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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 --save execa ``` ## Usage ```js 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. 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: `Array` `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. #### 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). ## 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)