[](https://codecov.io/gh/sindresorhus/execa)
> Process execution for humans
---
---
## Why
This package improves [`child_process`](https://nodejs.org/api/child_process.html) methods with:
- [Promise interface](#execacommandcommand-options).
- [Scripts interface](#scripts-interface), like `zx`.
- Improved [Windows support](https://github.com/IndigoUnited/node-cross-spawn#why), including [shebang](https://en.wikipedia.org/wiki/Shebang_(Unix)) binaries.
- Executes [locally installed binaries](#preferlocal) without `npx`.
- [Cleans up](#cleanup) child processes when the parent process ends.
- [Graceful termination](#optionsforcekillaftertimeout).
- Get [interleaved output](#all) from `stdout` and `stderr` similar to what is printed on the terminal.
- [Strips the final newline](#stripfinalnewline) from the output so you don't have to do `stdout.trim()`.
- Convenience methods to pipe processes' [input](#input) and [output](#redirect-output-to-a-file).
- Can specify file and arguments [as a single string](#execacommandcommand-options) without a shell.
- [Verbose mode](#verbose-mode) for debugging.
- More descriptive errors.
- Higher max buffer: 100 MB instead of 1 MB.
## Install
```sh
npm install execa
```
## Usage
### Promise interface
```js
import {execa} from 'execa';
const {stdout} = await execa('echo', ['unicorns']);
console.log(stdout);
//=> 'unicorns'
```
### Scripts interface
For more information about Execa scripts, please see [this page](docs/scripts.md).
#### Basic
```js
import {$} from 'execa';
const branch = await $`git branch --show-current`;
await $`dep deploy --branch=${branch}`;
```
#### Multiple arguments
```js
import {$} from 'execa';
const args = ['unicorns', '&', 'rainbows!'];
const {stdout} = await $`echo ${args}`;
console.log(stdout);
//=> 'unicorns & rainbows!'
```
#### With options
```js
import {$} from 'execa';
await $({stdio: 'inherit'})`echo unicorns`;
//=> 'unicorns'
```
#### Shared options
```js
import {$} from 'execa';
const $$ = $({stdio: 'inherit'});
await $$`echo unicorns`;
//=> 'unicorns'
await $$`echo rainbows`;
//=> 'rainbows'
```
#### Verbose mode
```sh
> 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
```
### Input/output
#### Redirect output to a file
```js
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');
```
#### Redirect input from a file
```js
import {execa} from 'execa';
// Similar to `cat < stdin.txt` in Bash
const {stdout} = await execa('cat', {inputFile: 'stdin.txt'});
console.log(stdout);
//=> 'unicorns'
```
#### Save and pipe output from a child process
```js
import {execa} from 'execa';
const {stdout} = await execa('echo', ['unicorns']).pipeStdout(process.stdout);
// Prints `unicorns`
console.log(stdout);
// Also returns 'unicorns'
```
#### Pipe multiple processes
```js
import {execa} from 'execa';
// Similar to `echo unicorns | cat` in Bash
const {stdout} = await execa('echo', ['unicorns']).pipeStdout(execa('cat'));
console.log(stdout);
//=> 'unicorns'
```
### Handling Errors
```js
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,
killed: false
}
*/
}
```
### Graceful termination
Using SIGTERM, and after 2 seconds, kill it with SIGKILL.
```js
const subprocess = execa('node');
setTimeout(() => {
subprocess.kill('SIGTERM', {
forceKillAfterTimeout: 2000
});
}, 1000);
```
## API
### Methods
#### execa(file, arguments?, options?)
Executes a command using `file ...arguments`. `arguments` are specified as an array of strings. Returns a [`childProcess`](#childprocess).
Arguments are [automatically escaped](#shell-syntax). They can contain any character, including spaces.
This is the preferred method when executing single commands.
#### execaNode(scriptPath, arguments?, options?)
Executes a Node.js file using `node scriptPath ...arguments`. `arguments` are specified as an array of strings. Returns a [`childProcess`](#childprocess).
Arguments are [automatically escaped](#shell-syntax). They can contain any character, including spaces.
This is the preferred method when executing Node.js files.
Like [`child_process#fork()`](https://nodejs.org/api/child_process.html#child_process_child_process_fork_modulepath_args_options):
- the current Node version and options are used. This can be overridden using the [`nodePath`](#nodepath-for-node-only) and [`nodeOptions`](#nodeoptions-for-node-only) options.
