execa

What is execa?

The execa npm package is a process execution tool that simplifies working with child processes in Node.js. It provides a better user experience than the default child_process module by offering a promise-based API, improved Windows support, and additional convenience options.

What are execa's main functionalities?

Executing a shell command

This feature allows you to execute a shell command and obtain the result. The example shows how to execute the 'echo' command and print 'unicorns' to the console.

const execa = require('execa');

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

Running a command synchronously

This feature is used to execute a command synchronously, blocking the event loop until the process has finished. The example synchronously executes the 'echo' command and logs the result.

const execa = require('execa');

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

Handling errors

This feature demonstrates error handling when a command fails to execute. The example attempts to run a non-existent command and catches the error.

const execa = require('execa');

(async () => {
  try {
    const { stdout } = await execa('wrong-command');
    console.log(stdout);
  } catch (error) {
    console.error('Error occurred:', error);
  }
})();

Streaming output

This feature allows you to stream the output of a command directly to the console or another stream. The example streams the output of the 'echo' command to the process's stdout.

const execa = require('execa');

const subprocess = execa('echo', ['unicorns']);
subprocess.stdout.pipe(process.stdout);

Other packages similar to execa

shelljs

ShellJS is a portable Unix shell commands implementation for Node.js. It offers a higher-level API for executing commands but does not support returning promises natively.

cross-spawn

Cross-spawn is a cross-platform solution for spawning child processes. It aims to solve compatibility issues on Windows but does not provide a promise-based API.

README

execa

A better child_process

Why

• Promise interface.
• Strips EOF from the output so you don't have to stdout.trim().
• Supports shebang binaries cross-platform.
• Improved Windows support.
• Higher max buffer. 10 MB instead of 200 KB.
• Executes locally installed binaries by name.
• Cleans up spawned processes when the parent process dies.

Install

$ npm install --save execa

Usage

const execa = require('execa');

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

// pipe the child process stdout to the current stdout
execa('echo', ['unicorns']).stdout.pipe(process.stdout);

execa.shell('echo unicorns').then(result => {
	console.log(result.stdout);
	//=> 'unicorns'
});

// example of catching an error
execa.shell('exit 3').catch(error => {
	console.log(error);
	/*
	{
		message: 'Command failed: /bin/sh -c exit 3'
		killed: false,
		code: 3,
		signal: null,
		cmd: '/bin/sh -c exit 3',
		stdout: '',
		stderr: '',
		timedOut: false
	}
	*/
});

API

execa(file, [arguments], [options])

Execute a file.

Same options as child_process.spawn.

Think of this as a mix of child_process.execFile and child_process.spawn.

Returns a child_process instance, which is enhanced to also be a Promise for a result Object with stdout and stderr properties.

execa.stdout(file, [arguments], [options])

Same as execa(), but returns only stdout.

execa.stderr(file, [arguments], [options])

Same as execa(), but returns only stderr.

execa.shell(command, [options])

Execute a command through the system shell. Prefer execa() whenever possible, as it's both faster and safer.

Same options as child_process.spawn.

Returns a child_process instance.

The child_process instance is enhanced to also be promise for a result object with stdout and stderr properties.

execa.sync(file, [arguments], [options])

Execute a file synchronously.

Same options as child_process.spawnSync, except the default encoding is utf8 instead of buffer.

Returns the same result object as child_process.spawnSync.

This method throws an Error if the command fails.

execa.shellSync(file, [options])

Execute a command synchronously through the system shell.

Same options as child_process.spawnSync, except the default encoding is utf8 instead of buffer.

Returns the same result object as child_process.spawnSync.

options

Additional options:

stripEof

Type: boolean
Default: true

Strip EOF (last newline) from the output.

preferLocal

Type: boolean
Default: true

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

input

Type: string Buffer ReadableStream

Write some input to the stdin of your binary.
Streams are not allowed when using the synchronous methods.

reject

Type: boolean
Default: true

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

cleanup

Type: boolean
Default: true

Keep track of the spawned process and kill it when the parent process exits.

Tips

Save and pipe output from a child process

Let's say you want to show the output of a child process in real-time while also saving it to a variable.

const execa = require('execa');
const getStream = require('get-stream');

const stream = execa('echo', ['foo']).stdout;

stream.pipe(process.stdout);

getStream(stream).then(value => {
	console.log('child output:', value);
});

License

MIT © Sindre Sorhus