1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
|
# Child process
<!--introduced_in=v0.10.0-->
> Stability: 2 - Stable
<!-- source_link=lib/child_process.js -->
The `child_process` module provides the ability to spawn subprocesses in
a manner that is similar, but not identical, to popen(3). This capability
is primarily provided by the [`child_process.spawn()`][] function:
```js
const { spawn } = require('child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.error(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
```
By default, pipes for `stdin`, `stdout`, and `stderr` are established between
the parent Node.js process and the spawned subprocess. These pipes have
limited (and platform-specific) capacity. If the subprocess writes to
stdout in excess of that limit without the output being captured, the
subprocess blocks waiting for the pipe buffer to accept more data. This is
identical to the behavior of pipes in the shell. Use the `{ stdio: 'ignore' }`
option if the output will not be consumed.
The command lookup is performed using the `options.env.PATH` environment
variable if it is in the `options` object. Otherwise, `process.env.PATH` is
used.
On Windows, environment variables are case-insensitive. Node.js
lexicographically sorts the `env` keys and uses the first one that
case-insensitively matches. Only first (in lexicographic order) entry will be
passed to the subprocess. This might lead to issues on Windows when passing
objects to the `env` option that have multiple variants of the same key, such as
`PATH` and `Path`.
The [`child_process.spawn()`][] method spawns the child process asynchronously,
without blocking the Node.js event loop. The [`child_process.spawnSync()`][]
function provides equivalent functionality in a synchronous manner that blocks
the event loop until the spawned process either exits or is terminated.
For convenience, the `child_process` module provides a handful of synchronous
and asynchronous alternatives to [`child_process.spawn()`][] and
[`child_process.spawnSync()`][]. Each of these alternatives are implemented on
top of [`child_process.spawn()`][] or [`child_process.spawnSync()`][].
* [`child_process.exec()`][]: spawns a shell and runs a command within that
shell, passing the `stdout` and `stderr` to a callback function when
complete.
* [`child_process.execFile()`][]: similar to [`child_process.exec()`][] except
that it spawns the command directly without first spawning a shell by
default.
* [`child_process.fork()`][]: spawns a new Node.js process and invokes a
specified module with an IPC communication channel established that allows
sending messages between parent and child.
* [`child_process.execSync()`][]: a synchronous version of
[`child_process.exec()`][] that will block the Node.js event loop.
* [`child_process.execFileSync()`][]: a synchronous version of
[`child_process.execFile()`][] that will block the Node.js event loop.
For certain use cases, such as automating shell scripts, the
[synchronous counterparts][] may be more convenient. In many cases, however,
the synchronous methods can have significant impact on performance due to
stalling the event loop while spawned processes complete.
## Asynchronous process creation
The [`child_process.spawn()`][], [`child_process.fork()`][], [`child_process.exec()`][],
and [`child_process.execFile()`][] methods all follow the idiomatic asynchronous
programming pattern typical of other Node.js APIs.
Each of the methods returns a [`ChildProcess`][] instance. These objects
implement the Node.js [`EventEmitter`][] API, allowing the parent process to
register listener functions that are called when certain events occur during
the life cycle of the child process.
The [`child_process.exec()`][] and [`child_process.execFile()`][] methods
additionally allow for an optional `callback` function to be specified that is
invoked when the child process terminates.
### Spawning `.bat` and `.cmd` files on Windows
The importance of the distinction between [`child_process.exec()`][] and
[`child_process.execFile()`][] can vary based on platform. On Unix-type
operating systems (Unix, Linux, macOS) [`child_process.execFile()`][] can be
more efficient because it does not spawn a shell by default. On Windows,
however, `.bat` and `.cmd` files are not executable on their own without a
terminal, and therefore cannot be launched using [`child_process.execFile()`][].
When running on Windows, `.bat` and `.cmd` files can be invoked using
[`child_process.spawn()`][] with the `shell` option set, with
[`child_process.exec()`][], or by spawning `cmd.exe` and passing the `.bat` or
`.cmd` file as an argument (which is what the `shell` option and
[`child_process.exec()`][] do). In any case, if the script filename contains
spaces it needs to be quoted.
```js
// On Windows Only...
const { spawn } = require('child_process');
const bat = spawn('cmd.exe', ['/c', 'my.bat']);
bat.stdout.on('data', (data) => {
console.log(data.toString());
});
bat.stderr.on('data', (data) => {
console.error(data.toString());
});
bat.on('exit', (code) => {
console.log(`Child exited with code ${code}`);
});
```
```js
// OR...
const { exec, spawn } = require('child_process');
exec('my.bat', (err, stdout, stderr) => {
if (err) {
console.error(err);
return;
}
console.log(stdout);
});
// Script with spaces in the filename:
const bat = spawn('"my script.cmd"', ['a', 'b'], { shell: true });
// or:
exec('"my script.cmd" a b', (err, stdout, stderr) => {
// ...
});
```
### `child_process.exec(command[, options][, callback])`
<!-- YAML
added: v0.1.90
changes:
- version:
- v16.4.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/38862
description: The `cwd` option can be a WHATWG `URL` object using
`file:` protocol.
- 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.
-->
* `command` {string} The command to run, with space-separated arguments.
* `options` {Object}
* `cwd` {string|URL} Current working directory of the child process.
**Default:** `process.cwd()`.
* `env` {Object} Environment key-value pairs. **Default:** `process.env`.
* `encoding` {string} **Default:** `'utf8'`
* `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
truncated. See caveat at [`maxBuffer` and Unicode][].
**Default:** `1024 * 1024`.
* `killSignal` {string|integer} **Default:** `'SIGTERM'`
* `uid` {number} Sets the user identity of the process (see setuid(2)).
* `gid` {number} Sets the group identity of the process (see setgid(2)).
* `windowsHide` {boolean} Hide the subprocess console window that would
normally be created on Windows systems. **Default:** `false`.
* `callback` {Function} called with the output when process terminates.
