Process execution for humans

^{Sindre's open source work is supported by the community}

^{Special thanks to:}

This package improves child_process methods with:

• Promise interface.
• Scripts interface, like zx.
• Improved Windows support, including shebang binaries.
• Executes locally installed binaries without npx.
• Cleans up child processes when the parent process ends.
• Redirect stdin/stdout/stderr from/to files, streams, iterables, strings, Uint8Array or objects.
• Transform stdin/stdout/stderr with simple functions.
• Iterate over each text line output by the process.
• Fail-safe process termination.
• Get interleaved output from stdout and stderr similar to what is printed on the terminal.
• Strips the final newline from the output so you don't have to do stdout.trim().
• Convenience methods to pipe processes' input and output.
• Can specify file and arguments as a single string without a shell.
• Verbose mode for debugging.
• More descriptive errors.
• Higher max buffer: 100 MB instead of 1 MB.

npm install execa

import {execa} from 'execa';

const {stdout} = await execa('echo', ['unicorns']);
console.log(stdout);
//=> 'unicorns'

For more information about Execa scripts, please see this page.

import {$} from 'execa';

const branch = await $`git branch --show-current`;
await $`dep deploy --branch=${branch}`;

import {$} from 'execa';

const args = ['unicorns', '&', 'rainbows!'];
const {stdout} = await $`echo ${args}`;
console.log(stdout);
//=> 'unicorns & rainbows!'

import {$} from 'execa';

await $({stdio: 'inherit'})`echo unicorns`;
//=> 'unicorns'

import {$} from 'execa';

const $$ = $({stdio: 'inherit'});

await $$`echo unicorns`;
//=> 'unicorns'

await $$`echo rainbows`;
//=> 'rainbows'

> node file.js
unicorns
rainbows

> NODE_DEBUG=execa node file.js
[16:50:03.305] echo unicorns
unicorns
[16:50:03.308] echo rainbows
rainbows

import {execa} from 'execa';

// Similar to `echo unicorns > stdout.txt` in Bash
await execa('echo', ['unicorns']).pipeStdout('stdout.txt');

// Similar to `echo unicorns 2> stdout.txt` in Bash
await execa('echo', ['unicorns']).pipeStderr('stderr.txt');

// Similar to `echo unicorns &> stdout.txt` in Bash
await execa('echo', ['unicorns'], {all: true}).pipeAll('all.txt');

import {execa} from 'execa';

// Similar to `cat < stdin.txt` in Bash
const {stdout} = await execa('cat', {inputFile: 'stdin.txt'});
console.log(stdout);
//=> 'unicorns'

import {execa} from 'execa';

const {stdout} = await execa('echo', ['unicorns']).pipeStdout(process.stdout);
// Prints `unicorns`
console.log(stdout);
// Also returns 'unicorns'

import {execa} from 'execa';

// Similar to `echo unicorns | cat` in Bash
const {stdout} = await execa('echo', ['unicorns']).pipeStdout(execa('cat'));
console.log(stdout);
//=> 'unicorns'

import {execa} from 'execa';

// Catching an error
try {
	await execa('unknown', ['command']);
} catch (error) {
	console.log(error);
	/*
	{
		message: 'Command failed with ENOENT: unknown command spawn unknown ENOENT',
		errno: -2,
		code: 'ENOENT',
		syscall: 'spawn unknown',
		path: 'unknown',
		spawnargs: ['command'],
		originalMessage: 'spawn unknown ENOENT',
		shortMessage: 'Command failed with ENOENT: unknown command spawn unknown ENOENT',
		command: 'unknown command',
		escapedCommand: 'unknown command',
		stdout: '',
		stderr: '',
		failed: true,
		timedOut: false,
		isCanceled: false,
		isTerminated: false
	}
	*/
}

Executes a command using file ...arguments. file is a string or a file URL. arguments are an array of strings. Returns a childProcess.

Arguments are automatically escaped. They can contain any character, including spaces.

This is the preferred method when executing single commands.

Executes a Node.js file using node scriptPath ...arguments. file is a string or a file URL. arguments are an array of strings. Returns a childProcess.

Arguments are automatically escaped. They can contain any character, including spaces.

This is the preferred method when executing Node.js files.

Like child_process#fork():

• the current Node version and options are used. This can be overridden using the nodePath and nodeOptions options.
• the shell option cannot be used
• an extra channel ipc is passed to stdio

Executes a command. The command string includes both the file and its arguments. Returns a childProcess.

