67 lines
2.8 KiB
Markdown
67 lines
2.8 KiB
Markdown
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# spawn-async [](https://circleci.com/gh/expo/spawn-async) [](https://travis-ci.org/expo/spawn-async)
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A cross-platform version of Node's `child_process.spawn` as an async function that returns a promise. Supports Node 8 LTS and up.
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## Usage:
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```js
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import spawnAsync from '@expo/spawn-async';
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(async function () {
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let resultPromise = spawnAsync('echo', ['hello', 'world']);
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let spawnedChildProcess = resultPromise.child;
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try {
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let {
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pid,
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output: [stdout, stderr],
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stdout,
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stderr,
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status,
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signal,
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} = await resultPromise;
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} catch (e) {
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console.error(e.stack);
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// The error object also has the same properties as the result object
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}
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})();
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```
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## API
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`spawnAsync` takes the same arguments as [`child_process.spawn`](https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options). Its options are the same as those of `child_process.spawn` plus:
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- `ignoreStdio`: whether to ignore waiting for the child process's stdio streams to close before resolving the result promise. When ignoring stdio, the returned values for `stdout` and `stderr` will be empty strings. The default value of this option is `false`.
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It returns a promise whose result is an object with these properties:
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- `pid`: the process ID of the spawned child process
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- `output`: an array with stdout and stderr's output
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- `stdout`: a string of what the child process wrote to stdout
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- `stderr`: a string of what the child process wrote to stderr
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- `status`: the exit code of the child process
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- `signal`: the signal (ex: `SIGTERM`) used to stop the child process if it did not exit on its own
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If there's an error running the child process or it exits with a non-zero status code, `spawnAsync` rejects the returned promise. The Error object also has the properties listed above.
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### Accessing the child process
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Sometimes you may want to access the child process object--for example, if you wanted to attach event handlers to `stdio` or `stderr` and process data as it is available instead of waiting for the process to be resolved.
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You can do this by accessing `.child` on the Promise that is returned by `spawnAsync`.
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Here is an example:
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```js
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(async () => {
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let ffmpeg$ = spawnAsync('ffmpeg', ['-i', 'path/to/source.flac', '-codec:a', 'libmp3lame', '-b:a', '320k', '-ar', '44100', 'path/to/output.mp3']);
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let childProcess = ffmpeg$.child;
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childProcess.stdout.on('data', (data) => {
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console.log(`ffmpeg stdout: ${data}`);
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});
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childProcess.stderr.on('data', (data) => {
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console.error(`ffmpeg stderr: ${data}`);
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});
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let result = await ffmpeg$;
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console.log(`ffmpeg pid ${result.pid} exited with code ${result.code}`);
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})();
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```
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