* `error` {Error}
* `stdout` {string|Buffer}
* `stderr` {string|Buffer}
* Returns: {ChildProcess}
Spawns a shell then executes the `command` within that shell, buffering any
generated output. The `command` string passed to the exec function is processed
directly by the shell and special characters (vary based on
[shell](https://en.wikipedia.org/wiki/List_of_command-line_interpreters))
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.
exec('echo "The \\$HOME variable is $HOME"');
// The $HOME variable is escaped in the first instance, but not in the second.
```
**Never pass unsanitized user input to this function. Any input containing shell
metacharacters may be used to trigger arbitrary command execution.**
If a `callback` function is provided, it is called with the arguments
`(error, stdout, stderr)`. On success, `error` will be `null`. On error,
`error` will be an instance of [`Error`][]. The `error.code` property will be
the exit code of the process. By convention, any exit code other than `0`
indicates an error. `error.signal` will be the signal that terminated the
process.
The `stdout` and `stderr` arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The `encoding` option
can be used to specify the character encoding used to decode the stdout and
stderr output. If `encoding` is `'buffer'`, or an unrecognized character
encoding, `Buffer` objects will be passed to the callback instead.
```js
const { exec } = require('child_process');
exec('cat *.js missing_file | wc -l', (error, stdout, stderr) => {
if (error) {
console.error(`exec error: ${error}`);
return;
}
console.log(`stdout: ${stdout}`);
console.error(`stderr: ${stderr}`);
});
```
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.
Unlike the exec(3) POSIX system call, `child_process.exec()` does not replace
the existing process and uses a shell to execute the command.
If this method is invoked as its [`util.promisify()`][]ed version, it returns
a `Promise` for an `Object` with `stdout` and `stderr` properties. The returned
`ChildProcess` instance is attached to the `Promise` as a `child` property. In
case of an error (including any error resulting in an exit code other than 0), a
rejected promise is returned, with the same `error` object given in the
callback, but with two additional properties `stdout` and `stderr`.
```js
const util = require('util');
const exec = util.promisify(require('child_process').exec);
async function lsExample() {
const { stdout, stderr } = await exec('ls');
console.log('stdout:', stdout);
console.error('stderr:', stderr);
}
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
changes:
- version:
- v16.4.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/38862
description: The `cwd` option can be a WHATWG `URL` object using
`file:` protocol.
- version:
- v15.4.0
- v14.17.0
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.
-->
* `file` {string} The name or path of the executable file to run.
* `args` {string[]} List of string arguments.
* `options` {Object}
* `cwd` {string|URL} Current working directory of the child process.
* `env` {Object} Environment key-value pairs. **Default:** `process.env`.
* `encoding` {string} **Default:** `'utf8'`
* `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
truncated. See caveat at [`maxBuffer` and Unicode][].
**Default:** `1024 * 1024`.
* `killSignal` {string|integer} **Default:** `'SIGTERM'`
* `uid` {number} Sets the user identity of the process (see setuid(2)).
* `gid` {number} Sets the group identity of the process (see setgid(2)).
* `windowsHide` {boolean} Hide the subprocess console window that would
normally be created on Windows systems. **Default:** `false`.
* `windowsVerbatimArguments` {boolean} No quoting or escaping of arguments is
done on Windows. Ignored on Unix. **Default:** `false`.
* `shell` {boolean|string} If `true`, runs `command` inside of a shell. Uses
`'/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 child process using an
AbortSignal.
* `callback` {Function} Called with the output when process terminates.
* `error` {Error}
* `stdout` {string|Buffer}
* `stderr` {string|Buffer}
* Returns: {ChildProcess}
The `child_process.execFile()` function is similar to [`child_process.exec()`][]
except that it does not spawn a shell by default. Rather, the specified
executable `file` is spawned directly as a new process making it slightly more
efficient than [`child_process.exec()`][].
The same options as [`child_process.exec()`][] are supported. Since a shell is
not spawned, behaviors such as I/O redirection and file globbing are not
supported.
```js
const { execFile } = require('child_process');
const child = execFile('node', ['--version'], (error, stdout, stderr) => {
if (error) {
throw error;
}
console.log(stdout);
});
```
The `stdout` and `stderr` arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The `encoding` option
can be used to specify the character encoding used to decode the stdout and
stderr output. If `encoding` is `'buffer'`, or an unrecognized character
encoding, `Buffer` objects will be passed to the callback instead.
If this method is invoked as its [`util.promisify()`][]ed version, it returns
a `Promise` for an `Object` with `stdout` and `stderr` properties. The returned
`ChildProcess` instance is attached to the `Promise` as a `child` property. In
case of an error (including any error resulting in an exit code other than 0), a
rejected promise is returned, with the same `error` object given in the
callback, but with two additional properties `stdout` and `stderr`.
```js
const util = require('util');
const execFile = util.promisify(require('child_process').execFile);
async function getVersion() {
const { stdout } = await execFile('node', ['--version']);
console.log(stdout);
}
getVersion();
```
**If the `shell` option is enabled, do not pass unsanitized user input to this
function. Any input containing shell metacharacters may be used to trigger
arbitrary command execution.**
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 { execFile } = require('child_process');
const controller = new AbortController();
const { signal } = controller;
const child = execFile('node', ['--version'], { signal }, (error) => {
console.log(error); // an AbortError
});
controller.abort();
```
### `child_process.fork(modulePath[, args][, options])`
<!-- YAML
added: v0.5.0
changes:
- version:
- v16.4.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/38862
description: The `cwd` option can be a WHATWG `URL` object using
`file:` protocol.
- version:
- v15.13.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/37256
description: timeout was added.
- version:
- v15.11.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/37325
description: killSignal for AbortSignal was added.
- version:
- v15.6.0
- v14.17.0
pr-url: https://github.com/nodejs/node/pull/36603
description: AbortSignal support was added.
- version:
- v13.2.0
- v12.16.0
pr-url: https://github.com/nodejs/node/pull/30162
description: The `serialization` option is supported now.
- version: v8.0.0
pr-url: https://github.com/nodejs/node/pull/10866
description: The `stdio` option can now be a string.