Arguments are automatically escaped. They can contain any character, but spaces must use ${} like $`echo ${'has space'}`.

This is the preferred method when executing multiple commands in a script file.

The command string can inject any ${value} with the following types: string, number, childProcess or an array of those types. For example: $`echo one ${'two'} ${3} ${['four', 'five']}`. For ${childProcess}, the process's stdout is used.

For more information, please see this section and this page.

Returns a new instance of $ but with different default options. Consecutive calls are merged to previous ones.

This can be used to either:

• Set options for a specific command: $(options)`command`
• Share options for multiple commands: const $$ = $(options); $$`command`; $$`otherCommand`;

Executes a command. The command string includes both the file and its arguments. Returns a childProcess.

Arguments are automatically escaped. They can contain any character, but spaces must be escaped with a backslash like execaCommand('echo has\\ space').

This is the preferred method when executing a user-supplied command string, such as in a REPL.

Same as execa() but synchronous.

Cannot use the following options: all, cleanup, buffer, detached, serialization and signal. Also, the stdin, stdout, stderr, stdio and input options cannot be an array, an iterable or a web stream. Node.js streams must have a file descriptor unless the input option is used.

Returns or throws a childProcessResult.

Same as $`command` but synchronous.

Cannot use the following options: all, cleanup, buffer, detached, serialization and signal. Also, the stdin, stdout, stderr, stdio and input options cannot be an array, an iterable or a web stream. Node.js streams must have a file descriptor unless the input option is used.

Returns or throws a childProcessResult.

Same as execaCommand() but synchronous.

Cannot use the following options: all, cleanup, buffer, detached, serialization and signal. Also, the stdin, stdout, stderr, stdio and input options cannot be an array, an iterable or a web stream. Node.js streams must have a file descriptor unless the input option is used.

Returns or throws a childProcessResult.

For all the methods above, no shell interpreter (Bash, cmd.exe, etc.) is used unless the shell option is set. This means shell-specific characters and expressions ($variable, &&, ||, ;, |, etc.) have no special meaning and do not need to be escaped.

The return value of all asynchronous methods is both:

• a Promise resolving or rejecting with a childProcessResult.
• a child_process instance with the following additional methods and properties.

Type: ReadableStream | undefined

Stream combining/interleaving stdout and stderr.

This is undefined if either:

• the all option is false (the default value)
• both stdout and stderr options are set to 'inherit', 'ipc', 'ignore', Stream or integer

Pipe the child process's stdout to target, which can be:

• Another execa() return value
• A writable stream
• A file path string

If the target is another execa() return value, it is returned. Otherwise, the original execa() return value is returned. This allows chaining pipeStdout() then awaiting the final result.

The stdout option must be kept as pipe, its default value.

Like pipeStdout() but piping the child process's stderr instead.

The stderr option must be kept as pipe, its default value.

Combines both pipeStdout() and pipeStderr().

Either the stdout option or the stderr option must be kept as pipe, their default value. Also, the all option must be set to true.

Type: object

Result of a child process execution. On success this is a plain object. On failure this is also an Error instance.

The child process fails when:

• its exit code is not 0
• it was terminated with a signal
• timing out
• being canceled
• there's not enough memory or there are already too many child processes

Type: string

The file and arguments that were run, for logging purposes.

This is not escaped and should not be executed directly as a process, including using execa() or execaCommand().

Type: string

Same as command but escaped.

This is meant to be copy and pasted into a shell, for debugging purposes. Since the escaping is fairly basic, this should not be executed directly as a process, including using execa() or execaCommand().

Type: number | undefined

The numeric exit code of the process that was run.

This is undefined when the process could not be spawned or was terminated by a signal.

Type: string | Uint8Array | unknown[] | undefined

The output of the process on stdout.

This is undefined if the stdout option is set to 'inherit', 'ipc', 'ignore', Stream or integer. This is an array if the stdout option is a transform in object mode.

Type: string | Uint8Array | unknown[] | undefined

The output of the process on stderr.

This is undefined if the stderr option is set to 'inherit', 'ipc', 'ignore', Stream or integer. This is an array if the stderr option is a transform in object mode.

Type: string | Uint8Array | unknown[] | undefined

The output of the process with stdout and stderr interleaved.