- the [`shell`](#shell) option cannot be used
- an extra channel [`ipc`](https://nodejs.org/api/child_process.html#child_process_options_stdio) is passed to [`stdio`](#stdio)
#### $\`command\`
Executes a command. The `command` string includes both the `file` and its `arguments`. Returns a [`childProcess`](#childprocess).
Arguments are [automatically escaped](#shell-syntax). 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`](#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](#scripts-interface) and [this page](docs/scripts.md).
#### $(options)
Returns a new instance of [`$`](#command) 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`; ``
#### execaCommand(command, options?)
Executes a command. The `command` string includes both the `file` and its `arguments`. Returns a [`childProcess`](#childprocess).
Arguments are [automatically escaped](#shell-syntax). 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.
### execaSync(file, arguments?, options?)
Same as [`execa()`](#execacommandcommand-options) but synchronous.
Returns or throws a [`childProcessResult`](#childProcessResult).
### $.sync\`command\`
Same as [$\`command\`](#command) but synchronous.
Returns or throws a [`childProcessResult`](#childProcessResult).
### execaCommandSync(command, options?)
Same as [`execaCommand()`](#execacommand-command-options) but synchronous.
Returns or throws a [`childProcessResult`](#childProcessResult).
### Shell syntax
For all the [methods above](#methods), no shell interpreter (Bash, cmd.exe, etc.) is used unless the [`shell` option](#shell) is set. This means shell-specific characters and expressions (`$variable`, `&&`, `||`, `;`, `|`, etc.) have no special meaning and do not need to be escaped.
### childProcess
The return value of all [asynchronous methods](#methods) is both:
- a `Promise` resolving or rejecting with a [`childProcessResult`](#childProcessResult).
- a [`child_process` instance](https://nodejs.org/api/child_process.html#child_process_class_childprocess) with the following additional methods and properties.
#### kill(signal?, options?)
Same as the original [`child_process#kill()`](https://nodejs.org/api/child_process.html#child_process_subprocess_kill_signal) except: if `signal` is `SIGTERM` (the default value) and the child process is not terminated after 5 seconds, force it by sending `SIGKILL`.
Note that this graceful termination does not work on Windows, because Windows [doesn't support signals](https://nodejs.org/api/process.html#process_signal_events) (`SIGKILL` and `SIGTERM` has the same effect of force-killing the process immediately.) If you want to achieve graceful termination on Windows, you have to use other means, such as [`taskkill`](https://github.com/sindresorhus/taskkill).
##### options.forceKillAfterTimeout
Type: `number | false`\
Default: `5000`
Milliseconds to wait for the child process to terminate before sending `SIGKILL`.
Can be disabled with `false`.
#### all
Type: `ReadableStream | undefined`
Stream combining/interleaving [`stdout`](https://nodejs.org/api/child_process.html#child_process_subprocess_stdout) and [`stderr`](https://nodejs.org/api/child_process.html#child_process_subprocess_stderr).
This is `undefined` if either:
- the [`all` option](#all-2) is `false` (the default value)
- both [`stdout`](#stdout-1) and [`stderr`](#stderr-1) options are set to [`'inherit'`, `'ipc'`, `Stream` or `integer`](https://nodejs.org/dist/latest-v6.x/docs/api/child_process.html#child_process_options_stdio)
#### pipeStdout(target)
[Pipe](https://nodejs.org/api/stream.html#readablepipedestination-options) the child process's `stdout` to `target`, which can be:
- Another [`execa()` return value](#pipe-multiple-processes)
- A [writable stream](#save-and-pipe-output-from-a-child-process)
- A [file path string](#redirect-output-to-a-file)
If the `target` is another [`execa()` return value](#execacommandcommand-options), it is returned. Otherwise, the original `execa()` return value is returned. This allows chaining `pipeStdout()` then `await`ing the [final result](#childprocessresult).
The [`stdout` option](#stdout-1) must be kept as `pipe`, its default value.
#### pipeStderr(target)
Like [`pipeStdout()`](#pipestdouttarget) but piping the child process's `stderr` instead.
The [`stderr` option](#stderr-1) must be kept as `pipe`, its default value.
#### pipeAll(target)
Combines both [`pipeStdout()`](#pipestdouttarget) and [`pipeStderr()`](#pipestderrtarget).
Either the [`stdout` option](#stdout-1) or the [`stderr` option](#stderr-1) must be kept as `pipe`, their default value. Also, the [`all` option](#all-2) must be set to `true`.
