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doc: refactor signal info in child_process.md
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* Since exec calls execFile and execFile internally calls spawn with
  options.signal, the signal parameter has been documented under exec
  as well.
* Refactor the description of signal under all the functions.
* Add examples of usage of signal under all the functions and add
  missing requires in the other examples.

PR-URL: #37528
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>
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RaisinTen authored and danielleadams committed Mar 16, 2021
1 parent 33436e3 commit f56a805
Showing 1 changed file with 50 additions and 6 deletions.
56 changes: 50 additions & 6 deletions doc/api/child_process.md
Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,9 @@ exec('"my script.cmd" a b', (err, stdout, stderr) => {
<!-- YAML
added: v0.1.90
changes:
- version: v15.4.0
pr-url: https://github.com/nodejs/node/pull/36308
description: AbortSignal support was added.
- version: v8.8.0
pr-url: https://github.com/nodejs/node/pull/15380
description: The `windowsHide` option is supported now.
Expand All @@ -160,6 +163,8 @@ changes:
* `shell` {string} Shell to execute the command with. See
[Shell requirements][] and [Default Windows shell][]. **Default:**
`'/bin/sh'` on Unix, `process.env.ComSpec` on Windows.
* `signal` {AbortSignal} allows aborting the child process using an
AbortSignal.
* `timeout` {number} **Default:** `0`
* `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
stderr. If exceeded, the child process is terminated and any output is
Expand All @@ -183,6 +188,8 @@ directly by the shell and special characters (vary based on
need to be dealt with accordingly:

```js
const { exec } = require('child_process');

exec('"/path/to/test file/test.sh" arg1 arg2');
// Double quotes are used so that the space in the path is not interpreted as
// a delimiter of multiple arguments.
Expand Down Expand Up @@ -246,6 +253,20 @@ async function lsExample() {
lsExample();
```

If the `signal` option is enabled, calling `.abort()` on the corresponding
`AbortController` is similar to calling `.kill()` on the child process except
the error passed to the callback will be an `AbortError`:

```js
const { exec } = require('child_process');
const controller = new AbortController();
const { signal } = controller;
const child = exec('grep ssh', { signal }, (error) => {
console.log(error); // an AbortError
});
controller.abort();
```

### `child_process.execFile(file[, args][, options][, callback])`
<!-- YAML
added: v0.1.91
Expand Down Expand Up @@ -280,7 +301,8 @@ changes:
`'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different
shell can be specified as a string. See [Shell requirements][] and
[Default Windows shell][]. **Default:** `false` (no shell).
* `signal` {AbortSignal} allows aborting the execFile using an AbortSignal.
* `signal` {AbortSignal} allows aborting the child process using an
AbortSignal.
* `callback` {Function} Called with the output when process terminates.
* `error` {Error}
* `stdout` {string|Buffer}
Expand Down Expand Up @@ -339,6 +361,7 @@ If the `signal` option is enabled, calling `.abort()` on the corresponding
the error passed to the callback will be an `AbortError`:

```js
const { execFile } = require('child_process');
const controller = new AbortController();
const { signal } = controller;
const child = execFile('node', ['--version'], { signal }, (error) => {
Expand Down Expand Up @@ -385,7 +408,8 @@ changes:
* `serialization` {string} Specify the kind of serialization used for sending
messages between processes. Possible values are `'json'` and `'advanced'`.
See [Advanced serialization][] for more details. **Default:** `'json'`.
* `signal` {AbortSignal} Allows closing the subprocess using an AbortSignal.
* `signal` {AbortSignal} Allows closing the child process using an
AbortSignal.
* `killSignal` {string} The signal value to be used when the spawned
process will be killed by the abort signal. **Default:** `'SIGTERM'`.
* `silent` {boolean} If `true`, stdin, stdout, and stderr of the child will be
Expand Down Expand Up @@ -429,8 +453,26 @@ current process.
The `shell` option available in [`child_process.spawn()`][] is not supported by
`child_process.fork()` and will be ignored if set.

The `signal` option works exactly the same way it does in
[`child_process.spawn()`][].
If the `signal` option is enabled, calling `.abort()` on the corresponding
`AbortController` is similar to calling `.kill()` on the child process except
the error passed to the callback will be an `AbortError`:

```js
if (process.argv[2] === 'child') {
setTimeout(() => {
console.log(`Hello from ${process.argv[2]}!`);
}, 1_000);
} else {
const { fork } = require('child_process');
const controller = new AbortController();
const { signal } = controller;
const child = fork(__filename, ['child'], { signal });
child.on('error', (err) => {
// This will be called with err being an AbortError if the controller aborts
});
controller.abort(); // Stops the child process
}
```

### `child_process.spawn(command[, args][, options])`
<!-- YAML
Expand Down Expand Up @@ -484,7 +526,8 @@ changes:
when `shell` is specified and is CMD. **Default:** `false`.
* `windowsHide` {boolean} Hide the subprocess console window that would
normally be created on Windows systems. **Default:** `false`.
* `signal` {AbortSignal} allows aborting the execFile using an AbortSignal.
* `signal` {AbortSignal} allows aborting the child process using an
AbortSignal.
* `killSignal` {string} The signal value to be used when the spawned
process will be killed by the abort signal. **Default:** `'SIGTERM'`.

Expand Down Expand Up @@ -599,13 +642,14 @@ If the `signal` option is enabled, calling `.abort()` on the corresponding
the error passed to the callback will be an `AbortError`:

```js
const { spawn } = require('child_process');
const controller = new AbortController();
const { signal } = controller;
const grep = spawn('grep', ['ssh'], { signal });
grep.on('error', (err) => {
// This will be called with err being an AbortError if the controller aborts
});
controller.abort(); // stops the process
controller.abort(); // Stops the child process
```

#### `options.detached`
Expand Down

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