- version: v6.4.0
pr-url: https://github.com/nodejs/node/pull/7811
description: The `stdio` option is supported now.
-->
* `modulePath` {string} The module to run in the child.
* `args` {string[]} List of string arguments.
* `options` {Object}
* `cwd` {string|URL} Current working directory of the child process.
* `detached` {boolean} Prepare child to run independently of its parent
process. Specific behavior depends on the platform, see
[`options.detached`][]).
* `env` {Object} Environment key-value pairs. **Default:** `process.env`.
* `execPath` {string} Executable used to create the child process.
* `execArgv` {string[]} List of string arguments passed to the executable.
**Default:** `process.execArgv`.
* `gid` {number} Sets the group identity of the process (see setgid(2)).
* `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 child process using an
AbortSignal.
* `killSignal` {string|integer} The signal value to be used when the spawned
process will be killed by timeout or abort signal. **Default:** `'SIGTERM'`.
* `silent` {boolean} If `true`, stdin, stdout, and stderr of the child will be
piped to the parent, otherwise they will be inherited from the parent, see
the `'pipe'` and `'inherit'` options for [`child_process.spawn()`][]'s
[`stdio`][] for more details. **Default:** `false`.
* `stdio` {Array|string} See [`child_process.spawn()`][]'s [`stdio`][].
When this option is provided, it overrides `silent`. If the array variant
is used, it must contain exactly one item with value `'ipc'` or an error
will be thrown. For instance `[0, 1, 2, 'ipc']`.
* `uid` {number} Sets the user identity of the process (see setuid(2)).
* `windowsVerbatimArguments` {boolean} No quoting or escaping of arguments is
done on Windows. Ignored on Unix. **Default:** `false`.
* `timeout` {number} In milliseconds the maximum amount of time the process
is allowed to run. **Default:** `undefined`.
* Returns: {ChildProcess}
The `child_process.fork()` method is a special case of
[`child_process.spawn()`][] used specifically to spawn new Node.js processes.
Like [`child_process.spawn()`][], a [`ChildProcess`][] object is returned. The
returned [`ChildProcess`][] will have an additional communication channel
built-in that allows messages to be passed back and forth between the parent and
child. See [`subprocess.send()`][] for details.
Keep in mind that spawned Node.js child processes are
independent of the parent with exception of the IPC communication channel
that is established between the two. Each process has its own memory, with
their own V8 instances. Because of the additional resource allocations
required, spawning a large number of child Node.js processes is not
recommended.
By default, `child_process.fork()` will spawn new Node.js instances using the
[`process.execPath`][] of the parent process. The `execPath` property in the
`options` object allows for an alternative execution path to be used.
Node.js processes launched with a custom `execPath` will communicate with the
parent process using the file descriptor (fd) identified using the
environment variable `NODE_CHANNEL_FD` on the child process.
Unlike the fork(2) POSIX system call, `child_process.fork()` does not clone the
current process.
The `shell` option available in [`child_process.spawn()`][] is not supported by
`child_process.fork()` and will be ignored if set.
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
added: v0.1.90
changes:
- version:
- v16.4.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/38862
description: The `cwd` option can be a WHATWG `URL` object using
`file:` protocol.
- version:
- v15.13.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/37256
description: timeout was added.
- version:
- v15.11.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/37325
description: killSignal for AbortSignal was added.
- version:
- v15.5.0
- v14.17.0
pr-url: https://github.com/nodejs/node/pull/36432
description: AbortSignal support was added.
- version:
- v13.2.0
- v12.16.0
pr-url: https://github.com/nodejs/node/pull/30162
description: The `serialization` option is supported now.
- version: v8.8.0
pr-url: https://github.com/nodejs/node/pull/15380
description: The `windowsHide` option is supported now.
- version: v6.4.0
pr-url: https://github.com/nodejs/node/pull/7696
description: The `argv0` option is supported now.
- version: v5.7.0
pr-url: https://github.com/nodejs/node/pull/4598
description: The `shell` option is supported now.
-->
* `command` {string} The command to run.
* `args` {string[]} List of string arguments.
* `options` {Object}
* `cwd` {string|URL} Current working directory of the child process.
* `env` {Object} Environment key-value pairs. **Default:** `process.env`.
* `argv0` {string} Explicitly set the value of `argv[0]` sent to the child
process. This will be set to `command` if not specified.
* `stdio` {Array|string} Child's stdio configuration (see
[`options.stdio`][`stdio`]).
* `detached` {boolean} Prepare child to run independently of its parent
process. Specific behavior depends on the platform, see
[`options.detached`][]).
* `uid` {number} Sets the user identity of the process (see setuid(2)).
* `gid` {number} Sets the group identity of the process (see setgid(2)).
* `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'`.
* `shell` {boolean|string} If `true`, runs `command` inside of a shell. Uses
`'/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).
* `windowsVerbatimArguments` {boolean} No quoting or escaping of arguments is
done on Windows. Ignored on Unix. This is set to `true` automatically
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 child process using an
AbortSignal.
* `timeout` {number} In milliseconds the maximum amount of time the process
is allowed to run. **Default:** `undefined`.
* `killSignal` {string|integer} The signal value to be used when the spawned
process will be killed by timeout or abort signal. **Default:** `'SIGTERM'`.
* Returns: {ChildProcess}
The `child_process.spawn()` method spawns a new process using the given
`command`, with command-line arguments in `args`. If omitted, `args` defaults
to an empty array.
**If the `shell` option is enabled, do not pass unsanitized user input to this
function. Any input containing shell metacharacters may be used to trigger
arbitrary command execution.**
A third argument may be used to specify additional options, with these defaults:
```js
const defaults = {
cwd: undefined,
env: process.env
};
```
Use `cwd` to specify the working directory from which the process is spawned.
If not given, the default is to inherit the current working directory. If given,
but the path does not exist, the child process emits an `ENOENT` error
and exits immediately. `ENOENT` is also emitted when the command
does not exist.
