readme.md 8.1KB
execa 
A better
child_process
Why
- Promise interface.
- Strips EOF from the output so you don’t have to
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.
Install
$ npm install execa
<img src="https://c5.patreon.com/external/logo/become_a_patron_button@2x.png" width="160">
Usage
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);
// 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, 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.
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.
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.
options
Type: Object
cwd
Type: string
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 to false if you don’t want this.
extendEnv
Type: boolean
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
Default: pipe
Child’s stdio configuration.
detached
Type: boolean
Prepare child to run independently of its parent process. Specific behavior depends on the platform.
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 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
Default: true
Strip EOF (last newline) from the output.
preferLocal
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').
localDir
Type: string
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.
Streams are not allowed when using the synchronous methods.
reject
Type: boolean
Default: true
Setting this to false resolves the promise with the error instead of rejecting it.
cleanup
Type: boolean
Default: true
Keep track of the spawned process and kill it when the parent process exits.
encoding
Type: string
Default: utf8
Specify the character encoding used to decode the stdout and stderr output.
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.
buffer
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.
maxBuffer
Type: number
Default: 10000000 (10MB)
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.
stdin
Type: string number Stream undefined null
Default: pipe
Same options as stdio.
stdout
Type: string number Stream undefined null
Default: pipe
Same options as stdio.
stderr
Type: string number Stream undefined null
Default: pipe
Same options as stdio.
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.
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.
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