### childProcessResult
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](#failed) when:
- its [exit code](#exitcode) is not `0`
- it was [killed](#killed) with a [signal](#signal)
- [timing out](#timedout)
- [being canceled](#iscanceled)
- there's not enough memory or there are already too many child processes
#### command
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()`](#execafile-arguments-options) or [`execaCommand()`](#execacommandcommand-options).
#### escapedCommand
Type: `string`
Same as [`command`](#command-1) 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()`](#execafile-arguments-options) or [`execaCommand()`](#execacommandcommand-options).
#### exitCode
Type: `number`
The numeric exit code of the process that was run.
#### stdout
Type: `string | Buffer`
The output of the process on stdout.
#### stderr
Type: `string | Buffer`
The output of the process on stderr.
#### all
Type: `string | Buffer | undefined`
The output of the process with `stdout` and `stderr` interleaved.
This is `undefined` if either:
- the [`all` option](#all-2) is `false` (the default value)
- `execaSync()` was used
#### failed
Type: `boolean`
Whether the process failed to run.
#### timedOut
Type: `boolean`
Whether the process timed out.
#### isCanceled
Type: `boolean`
Whether the process was canceled.
You can cancel the spawned process using the [`signal`](#signal-1) option.
#### killed
Type: `boolean`
Whether the process was killed.
#### signal
Type: `string | undefined`
The name of the signal that was used to terminate the process. For example, `SIGFPE`.
If a signal terminated the process, this property is defined and included in the error message. Otherwise it is `undefined`.
#### signalDescription
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.
#### cwd
Type: `string`
The `cwd` of the command if provided in the [command options](#cwd-1). Otherwise it is `process.cwd()`.
#### message
Type: `string`
Error message when the child process failed to run. In addition to the [underlying error message](#originalMessage), it also contains some information related to why the child process errored.
The child process [stderr](#stderr) then [stdout](#stdout) are appended to the end, separated with newlines and not interleaved.
#### shortMessage
Type: `string`
This is the same as the [`message` property](#message) except it does not include the child process stdout/stderr.
#### originalMessage
Type: `string | undefined`
Original error message. This is the same as the `message` property except it includes neither the child process stdout/stderr nor some additional information added by Execa.
This is `undefined` unless the child process exited due to an `error` event or a timeout.
### options
Type: `object`
#### cleanup
Type: `boolean`\
Default: `true`
Kill the spawned process when the parent process exits unless either:
- the spawned process is [`detached`](https://nodejs.org/api/child_process.html#child_process_options_detached)
- the parent process is terminated abruptly, for example, with `SIGKILL` as opposed to `SIGTERM` or a normal exit
#### preferLocal
Type: `boolean`\
Default: `true` with [`$`](#command), `false` otherwise
Prefer locally installed binaries when looking for a binary to execute.\
If you `$ npm install foo`, you can then `execa('foo')`.
#### localDir
Type: `string | URL`\
Default: `process.cwd()`
Preferred path to find locally installed binaries in (use with `preferLocal`).
#### execPath
Type: `string`\
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](#cwd).
Requires [`preferLocal`](#preferlocal) to be `true`.
For example, this can be used together with [`get-node`](https://github.com/ehmicky/get-node) to run a specific Node.js version in a child process.
#### buffer
Type: `boolean`\
Default: `true`
Buffer the output from the spawned process. When set to `false`, you must read the output of [`stdout`](#stdout-1) and [`stderr`](#stderr-1) (or [`all`](#all) if the [`all`](#all-2) option is `true`). Otherwise the returned promise will not be resolved/rejected.
If the spawned process fails, [`error.stdout`](#stdout), [`error.stderr`](#stderr), and [`error.all`](#all) will contain the buffered data.
#### input
Type: `string | Buffer | stream.Readable`
Write some input to the `stdin` of your binary.\
Streams are not allowed when using the synchronous methods.
If the input is a file, use the [`inputFile` option](#inputfile) instead.
#### inputFile
Type: `string`
Use a file as input to the the `stdin` of your binary.
If the input is not a file, use the [`input` option](#input) instead.
#### stdin
Type: `string | number | Stream | undefined`\
Default: `inherit` with [`$`](#command), `pipe` otherwise
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`\
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`\
Default: `pipe`
Same options as [`stdio`](https://nodejs.org/dist/latest-v6.x/docs/api/child_process.html#child_process_options_stdio).
#### all
Type: `boolean`\
Default: `false`
Add an `.all` property on the [promise](#all) and the [resolved value](#all-1). The property contains the output of the process with `stdout` and `stderr` interleaved.