Use `env` to specify environment variables that will be visible to the new
process, the default is [`process.env`][].
`undefined` values in `env` will be ignored.
Example of running `ls -lh /usr`, capturing `stdout`, `stderr`, and the
exit code:
```js
const { spawn } = require('child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.error(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
```
Example: A very elaborate way to run `ps ax | grep ssh`
```js
const { spawn } = require('child_process');
const ps = spawn('ps', ['ax']);
const grep = spawn('grep', ['ssh']);
ps.stdout.on('data', (data) => {
grep.stdin.write(data);
});
ps.stderr.on('data', (data) => {
console.error(`ps stderr: ${data}`);
});
ps.on('close', (code) => {
if (code !== 0) {
console.log(`ps process exited with code ${code}`);
}
grep.stdin.end();
});
grep.stdout.on('data', (data) => {
console.log(data.toString());
});
grep.stderr.on('data', (data) => {
console.error(`grep stderr: ${data}`);
});
grep.on('close', (code) => {
if (code !== 0) {
console.log(`grep process exited with code ${code}`);
}
});
```
Example of checking for failed `spawn`:
```js
const { spawn } = require('child_process');
const subprocess = spawn('bad_command');
subprocess.on('error', (err) => {
console.error('Failed to start subprocess.');
});
```
Certain platforms (macOS, Linux) will use the value of `argv[0]` for the process
title while others (Windows, SunOS) will use `command`.
Node.js currently overwrites `argv[0]` with `process.execPath` on startup, so
`process.argv[0]` in a Node.js child process will not match the `argv0`
parameter passed to `spawn` from the parent, retrieve it with the
`process.argv0` property instead.
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 { 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 child process
```
#### `options.detached`
<!-- YAML
added: v0.7.10
-->
On Windows, setting `options.detached` to `true` makes it possible for the
child process to continue running after the parent exits. The child will have
its own console window. Once enabled for a child process, it cannot be
disabled.
On non-Windows platforms, if `options.detached` is set to `true`, the child
process will be made the leader of a new process group and session. Child
processes may continue running after the parent exits regardless of whether
they are detached or not. See setsid(2) for more information.
By default, the parent will wait for the detached child to exit. To prevent the
parent from waiting for a given `subprocess` to exit, use the
`subprocess.unref()` method. Doing so will cause the parent's event loop to not
include the child in its reference count, allowing the parent to exit
independently of the child, unless there is an established IPC channel between
the child and the parent.
When using the `detached` option to start a long-running process, the process
will not stay running in the background after the parent exits unless it is
provided with a `stdio` configuration that is not connected to the parent.
If the parent's `stdio` is inherited, the child will remain attached to the
controlling terminal.
Example of a long-running process, by detaching and also ignoring its parent
`stdio` file descriptors, in order to ignore the parent's termination:
```js
const { spawn } = require('child_process');
const subprocess = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
subprocess.unref();
```
Alternatively one can redirect the child process' output into files:
```js
const fs = require('fs');
const { spawn } = require('child_process');
const out = fs.openSync('./out.log', 'a');
const err = fs.openSync('./out.log', 'a');
const subprocess = spawn('prg', [], {
detached: true,
stdio: [ 'ignore', out, err ]
});
subprocess.unref();
```
#### `options.stdio`
<!-- YAML
added: v0.7.10
changes:
- version:
- v15.6.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/29412
description: Added the `overlapped` stdio flag.
- version: v3.3.1
pr-url: https://github.com/nodejs/node/pull/2727
description: The value `0` is now accepted as a file descriptor.
-->
The `options.stdio` option is used to configure the pipes that are established
between the parent and child process. By default, the child's stdin, stdout,
and stderr are redirected to corresponding [`subprocess.stdin`][],
[`subprocess.stdout`][], and [`subprocess.stderr`][] streams on the
[`ChildProcess`][] object. This is equivalent to setting the `options.stdio`
equal to `['pipe', 'pipe', 'pipe']`.
For convenience, `options.stdio` may be one of the following strings:
* `'pipe'`: equivalent to `['pipe', 'pipe', 'pipe']` (the default)
* `'overlapped'`: equivalent to `['overlapped', 'overlapped', 'overlapped']`
* `'ignore'`: equivalent to `['ignore', 'ignore', 'ignore']`
* `'inherit'`: equivalent to `['inherit', 'inherit', 'inherit']` or `[0, 1, 2]`
Otherwise, the value of `options.stdio` is an array where each index corresponds
to an fd in the child. The fds 0, 1, and 2 correspond to stdin, stdout,
and stderr, respectively. Additional fds can be specified to create additional
pipes between the parent and child. The value is one of the following:
1. `'pipe'`: Create a pipe between the child process and the parent process.
The parent end of the pipe is exposed to the parent as a property on the
`child_process` object as [`subprocess.stdio[fd]`][`subprocess.stdio`]. Pipes
created for fds 0, 1, and 2 are also available as [`subprocess.stdin`][],
[`subprocess.stdout`][] and [`subprocess.stderr`][], respectively.
1. `'overlapped'`: Same as `'pipe'` except that the `FILE_FLAG_OVERLAPPED` flag
is set on the handle. This is necessary for overlapped I/O on the child
process's stdio handles. See the
[docs](https://docs.microsoft.com/en-us/windows/win32/fileio/synchronous-and-asynchronous-i-o)
for more details. This is exactly the same as `'pipe'` on non-Windows
systems.
1. `'ipc'`: Create an IPC channel for passing messages/file descriptors
between parent and child. A [`ChildProcess`][] may have at most one IPC
stdio file descriptor. Setting this option enables the
[`subprocess.send()`][] method. If the child is a Node.js process, the
presence of an IPC channel will enable [`process.send()`][] and
[`process.disconnect()`][] methods, as well as [`'disconnect'`][] and
[`'message'`][] events within the child.
Accessing the IPC channel fd in any way other than [`process.send()`][]
or using the IPC channel with a child process that is not a Node.js instance
is not supported.
