

--openssl-config=file

Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with ./configure --openssl-fips.

--use-openssl-ca, --use-bundled-ca

Use OpenSSL's default CA store or use bundled Mozilla CA store as supplied by current Node.js version. The default store is selectable at build-time.

Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environment variables.

The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.

See SSL_CERT_DIR and SSL_CERT_FILE.

--icu-data-dir=file

Specify ICU data load path. (overrides NODE_ICU_DATA)

-

Alias for stdin, analogous to the use of - in other command line utilities, meaning that the script will be read from stdin, and the rest of the options are passed to that script.

--

Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument will be used as a script filename.

Environment Variables

NODE_DEBUG=module[,…]

','-separated list of core modules that should print debug information.

NODE_PATH=path[:…]

':'-separated list of directories prefixed to the module search path.

Note: On Windows, this is a ';'-separated list instead.

NODE_DISABLE_COLORS=1

When set to 1 colors will not be used in the REPL.

NODE_ICU_DATA=file

Data path for ICU (Intl object) data. Will extend linked-in data when compiled with small-icu support.

NODE_NO_WARNINGS=1

When set to 1, process warnings are silenced.

NODE_OPTIONS=options...

A space-separated list of command line options. options... are interpreted as if they had been specified on the command line before the actual command line (so they can be overridden). Node will exit with an error if an option that is not allowed in the environment is used, such as -p or a script file.

Node options that are allowed are:

• --enable-fips
• --force-fips
• --icu-data-dir
• --inspect-brk
• --inspect-port
• --inspect
• --no-deprecation
• --no-warnings
• --openssl-config
• --redirect-warnings
• --require, -r
• --throw-deprecation
• --tls-cipher-list
• --trace-deprecation
• --trace-events-categories
• --trace-events-enabled
• --trace-sync-io
• --trace-warnings
• --track-heap-objects
• --use-bundled-ca
• --use-openssl-ca
• --v8-pool-size
• --zero-fill-buffers

V8 options that are allowed are:

• --abort-on-uncaught-exception
• --max-old-space-size

NODE_PENDING_DEPRECATION=1

When set to 1, emit pending deprecation warnings.

Note: Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the --pending-deprecation command line flag, or the NODE_PENDING_DEPRECATION=1 environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.

NODE_PRESERVE_SYMLINKS=1

When set to 1, instructs the module loader to preserve symbolic links when resolving and caching modules.

NODE_REPL_HISTORY=file

Path to the file used to store the persistent REPL history. The default path is ~/.node_repl_history, which is overridden by this variable. Setting the value to an empty string ("" or " ") disables persistent REPL history.

NODE_EXTRA_CA_CERTS=file

When set, the well known "root" CAs (like VeriSign) will be extended with the extra certificates in file. The file should consist of one or more trusted certificates in PEM format. A message will be emitted (once) with process.emitWarning() if the file is missing or malformed, but any errors are otherwise ignored.

Note that neither the well known nor extra certificates are used when the ca options property is explicitly specified for a TLS or HTTPS client or server.

OPENSSL_CONF=file

Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with ./configure --openssl-fips.

If the --openssl-config command line option is used, the environment variable is ignored.

SSL_CERT_DIR=dir

If --use-openssl-ca is enabled, this overrides and sets OpenSSL's directory containing trusted certificates.

Note: Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

SSL_CERT_FILE=file

If --use-openssl-ca is enabled, this overrides and sets OpenSSL's file containing trusted certificates.

Note: Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

NODE_REDIRECT_WARNINGS=file

When set, process warnings will be emitted to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead. This is equivalent to using the --redirect-warnings=file command-line flag.

UV_THREADPOOL_SIZE=size

Set the number of threads used in libuv's threadpool to size threads.

Asynchronous system APIs are used by Node.js whenever possible, but where they do not exist, libuv's threadpool is used to create asynchronous node APIs based on synchronous system APIs. Node.js APIs that use the threadpool are:

• all fs APIs, other than the file watcher APIs and those that are explicitly synchronous
• crypto.pbkdf2()
• crypto.randomBytes(), unless it is used without a callback
• crypto.randomFill()
• dns.lookup()
• all zlib APIs, other than those that are explicitly synchronous

Because libuv's threadpool has a fixed size, it means that if for whatever reason any of these APIs takes a long time, other (seemingly unrelated) APIs that run in libuv's threadpool will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv's threadpool by setting the 'UV_THREADPOOL_SIZE' environment variable to a value greater than 4 (its current default value). For more information, see the libuv threadpool documentation.