This is undefined if either:

• the all option is false (the default value)
• both stdout and stderr options are set to 'inherit', 'ipc', 'ignore', Stream or integer

This is an array if either the stdout or stderr option is a transform in object mode.

Type: Array<string | Uint8Array | unknown[] | undefined>

The output of the process on stdin, stdout, stderr and other file descriptors.

Items are undefined when their corresponding stdio option is set to 'inherit', 'ipc', 'ignore', Stream or integer. Items are arrays when their corresponding stdio option is a transform in object mode.

Type: boolean

Whether the process failed to run.

Type: boolean

Whether the process timed out.

Type: boolean

Whether the process was canceled using the signal option.

Type: boolean

Whether the process was terminated by a signal (like SIGTERM) sent by either:

• The current process.
• Another process. This case is not supported on Windows.

Type: string | undefined

The name of the signal (like SIGTERM) that terminated the process, sent by either:

• The current process.
• Another process. This case is not supported on Windows.

If a signal terminated the process, this property is defined and included in the error message. Otherwise it is undefined.

Type: string | undefined

A human-friendly description of the signal that was used to terminate the process. For example, Floating point arithmetic error.

If a signal terminated the process, this property is defined and included in the error message. Otherwise it is undefined. It is also undefined when the signal is very uncommon which should seldomly happen.

Type: string

The cwd of the command if provided in the command options. Otherwise it is process.cwd().

Type: string

Error message when the child process failed to run. In addition to the underlying error message, it also contains some information related to why the child process errored.

The child process stderr, stdout and other file descriptors' output are appended to the end, separated with newlines and not interleaved.

Type: string

This is the same as the message property except it does not include the child process stdout/stderr/stdio.

Type: string | undefined

Original error message. This is the same as the message property excluding the child process stdout/stderr/stdio and some additional information added by Execa.

This is undefined unless the child process exited due to an error event or a timeout.

Type: object

Type: boolean
Default: true

Kill the spawned process when the parent process exits unless either: - the spawned process is detached - the parent process is terminated abruptly, for example, with SIGKILL as opposed to SIGTERM or a normal exit

Type: boolean
Default: true with $, false otherwise

Prefer locally installed binaries when looking for a binary to execute.
If you $ npm install foo, you can then execa('foo').

Type: string | URL
Default: process.cwd()

Preferred path to find locally installed binaries in (use with preferLocal).

Type: string | URL
Default: process.execPath (Current Node.js executable)

Path to the Node.js executable to use in child processes.

This can be either an absolute path or a path relative to the cwd option.

Requires preferLocal to be true.

For example, this can be used together with get-node to run a specific Node.js version in a child process.

Type: boolean
Default: true

Buffer the output from the spawned process. When set to false, you must read the output of stdout and stderr (or all if the all option is true). Otherwise the returned promise will not be resolved/rejected.

If the spawned process fails, error.stdout, error.stderr, error.all and error.stdio will contain the buffered data.

Type: string | Uint8Array | stream.Readable

Write some input to the child process' stdin.

See also the inputFile and stdin options.

Type: string | URL

Use a file as input to the child process' stdin.

See also the input and stdin options.

Type: string | number | stream.Readable | ReadableStream | URL | Uint8Array | Iterable<string | Uint8Array> | AsyncIterable<string | Uint8Array> | AsyncGeneratorFunction<string | Uint8Array> (or a tuple of those types)
Default: inherit with $, pipe otherwise

How to setup the child process' standard input. This can be:

• 'pipe': Sets childProcess.stdin stream.
• 'overlapped': Like 'pipe' but asynchronous on Windows.
• 'ignore': Do not use stdin.
• 'ipc': Sets an IPC channel. You can also use execaNode() instead.
• 'inherit': Re-use the current process' stdin.
• an integer: Re-use a specific file descriptor from the current process.
• a Node.js Readable stream.
• { file: 'path' } object.
• a file URL.
• a web ReadableStream.
• an Iterable or an AsyncIterable
• an Uint8Array.

This can be an array of values such as ['inherit', 'pipe'] or [filePath, 'pipe'].

This can also be an async generator function to transform the input. Learn more.