1. `'ignore'`: Instructs Node.js to ignore the fd in the child. While Node.js
will always open fds 0, 1, and 2 for the processes it spawns, setting the fd
to `'ignore'` will cause Node.js to open `/dev/null` and attach it to the
child's fd.
1. `'inherit'`: Pass through the corresponding stdio stream to/from the
parent process. In the first three positions, this is equivalent to
`process.stdin`, `process.stdout`, and `process.stderr`, respectively. In
any other position, equivalent to `'ignore'`.
1. {Stream} object: Share a readable or writable stream that refers to a tty,
file, socket, or a pipe with the child process. The stream's underlying
file descriptor is duplicated in the child process to the fd that
corresponds to the index in the `stdio` array. The stream must have an
underlying descriptor (file streams do not until the `'open'` event has
occurred).
1. Positive integer: The integer value is interpreted as a file descriptor
that is currently open in the parent process. It is shared with the child
process, similar to how {Stream} objects can be shared. Passing sockets
is not supported on Windows.
1. `null`, `undefined`: Use default value. For stdio fds 0, 1, and 2 (in other
words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the
default is `'ignore'`.
```js
const { spawn } = require('child_process');
// Child will use parent's stdios.
spawn('prg', [], { stdio: 'inherit' });
// Spawn child sharing only stderr.
spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });
// Open an extra fd=4, to interact with programs presenting a
// startd-style interface.
spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });
```
*It is worth noting that when an IPC channel is established between the
parent and child processes, and the child is a Node.js process, the child
is launched with the IPC channel unreferenced (using `unref()`) until the
child registers an event handler for the [`'disconnect'`][] event
or the [`'message'`][] event. This allows the child to exit
normally without the process being held open by the open IPC channel.*
On Unix-like operating systems, the [`child_process.spawn()`][] method
performs memory operations synchronously before decoupling the event loop
from the child. Applications with a large memory footprint may find frequent
[`child_process.spawn()`][] calls to be a bottleneck. For more information,
see [V8 issue 7381](https://bugs.chromium.org/p/v8/issues/detail?id=7381).
See also: [`child_process.exec()`][] and [`child_process.fork()`][].
## Synchronous process creation
The [`child_process.spawnSync()`][], [`child_process.execSync()`][], and
[`child_process.execFileSync()`][] methods are synchronous and will block the
Node.js event loop, pausing execution of any additional code until the spawned
process exits.
Blocking calls like these are mostly useful for simplifying general-purpose
scripting tasks and for simplifying the loading/processing of application
configuration at startup.
### `child_process.execFileSync(file[, args][, options])`
<!-- YAML
added: v0.11.12
changes:
- version:
- v16.4.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/38862
description: The `cwd` option can be a WHATWG `URL` object using
`file:` protocol.
- version: v10.10.0
pr-url: https://github.com/nodejs/node/pull/22409
description: The `input` option can now be any `TypedArray` or a
`DataView`.
- version: v8.8.0
pr-url: https://github.com/nodejs/node/pull/15380
description: The `windowsHide` option is supported now.
- version: v8.0.0
pr-url: https://github.com/nodejs/node/pull/10653
description: The `input` option can now be a `Uint8Array`.
- version:
- v6.2.1
- v4.5.0
pr-url: https://github.com/nodejs/node/pull/6939
description: The `encoding` option can now explicitly be set to `buffer`.
-->
* `file` {string} The name or path of the executable file to run.
* `args` {string[]} List of string arguments.
* `options` {Object}
* `cwd` {string|URL} Current working directory of the child process.
* `input` {string|Buffer|TypedArray|DataView} The value which will be passed
as stdin to the spawned process. Supplying this value will override
`stdio[0]`.
* `stdio` {string|Array} Child's stdio configuration. `stderr` by default will
be output to the parent process' stderr unless `stdio` is specified.
**Default:** `'pipe'`.
* `env` {Object} Environment key-value pairs. **Default:** `process.env`.
* `uid` {number} Sets the user identity of the process (see setuid(2)).
* `gid` {number} Sets the group identity of the process (see setgid(2)).
* `timeout` {number} In milliseconds the maximum amount of time the process
is allowed to run. **Default:** `undefined`.
* `killSignal` {string|integer} The signal value to be used when the spawned
process will be killed. **Default:** `'SIGTERM'`.
* `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
stderr. If exceeded, the child process is terminated. See caveat at
[`maxBuffer` and Unicode][]. **Default:** `1024 * 1024`.
* `encoding` {string} The encoding used for all stdio inputs and outputs.
**Default:** `'buffer'`.
* `windowsHide` {boolean} Hide the subprocess console window that would
normally be created on Windows systems. **Default:** `false`.
* `shell` {boolean|string} If `true`, runs `command` inside of a shell. Uses
`'/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).
* Returns: {Buffer|string} The stdout from the command.
The `child_process.execFileSync()` method is generally identical to
[`child_process.execFile()`][] with the exception that the method will not
return until the child process has fully closed. When a timeout has been
encountered and `killSignal` is sent, the method won't return until the process
has completely exited.
If the child process intercepts and handles the `SIGTERM` signal and
does not exit, the parent process will still wait until the child process has
exited.
If the process times out or has a non-zero exit code, this method will throw an
[`Error`][] that will include the full result of the underlying
[`child_process.spawnSync()`][].
**If the `shell` option is enabled, do not pass unsanitized user input to this
function. Any input containing shell metacharacters may be used to trigger
arbitrary command execution.**
### `child_process.execSync(command[, options])`
<!-- YAML
added: v0.11.12
changes:
- version:
- v16.4.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/38862
description: The `cwd` option can be a WHATWG `URL` object using
`file:` protocol.
- version: v10.10.0
pr-url: https://github.com/nodejs/node/pull/22409
description: The `input` option can now be any `TypedArray` or a
`DataView`.
- version: v8.8.0
pr-url: https://github.com/nodejs/node/pull/15380
description: The `windowsHide` option is supported now.
- version: v8.0.0
pr-url: https://github.com/nodejs/node/pull/10653
description: The `input` option can now be a `Uint8Array`.
