A better
child_process
- Promise interface.
- Strips the final newline from the output so you don't have to do
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.
- Get interleaved output from
stdoutandstderrsimilar to what is printed on the terminal. (Async only) - Can specify command and arguments as a single string without a shell
- More descriptive errors.
$ npm install execa
const execa = require('execa');
(async () => {
const {stdout} = await execa('echo', ['unicorns']);
console.log(stdout);
//=> 'unicorns'
})();Additional examples:
const execa = require('execa');
(async () => {
// Pipe the child process stdout to the current stdout
execa('echo', ['unicorns']).stdout.pipe(process.stdout);
// Catching an error
try {
await execa('wrong command');
} catch (error) {
console.log(error);
/*
{
message: 'spawn wrong command ENOENT',
errno: 'ENOENT',
code: 'ENOENT',
syscall: 'spawn wrong command',
path: 'wrong command',
killed: false,
stdout: '',
stderr: '',
failed: true,
signal: null,
cmd: 'wrong command',
timedOut: false
}
*/
}
// Cancelling a spawned process
const subprocess = execa('node');
setTimeout(() => {
subprocess.cancel();
}, 1000);
try {
await subprocess;
} catch (error) {
console.log(subprocess.killed); // true
console.log(error.isCanceled); // true
}
})();
// Catching an error with a sync method
try {
execa.sync('wrong command');
} catch (error) {
console.log(error);
/*
{
message: 'spawnSync wrong command ENOENT',
errno: 'ENOENT',
code: 'ENOENT',
syscall: 'spawnSync wrong command',
path: 'wrong command',
}
*/
}Execute a file. Think of this as a mix of child_process.execFile() and child_process.spawn().
Arguments can be specified in either:
arguments:execa('echo', ['unicorns']).command:execa('echo unicorns').
Arguments should not be escaped nor quoted, except inside command where spaces can be escaped with a backslash.
Unless the shell option is used, no shell interpreter (Bash, cmd.exe, etc.) is used, so shell features such as variables substitution (echo $PATH) are not allowed.
Returns a child_process instance which:
- is also a
Promiseresolving or rejecting with achildProcessResult. - exposes the following additional methods and properties.
Similar to childProcess.kill(). This is preferred when cancelling the child process execution as the error is more descriptive and childProcessResult.isCanceled is set to true.
Stream combining/interleaving stdout and stderr.
Execute a file synchronously.
Returns or throws a childProcessResult.
Type: object
Result of a child process execution. On success this is a plain object. On failure this is also an Error instance.
Type: number
The numeric exit code of the process that was run.
Type: string
The textual exit code of the process that was run.
Type: string | Buffer
The output of the process on stdout.
Type: string | Buffer
The output of the process on stderr.
Type: string | Buffer
The output of the process on both stdout and stderr. undefined if execa.sync() was used.
Type: string
The command that was run.
Type: boolean
Whether the process failed to run.
Type: boolean
Whether the process timed out.
Type: boolean
Whether the process was killed.
Type: boolean
Whether the process was canceled.
Type: string | undefined
The signal that was used to terminate the process.
Type: object
Type: string
Default: process.cwd()
Current working directory of the child process.
Type: object
Default: process.env
Environment key-value pairs. Extends automatically from process.env. Set extendEnv to false if you don't want this.
Type: boolean
Default: true
8000
Set to false if you don't want to extend the environment variables when providing the env property.
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.
Type: string | string[]
Default: pipe
Child's stdio configuration.
Type: boolean
Prepare child to run independently of its parent process. Specific behavior depends on the platform.
Type: number
Sets the user identity of the process.
Type: number
Sets the group identity of the process.
Type: boolean | string
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.
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.
Type: boolean
Default: true
Strip the final newline character from the output.
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').
Type: string
Default: process.cwd()
Preferred path to find locally installed binaries in (use with preferLocal).
Type: string | Buffer | stream.Readable
Write some input to the stdin of your binary.
Streams are not allowed when using the synchronous methods.
Type: boolean
Default: true
Setting this to false resolves the promise with the error instead of rejecting it.
Type: boolean
Default: true
Kill the spawned process when the parent process exits unless either:
- the spawned process is detached
- the parent process is terminated abruptly, for example, with SIGKILL as opposed to SIGTERM or a normal exit
Type: string | null
Default: utf8
Specify the character encoding used to decode the stdout and stderr output. If set to null, then stdout and stderr will be a Buffer instead of a string.
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.
Type: boolean
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.
Type: number
Default: 10000000 (10MB)
Largest amount of data in bytes allowed on stdout or stderr.
Type: string | number
Default: SIGTERM
Signal value to be used when the spawned process will be killed.
Type: string | number | Stream | undefined
Default: pipe
Same options as stdio.
Type: string | number | Stream | undefined
Default: pipe
Same options as stdio.
Type: string | number | Stream | undefined
Default: pipe
Same options as stdio.
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.
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 subprocess = execa('echo', ['foo']);
subprocess.stdout.pipe(process.stdout);
(async () => {
const {stdout} = await subprocess;
console.log('child output:', stdout);
})();