Type: string | number | stream.Writable | WritableStream | URL | AsyncGeneratorFunction<string | Uint8Array> (or a tuple of those types)
Default: pipe

How to setup the child process' standard output. This can be:

• 'pipe': Sets childProcessResult.stdout (as a string or Uint8Array) and childProcess.stdout (as a stream).
• 'overlapped': Like 'pipe' but asynchronous on Windows.
• 'ignore': Do not use stdout.
• 'ipc': Sets an IPC channel. You can also use execaNode() instead.
• 'inherit': Re-use the current process' stdout.
• an integer: Re-use a specific file descriptor from the current process.
• a Node.js Writable stream.
• { file: 'path' } object.
• a file URL.
• a web WritableStream.

This can be an array of values such as ['inherit', 'pipe'] or [filePath, 'pipe'].

This can also be an async generator function to transform the output. Learn more.

Type: string | number | stream.Writable | WritableStream | URL | AsyncGeneratorFunction<string | Uint8Array> (or a tuple of those types)\ Default: pipe`

How to setup the child process' standard error. This can be:

• 'pipe': Sets childProcessResult.stderr (as a string or Uint8Array) and childProcess.stderr (as a stream).
• 'overlapped': Like 'pipe' but asynchronous on Windows.
• 'ignore': Do not use stderr.
• 'ipc': Sets an IPC channel. You can also use execaNode() instead.
• 'inherit': Re-use the current process' stderr.
• an integer: Re-use a specific file descriptor from the current process.
• a Node.js Writable stream.
• { file: 'path' } object.
• a file URL.
• a web WritableStream.

This can be an array of values such as ['inherit', 'pipe'] or [filePath, 'pipe'].

This can also be an async generator function to transform the output. Learn more.

Type: string | Array<string | number | stream.Readable | stream.Writable | ReadableStream | WritableStream | URL | Uint8Array | Iterable<string | Uint8Array> | AsyncIterable<string | Uint8Array> | AsyncGeneratorFunction<string | Uint8Array>> (or a tuple of those types)
Default: pipe

Like the stdin, stdout and stderr options but for all file descriptors at once. For example, {stdio: ['ignore', 'pipe', 'pipe']} is the same as {stdin: 'ignore', stdout: 'pipe', stderr: 'pipe'}.

A single string can be used as a shortcut. For example, {stdio: 'pipe'} is the same as {stdin: 'pipe', stdout: 'pipe', stderr: 'pipe'}.

The array can have more than 3 items, to create additional file descriptors beyond stdin/stdout/stderr. For example, {stdio: ['pipe', 'pipe', 'pipe', 'ipc']} sets a fourth file descriptor 'ipc'.

Type: boolean
Default: false

Add an .all property on the promise and the resolved value. The property contains the output of the process with stdout and stderr interleaved.

Type: boolean
Default: true

Setting this to false resolves the promise with the error instead of rejecting it.

Type: boolean
Default: true

Strip the final newline character from the output.

Type: boolean
Default: true

If true, the child process uses both the env option and the current process' environment variables (process.env). If false, only the env option is used, not process.env.

Execa also accepts the below options which are the same as the options for child_process#spawn()/child_process#exec()

Type: string | URL
Default: process.cwd()

Current working directory of the child process.

Type: object
Default: process.env

Environment key-value pairs.

Unless the extendEnv option is false, the child process also uses the current process' environment variables (process.env).

Type: string

Explicitly set the value of argv[0] sent to the child process. This will be set to file if not specified.

Type: string
Default: 'json'

Specify the kind of serialization used for sending messages between processes when using the stdio: 'ipc' option or execaNode(): - json: Uses JSON.stringify() and JSON.parse(). - advanced: Uses v8.serialize()

More info.

Type: boolean

Prepare child to run independently of its parent process. Specific behavior depends on the platform.

Type: number

Sets the user identity of the process.

Type: number

Sets the group identity of the process.

Type: boolean | string | URL
Default: false

If true, runs file inside of a shell. Uses /bin/sh on UNIX and cmd.exe on Windows. A different shell can be specified as a string. The shell should understand the -c switch on UNIX or /d /s /c on Windows.

We recommend against using this option since it is:

• not cross-platform, encouraging shell-specific syntax.
• slower, because of the additional shell interpretation.
• unsafe, potentially allowing command injection.

Type: string
Default: utf8

Specify the character encoding used to decode the stdout, stderr and stdio output. If set to 'buffer', then stdout, stderr and stdio will be Uint8Arrays instead of strings.

Type: number
Default: 0

If timeout`` is greater than 0`, the child process will be terminated if it runs for longer than that amount of milliseconds.