-->
* `command` {string} The command to run.
* `options` {Object}
* `cwd` {string|URL} Current working directory of the child process.
* `input` {string|Buffer|TypedArray|DataView} The value which will be passed
as stdin to the spawned process. Supplying this value will override
`stdio[0]`.
* `stdio` {string|Array} Child's stdio configuration. `stderr` by default will
be output to the parent process' stderr unless `stdio` is specified.
**Default:** `'pipe'`.
* `env` {Object} Environment key-value pairs. **Default:** `process.env`.
* `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.
* `uid` {number} Sets the user identity of the process. (See setuid(2)).
* `gid` {number} Sets the group identity of the process. (See setgid(2)).
* `timeout` {number} In milliseconds the maximum amount of time the process
is allowed to run. **Default:** `undefined`.
* `killSignal` {string|integer} The signal value to be used when the spawned
process will be killed. **Default:** `'SIGTERM'`.
* `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
stderr. If exceeded, the child process is terminated and any output is
truncated. See caveat at [`maxBuffer` and Unicode][].
**Default:** `1024 * 1024`.
* `encoding` {string} The encoding used for all stdio inputs and outputs.
**Default:** `'buffer'`.
* `windowsHide` {boolean} Hide the subprocess console window that would
normally be created on Windows systems. **Default:** `false`.
* Returns: {Buffer|string} The stdout from the command.
The `child_process.execSync()` method is generally identical to
[`child_process.exec()`][] with the exception that the method will not return
until the child process has fully closed. When a timeout has been encountered
and `killSignal` is sent, the method won't return until the process has
completely exited. If the child process intercepts and handles the `SIGTERM`
signal and doesn't exit, the parent process will wait until the child process
has exited.
If the process times out or has a non-zero exit code, this method will throw.
The [`Error`][] object will contain the entire result from
[`child_process.spawnSync()`][].
**Never pass unsanitized user input to this function. Any input containing shell
metacharacters may be used to trigger arbitrary command execution.**
### `child_process.spawnSync(command[, args][, options])`
<!-- YAML
added: v0.11.12
changes:
- version:
- v16.4.0
- v14.18.0
pr-url: https://github.com/nodejs/node/pull/38862
description: The `cwd` option can be a WHATWG `URL` object using
`file:` protocol.
- version: v10.10.0
pr-url: https://github.com/nodejs/node/pull/22409
description: The `input` option can now be any `TypedArray` or a
`DataView`.
- version: v8.8.0
pr-url: https://github.com/nodejs/node/pull/15380
description: The `windowsHide` option is supported now.
- version: v8.0.0
pr-url: https://github.com/nodejs/node/pull/10653
description: The `input` option can now be a `Uint8Array`.
- version:
- v6.2.1
- v4.5.0
pr-url: https://github.com/nodejs/node/pull/6939
description: The `encoding` option can now explicitly be set to `buffer`.
- version: v5.7.0
pr-url: https://github.com/nodejs/node/pull/4598
description: The `shell` option is supported now.
-->
* `command` {string} The command to run.
* `args` {string[]} List of string arguments.
* `options` {Object}
* `cwd` {string|URL} Current working directory of the child process.
* `input` {string|Buffer|TypedArray|DataView} The value which will be passed
as stdin to the spawned process. Supplying this value will override
`stdio[0]`.
* `argv0` {string} Explicitly set the value of `argv[0]` sent to the child
process. This will be set to `command` if not specified.
* `stdio` {string|Array} Child's stdio configuration.
* `env` {Object} Environment key-value pairs. **Default:** `process.env`.
* `uid` {number} Sets the user identity of the process (see setuid(2)).
* `gid` {number} Sets the group identity of the process (see setgid(2)).
* `timeout` {number} In milliseconds the maximum amount of time the process
is allowed to run. **Default:** `undefined`.
* `killSignal` {string|integer} The signal value to be used when the spawned
process will be killed. **Default:** `'SIGTERM'`.
* `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
stderr. If exceeded, the child process is terminated and any output is
truncated. See caveat at [`maxBuffer` and Unicode][].
**Default:** `1024 * 1024`.
* `encoding` {string} The encoding used for all stdio inputs and outputs.
**Default:** `'buffer'`.
* `shell` {boolean|string} If `true`, runs `command` inside of a shell. Uses
`'/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).
* `windowsVerbatimArguments` {boolean} No quoting or escaping of arguments is
done on Windows. Ignored on Unix. This is set to `true` automatically
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`.
* Returns: {Object}
* `pid` {number} Pid of the child process.
* `output` {Array} Array of results from stdio output.
* `stdout` {Buffer|string} The contents of `output[1]`.
* `stderr` {Buffer|string} The contents of `output[2]`.
* `status` {number|null} The exit code of the subprocess, or `null` if the
subprocess terminated due to a signal.
* `signal` {string|null} The signal used to kill the subprocess, or `null` if
the subprocess did not terminate due to a signal.
* `error` {Error} The error object if the child process failed or timed out.
The `child_process.spawnSync()` method is generally identical to
[`child_process.spawn()`][] with the exception that the function will not return
until the child process has fully closed. When a timeout has been encountered
and `killSignal` is sent, the method won't return until the process has
completely exited. If the process intercepts and handles the `SIGTERM` signal
and doesn't exit, the parent process will wait until the child process has
exited.
**If the `shell` option is enabled, do not pass unsanitized user input to this
function. Any input containing shell metacharacters may be used to trigger
arbitrary command execution.**
## Class: `ChildProcess`
<!-- YAML
added: v2.2.0
-->
* Extends: {EventEmitter}
Instances of the `ChildProcess` represent spawned child processes.
Instances of `ChildProcess` are not intended to be created directly. Rather,
use the [`child_process.spawn()`][], [`child_process.exec()`][],
[`child_process.execFile()`][], or [`child_process.fork()`][] methods to create
instances of `ChildProcess`.
### Event: `'close'`
<!-- YAML
added: v0.7.7
-->
* `code` {number} The exit code if the child exited on its own.