#### reject
Type: `boolean`\
Default: `true`
Setting this to `false` resolves the promise with the error instead of rejecting it.
#### stripFinalNewline
Type: `boolean`\
Default: `true`
Strip the final [newline character](https://en.wikipedia.org/wiki/Newline) from the output.
#### extendEnv
Type: `boolean`\
Default: `true`
Set to `false` if you don't want to extend the environment variables when providing the `env` property.
---
Execa also accepts the below options which are the same as the options for [`child_process#spawn()`](https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options)/[`child_process#exec()`](https://nodejs.org/api/child_process.html#child_process_child_process_exec_command_options_callback)
#### cwd
Type: `string | URL`\
Default: `process.cwd()`
Current working directory of the child process.
#### env
Type: `object`\
Default: `process.env`
Environment key-value pairs. Extends automatically from `process.env`. Set [`extendEnv`](#extendenv) to `false` if you don't want this.
#### argv0
Type: `string`
Explicitly set the value of `argv[0]` sent to the child process. This will be set to `file` if not specified.
#### stdio
Type: `string | string[]`\
Default: `pipe`
Child's [stdio](https://nodejs.org/api/child_process.html#child_process_options_stdio) configuration.
#### serialization
Type: `string`\
Default: `'json'`
Specify the kind of serialization used for sending messages between processes when using the [`stdio: 'ipc'`](#stdio) option or [`execaNode()`](#execanodescriptpath-arguments-options):
- `json`: Uses `JSON.stringify()` and `JSON.parse()`.
- `advanced`: Uses [`v8.serialize()`](https://nodejs.org/api/v8.html#v8_v8_serialize_value)
[More info.](https://nodejs.org/api/child_process.html#child_process_advanced_serialization)
#### 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`\
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.
#### encoding
Type: `string | null`\
Default: `utf8`
Specify the character encoding used to decode the `stdout` and `stderr` output. If set to `'buffer'` or `null`, then `stdout` and `stderr` will be a `Buffer` instead of a string.
#### timeout
Type: `number`\
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`\
Default: `100_000_000` (100 MB)
Largest amount of data in bytes allowed on `stdout` or `stderr`.
#### killSignal
Type: `string | number`\
Default: `SIGTERM`
Signal value to be used when the spawned process will be killed.
#### signal
Type: [`AbortSignal`](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal)
You can abort the spawned process using [`AbortController`](https://developer.mozilla.org/en-US/docs/Web/API/AbortController).
When `AbortController.abort()` is called, [`.isCanceled`](#iscanceled) becomes `true`.
#### windowsVerbatimArguments
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`.
#### windowsHide
Type: `boolean`\
Default: `true`
On Windows, do not create a new console window. Please note this also prevents `CTRL-C` [from working](https://github.com/nodejs/node/issues/29837) on Windows.
#### verbose
Type: `boolean`\
Default: `false`
[Print each command](#verbose-mode) on `stderr` before executing it.
This can also be enabled by setting the `NODE_DEBUG=execa` environment variable in the current process.
#### nodePath *(For `.node()` only)*
Type: `string`\
Default: [`process.execPath`](https://nodejs.org/api/process.html#process_process_execpath)
Node.js executable used to create the child process.
#### nodeOptions *(For `.node()` only)*
Type: `string[]`\
Default: [`process.execArgv`](https://nodejs.org/api/process.html#process_process_execargv)
List of [CLI options](https://nodejs.org/api/cli.html#cli_options) passed to the Node.js executable.
## Tips
### Retry on error
Gracefully handle failures by using automatic retries and exponential backoff with the [`p-retry`](https://github.com/sindresorhus/p-retry) package:
```js
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}));
```
### Cancelling a spawned process
```js
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(subprocess.killed); // true
console.log(error.isCanceled); // true
}
```
### Execute the current package's binary
```js
import {getBinPath} from 'get-bin-path';
const binPath = await getBinPath();
await execa(binPath);
```
`execa` can be combined with [`get-bin-path`](https://github.com/ehmicky/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.
## Related
- [gulp-execa](https://github.com/ehmicky/gulp-execa) - Gulp plugin for `execa`
- [nvexeca](https://github.com/ehmicky/nvexeca) - Run `execa` using any Node.js version
- [sudo-prompt](https://github.com/jorangreef/sudo-prompt) - Run commands with elevated privileges.
## Maintainers
- [Sindre Sorhus](https://github.com/sindresorhus)
- [@ehmicky](https://github.com/ehmicky)
---
