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