Type: number
Default: 100_000_000 (100 MB)

Largest amount of data in bytes allowed on stdout, stderr and stdio.

Type: string | number
Default: SIGTERM

Signal used to terminate the child process when:

• using the signal, timeout, maxBuffer or cleanup option
• calling subprocess.kill() with no arguments

This can be either a name (like "SIGTERM") or a number (like 9).

Type: number | false
Default: 5000

If the child process is terminated but does not exit, forcefully exit it by sending SIGKILL.

The grace period is 5 seconds by default. This feature can be disabled with false.

This works when the child process is terminated by either:

• the signal, timeout, maxBuffer or cleanup option
• calling subprocess.kill() with no arguments

This does not work when the child process is terminated by either:

• calling subprocess.kill() with an argument
• calling process.kill(subprocess.pid)
• sending a termination signal from another process

Also, this does not work on Windows, because Windows doesn't support signals: SIGKILL and SIGTERM both terminate the process immediately. Other packages (such as taskkill) can be used to achieve fail-safe termination on Windows.

Type: AbortSignal

You can abort the spawned process using AbortController.

When AbortController.abort() is called, .isCanceled becomes true.

Type: boolean
Default: false

If true, no quoting or escaping of arguments is done on Windows. Ignored on other platforms. This is set to true automatically when the shell option is true.

Type: boolean
Default: true

On Windows, do not create a new console window. Please note this also prevents CTRL-C from working on Windows.

Type: boolean
Default: false

Print each command on stderr before executing it.

This can also be enabled by setting the NODE_DEBUG=execa environment variable in the current process.

Type: string | URL
Default: process.execPath

Node.js executable used to create the child process.

Type: string[]
Default: process.execArgv

List of CLI options passed to the Node.js executable.

The stdin, stdout and stderr options can be an array of values. The following example redirects stdout to both the terminal and an output.txt file, while also retrieving its value programmatically.

const {stdout} = await execa('npm', ['install'], {stdout: ['inherit', './output.txt', 'pipe']});
console.log(stdout);

When combining inherit with other values, please note that the child process will not be an interactive TTY, even if the parent process is one.

When passing a Node.js stream to the stdin, stdout or stderr option, Node.js requires that stream to have an underlying file or socket, such as the streams created by the fs, net or http core modules. Otherwise the following error is thrown.

TypeError [ERR_INVALID_ARG_VALUE]: The argument 'stdio' is invalid.

This limitation can be worked around by passing either:

• a web stream (ReadableStream or WritableStream)
• [nodeStream, 'pipe'] instead of nodeStream

- await execa(..., {stdout: nodeStream});
+ await execa(..., {stdout: [nodeStream, 'pipe']});

Safely handle failures by using automatic retries and exponential backoff with the p-retry package:

import pRetry from 'p-retry';

const run = async () => {
	const results = await execa('curl', ['-sSL', 'https://sindresorhus.com/unicorn']);
	return results;
};

console.log(await pRetry(run, {retries: 5}));

import {execa} from 'execa';

const abortController = new AbortController();
const subprocess = execa('node', [], {signal: abortController.signal});

setTimeout(() => {
	abortController.abort();
}, 1000);

try {
	await subprocess;
} catch (error) {
	console.log(error.isTerminated); // true
	console.log(error.isCanceled); // true
}

Execa can be combined with get-bin-path to test the current package's binary. As opposed to hard-coding the path to the binary, this validates that the package.json bin field is correctly set up.

import {getBinPath} from 'get-bin-path';

const binPath = await getBinPath();
await execa(binPath);

The all stream and string/Uint8Array properties are guaranteed to interleave stdout and stderr.

However, for performance reasons, the child process might buffer and merge multiple simultaneous writes to stdout or stderr. This prevents proper interleaving.

For example, this prints 1 3 2 instead of 1 2 3 because both console.log() are merged into a single write.

import {execa} from 'execa';

const {all} = await execa('node', ['example.js'], {all: true});
console.log(all);

// example.js
console.log('1'); // writes to stdout
console.error('2'); // writes to stderr
console.log('3'); // writes to stdout

This can be worked around by using setTimeout().

import {setTimeout} from 'timers/promises';

console.log('1');
console.error('2');
await setTimeout(0);
console.log('3');

• gulp-execa - Gulp plugin for Execa
• nvexeca - Run Execa using any Node.js version

• Sindre Sorhus
• @ehmicky