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- # execa [](https://travis-ci.org/sindresorhus/execa) [](https://ci.appveyor.com/project/sindresorhus/execa/branch/master) [](https://coveralls.io/github/sindresorhus/execa?branch=master)
- > A better [`child_process`](https://nodejs.org/api/child_process.html)
- ## Why
- - Promise interface.
- - [Strips EOF](https://github.com/sindresorhus/strip-eof) from the output so you don't have to `stdout.trim()`.
- - Supports [shebang](https://en.wikipedia.org/wiki/Shebang_(Unix)) binaries cross-platform.
- - [Improved Windows support.](https://github.com/IndigoUnited/node-cross-spawn#why)
- - Higher max buffer. 10 MB instead of 200 KB.
- - [Executes locally installed binaries by name.](#preferlocal)
- - [Cleans up spawned processes when the parent process dies.](#cleanup)
- ## Install
- ```
- $ npm install execa
- ```
- <a href="https://www.patreon.com/sindresorhus">
- <img src="https://c5.patreon.com/external/logo/become_a_patron_button@2x.png" width="160">
- </a>
- ## Usage
- ```js
- const execa = require('execa');
- (async () => {
- const {stdout} = await execa('echo', ['unicorns']);
- console.log(stdout);
- //=> 'unicorns'
- })();
- ```
- Additional examples:
- ```js
- const execa = require('execa');
- (async () => {
- // Pipe the child process stdout to the current stdout
- execa('echo', ['unicorns']).stdout.pipe(process.stdout);
- // Run a shell command
- const {stdout} = await execa.shell('echo unicorns');
- //=> 'unicorns'
- // Catching an error
- try {
- await 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
- }
- */
- }
- })();
- // Catching an error with a sync method
- try {
- execa.shellSync('exit 3');
- } catch (error) {
- console.log(error);
- /*
- {
- message: 'Command failed: /bin/sh -c exit 3'
- code: 3,
- signal: null,
- cmd: '/bin/sh -c exit 3',
- stdout: '',
- stderr: '',
- timedOut: false
- }
- */
- }
- ```
- ## API
- ### execa(file, [arguments], [options])
- Execute a file.
- Think of this as a mix of `child_process.execFile` and `child_process.spawn`.
- Returns a [`child_process` instance](https://nodejs.org/api/child_process.html#child_process_class_childprocess), 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.
- Returns a [`child_process` instance](https://nodejs.org/api/child_process.html#child_process_class_childprocess).
- 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.
- Returns the same result object as [`child_process.spawnSync`](https://nodejs.org/api/child_process.html#child_process_child_process_spawnsync_command_args_options).
- This method throws an `Error` if the command fails.
- ### execa.shellSync(file, [options])
- Execute a command synchronously through the system shell.
- Returns the same result object as [`child_process.spawnSync`](https://nodejs.org/api/child_process.html#child_process_child_process_spawnsync_command_args_options).
- ### options
- Type: `Object`
- #### cwd
- Type: `string`<br>
- Default: `process.cwd()`
- Current working directory of the child process.
- #### env
- Type: `Object`<br>
- Default: `process.env`
- Environment key-value pairs. Extends automatically from `process.env`. Set `extendEnv` to `false` if you don't want this.
- #### extendEnv
- Type: `boolean`<br>
- Default: `true`
- Set to `false` if you don't want to extend the environment variables when providing the `env` property.
- #### argv0
- Type: `string`
- Explicitly set the value of `argv[0]` sent to the child process. This will be set to `command` or `file` if not specified.
- #### stdio
- Type: `string[]` `string`<br>
- Default: `pipe`
- Child's [stdio](https://nodejs.org/api/child_process.html#child_process_options_stdio) configuration.
- #### detached
- Type: `boolean`
- Prepare child to run independently of its parent process. Specific behavior [depends on the platform](https://nodejs.org/api/child_process.html#child_process_options_detached).
- #### uid
- Type: `number`
- Sets the user identity of the process.
- #### gid
- Type: `number`
- Sets the group identity of the process.
- #### shell
- Type: `boolean` `string`<br>
- Default: `false`
- If `true`, runs `command` 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.
- #### stripEof
- Type: `boolean`<br>
- Default: `true`
- [Strip EOF](https://github.com/sindresorhus/strip-eof) (last newline) from the output.
- #### preferLocal
- Type: `boolean`<br>
- Default: `true`
- Prefer locally installed binaries when looking for a binary to execute.<br>
- If you `$ npm install foo`, you can then `execa('foo')`.
- #### localDir
- Type: `string`<br>
- Default: `process.cwd()`
- Preferred path to find locally installed binaries in (use with `preferLocal`).
- #### input
- Type: `string` `Buffer` `stream.Readable`
- Write some input to the `stdin` of your binary.<br>
- Streams are not allowed when using the synchronous methods.
- #### reject
- Type: `boolean`<br>
- Default: `true`
- Setting this to `false` resolves the promise with the error instead of rejecting it.
- #### cleanup
- Type: `boolean`<br>
- Default: `true`
- Keep track of the spawned process and `kill` it when the parent process exits.
- #### encoding
- Type: `string`<br>
- Default: `utf8`
- Specify the character encoding used to decode the `stdout` and `stderr` output.
- #### timeout
- Type: `number`<br>
- Default: `0`
- If timeout is greater than `0`, the parent will send the signal identified by the `killSignal` property (the default is `SIGTERM`) if the child runs longer than timeout milliseconds.
- #### buffer
- Type: `boolean`<br>
- Default: `true`
- Buffer the output from the spawned process. When buffering is disabled you must consume the output of the `stdout` and `stderr` streams because the promise will not be resolved/rejected until they have completed.
- #### maxBuffer
- Type: `number`<br>
- Default: `10000000` (10MB)
- Largest amount of data in bytes allowed on `stdout` or `stderr`.
- #### killSignal
- Type: `string` `number`<br>
- Default: `SIGTERM`
- Signal value to be used when the spawned process will be killed.
- #### stdin
- Type: `string` `number` `Stream` `undefined` `null`<br>
- Default: `pipe`
- Same options as [`stdio`](https://nodejs.org/dist/latest-v6.x/docs/api/child_process.html#child_process_options_stdio).
- #### stdout
- Type: `string` `number` `Stream` `undefined` `null`<br>
- Default: `pipe`
- Same options as [`stdio`](https://nodejs.org/dist/latest-v6.x/docs/api/child_process.html#child_process_options_stdio).
- #### stderr
- Type: `string` `number` `Stream` `undefined` `null`<br>
- Default: `pipe`
- Same options as [`stdio`](https://nodejs.org/dist/latest-v6.x/docs/api/child_process.html#child_process_options_stdio).
- #### windowsVerbatimArguments
- Type: `boolean`<br>
- 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`.
- ## 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.
- ```js
- 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](https://sindresorhus.com)
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