* `signal` {string} The signal by which the child process was terminated.
The `'close'` event is emitted after a process has ended _and_ the stdio
streams of a child process have been closed. This is distinct from the
[`'exit'`][] event, since multiple processes might share the same stdio
streams. The `'close'` event will always emit after [`'exit'`][] was
already emitted, or [`'error'`][] if the child failed to spawn.
```js
const { spawn } = require('child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process close all stdio with code ${code}`);
});
ls.on('exit', (code) => {
console.log(`child process exited with code ${code}`);
});
```
### Event: `'disconnect'`
<!-- YAML
added: v0.7.2
-->
The `'disconnect'` event is emitted after calling the
[`subprocess.disconnect()`][] method in parent process or
[`process.disconnect()`][] in child process. After disconnecting it is no longer
possible to send or receive messages, and the [`subprocess.connected`][]
property is `false`.
### Event: `'error'`
* `err` {Error} The error.
The `'error'` event is emitted whenever:
1. The process could not be spawned, or
2. The process could not be killed, or
3. Sending a message to the child process failed.
The `'exit'` event may or may not fire after an error has occurred. When
listening to both the `'exit'` and `'error'` events, guard
against accidentally invoking handler functions multiple times.
See also [`subprocess.kill()`][] and [`subprocess.send()`][].
### Event: `'exit'`
<!-- YAML
added: v0.1.90
-->
* `code` {number} The exit code if the child exited on its own.
* `signal` {string} The signal by which the child process was terminated.
The `'exit'` event is emitted after the child process ends. If the process
exited, `code` is the final exit code of the process, otherwise `null`. If the
process terminated due to receipt of a signal, `signal` is the string name of
the signal, otherwise `null`. One of the two will always be non-`null`.
When the `'exit'` event is triggered, child process stdio streams might still be
open.
Node.js establishes signal handlers for `SIGINT` and `SIGTERM` and Node.js
processes will not terminate immediately due to receipt of those signals.
Rather, Node.js will perform a sequence of cleanup actions and then will
re-raise the handled signal.
See waitpid(2).
### Event: `'message'`
<!-- YAML
added: v0.5.9
-->
* `message` {Object} A parsed JSON object or primitive value.
* `sendHandle` {Handle} A [`net.Socket`][] or [`net.Server`][] object, or
undefined.
The `'message'` event is triggered when a child process uses
[`process.send()`][] to send messages.
The message goes through serialization and parsing. The resulting
message might not be the same as what is originally sent.
If the `serialization` option was set to `'advanced'` used when spawning the
child process, the `message` argument can contain data that JSON is not able
to represent.
See [Advanced serialization][] for more details.
### Event: `'spawn'`
<!-- YAML
added:
- v15.1.0
- v14.17.0
-->
The `'spawn'` event is emitted once the child process has spawned successfully.
If the child process does not spawn successfully, the `'spawn'` event is not
emitted and the `'error'` event is emitted instead.
If emitted, the `'spawn'` event comes before all other events and before any
data is received via `stdout` or `stderr`.
The `'spawn'` event will fire regardless of whether an error occurs **within**
the spawned process. For example, if `bash some-command` spawns successfully,
the `'spawn'` event will fire, though `bash` may fail to spawn `some-command`.
This caveat also applies when using `{ shell: true }`.
### `subprocess.channel`
<!-- YAML
added: v7.1.0
changes:
- version: v14.0.0
pr-url: https://github.com/nodejs/node/pull/30165
description: The object no longer accidentally exposes native C++ bindings.
-->
* {Object} A pipe representing the IPC channel to the child process.
The `subprocess.channel` property is a reference to the child's IPC channel. If
no IPC channel currently exists, this property is `undefined`.
#### `subprocess.channel.ref()`
<!-- YAML
added: v7.1.0
-->
This method makes the IPC channel keep the event loop of the parent process
running if `.unref()` has been called before.
#### `subprocess.channel.unref()`
<!-- YAML
added: v7.1.0
-->
This method makes the IPC channel not keep the event loop of the parent process
running, and lets it finish even while the channel is open.
### `subprocess.connected`
<!-- YAML
added: v0.7.2
-->
* {boolean} Set to `false` after `subprocess.disconnect()` is called.
The `subprocess.connected` property indicates whether it is still possible to
send and receive messages from a child process. When `subprocess.connected` is
`false`, it is no longer possible to send or receive messages.
### `subprocess.disconnect()`
<!-- YAML
added: v0.7.2
-->
Closes the IPC channel between parent and child, allowing the child to exit
gracefully once there are no other connections keeping it alive. After calling
this method the `subprocess.connected` and `process.connected` properties in
both the parent and child (respectively) will be set to `false`, and it will be
no longer possible to pass messages between the processes.
The `'disconnect'` event will be emitted when there are no messages in the
process of being received. This will most often be triggered immediately after
calling `subprocess.disconnect()`.
When the child process is a Node.js instance (e.g. spawned using
[`child_process.fork()`][]), the `process.disconnect()` method can be invoked
within the child process to close the IPC channel as well.
### `subprocess.exitCode`
* {integer}
The `subprocess.exitCode` property indicates the exit code of the child process.
If the child process is still running, the field will be `null`.
### `subprocess.kill([signal])`
<!-- YAML
added: v0.1.90
-->
* `signal` {number|string}
* Returns: {boolean}
The `subprocess.kill()` method sends a signal to the child process. If no
argument is given, the process will be sent the `'SIGTERM'` signal. See
signal(7) for a list of available signals. This function returns `true` if
kill(2) succeeds, and `false` otherwise.
```js
const { spawn } = require('child_process');
const grep = spawn('grep', ['ssh']);
grep.on('close', (code, signal) => {
console.log(
`child process terminated due to receipt of signal ${signal}`);
});
// Send SIGHUP to process.
grep.kill('SIGHUP');
```
The [`ChildProcess`][] object may emit an [`'error'`][] event if the signal
cannot be delivered. Sending a signal to a child process that has already exited
is not an error but may have unforeseen consequences. Specifically, if the
process identifier (PID) has been reassigned to another process, the signal will
be delivered to that process instead which can have unexpected results.
While the function is called `kill`, the signal delivered to the child process
may not actually terminate the process.
See kill(2) for reference.
On Windows, where POSIX signals do not exist, the `signal` argument will be
ignored, and the process will be killed forcefully and abruptly (similar to
`'SIGKILL'`).
See [Signal Events][] for more details.
On Linux, child processes of child processes will not be terminated
when attempting to kill their parent. This is likely to happen when running a
new process in a shell or with the use of the `shell` option of `ChildProcess`:
```js
'use strict';
const { spawn } = require('child_process');
const subprocess = spawn(
'sh',
[
'-c',
`node -e "setInterval(() => {
console.log(process.pid, 'is alive')
}, 500);"`,
], {
stdio: ['inherit', 'inherit', 'inherit']
}
);
setTimeout(() => {
subprocess.kill(); // Does not terminate the Node.js process in the shell.
}, 2000);
```
### `subprocess.killed`
<!-- YAML
added: v0.5.10
-->
* {boolean} Set to `true` after `subprocess.kill()` is used to successfully
send a signal to the child process.
The `subprocess.killed` property indicates whether the child process
successfully received a signal from `subprocess.kill()`. The `killed` property
does not indicate that the child process has been terminated.
### `subprocess.pid`
<!-- YAML
added: v0.1.90
-->
* {integer|undefined}
Returns the process identifier (PID) of the child process. If the child process
fails to spawn due to errors, then the value is `undefined` and `error` is
emitted.
```js
const { spawn } = require('child_process');
const grep = spawn('grep', ['ssh']);
console.log(`Spawned child pid: ${grep.pid}`);
grep.stdin.end();
```
### `subprocess.ref()`
<!-- YAML
added: v0.7.10
-->
Calling `subprocess.ref()` after making a call to `subprocess.unref()` will
restore the removed reference count for the child process, forcing the parent
to wait for the child to exit before exiting itself.
```js
const { spawn } = require('child_process');
const subprocess = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
subprocess.unref();
subprocess.ref();
```
### `subprocess.send(message[, sendHandle[, options]][, callback])`
<!-- YAML
added: v0.5.9
changes:
- version: v5.8.0
pr-url: https://github.com/nodejs/node/pull/5283
description: The `options` parameter, and the `keepOpen` option
in particular, is supported now.
- version: v5.0.0
pr-url: https://github.com/nodejs/node/pull/3516
description: This method returns a boolean for flow control now.
- version: v4.0.0
pr-url: https://github.com/nodejs/node/pull/2620
description: The `callback` parameter is supported now.
-->
* `message` {Object}
* `sendHandle` {Handle}
* `options` {Object} The `options` argument, if present, is an object used to
parameterize the sending of certain types of handles. `options` supports
the following properties:
* `keepOpen` {boolean} A value that can be used when passing instances of
`net.Socket`. When `true`, the socket is kept open in the sending process.
**Default:** `false`.
* `callback` {Function}
* Returns: {boolean}
When an IPC channel has been established between the parent and child (
i.e. when using [`child_process.fork()`][]), the `subprocess.send()` method can
be used to send messages to the child process. When the child process is a
Node.js instance, these messages can be received via the [`'message'`][] event.
The message goes through serialization and parsing. The resulting
message might not be the same as what is originally sent.
For example, in the parent script:
```js
const cp = require('child_process');
const n = cp.fork(`${__dirname}/sub.js`);
n.on('message', (m) => {
console.log('PARENT got message:', m);
});
// Causes the child to print: CHILD got message: { hello: 'world' }
n.send({ hello: 'world' });
```
And then the child script, `'sub.js'` might look like this:
```js
process.on('message', (m) => {
console.log('CHILD got message:', m);
});
// Causes the parent to print: PARENT got message: { foo: 'bar', baz: null }
process.send({ foo: 'bar', baz: NaN });
```
Child Node.js processes will have a [`process.send()`][] method of their own
that allows the child to send messages back to the parent.
There is a special case when sending a `{cmd: 'NODE_foo'}` message. Messages
containing a `NODE_` prefix in the `cmd` property are reserved for use within
Node.js core and will not be emitted in the child's [`'message'`][]
event. Rather, such messages are emitted using the
`'internalMessage'` event and are consumed internally by Node.js.
Applications should avoid using such messages or listening for
`'internalMessage'` events as it is subject to change without notice.
The optional `sendHandle` argument that may be passed to `subprocess.send()` is
for passing a TCP server or socket object to the child process. The child will
receive the object as the second argument passed to the callback function
registered on the [`'message'`][] event. Any data that is received
and buffered in the socket will not be sent to the child.
The optional `callback` is a function that is invoked after the message is
sent but before the child may have received it. The function is called with a
single argument: `null` on success, or an [`Error`][] object on failure.
If no `callback` function is provided and the message cannot be sent, an
`'error'` event will be emitted by the [`ChildProcess`][] object. This can
happen, for instance, when the child process has already exited.
`subprocess.send()` will return `false` if the channel has closed or when the
backlog of unsent messages exceeds a threshold that makes it unwise to send
more. Otherwise, the method returns `true`. The `callback` function can be
used to implement flow control.
#### Example: sending a server object
The `sendHandle` argument can be used, for instance, to pass the handle of
a TCP server object to the child process as illustrated in the example below:
```js
const subprocess = require('child_process').fork('subprocess.js');
// Open up the server object and send the handle.
const server = require('net').createServer();
server.on('connection', (socket) => {
socket.end('handled by parent');
});
server.listen(1337, () => {
subprocess.send('server', server);
});
```
The child would then receive the server object as:
```js
process.on('message', (m, server) => {
if (m === 'server') {
server.on('connection', (socket) => {
socket.end('handled by child');
});
}
});
```
Once the server is now shared between the parent and child, some connections
can be handled by the parent and some by the child.
While the example above uses a server created using the `net` module, `dgram`
module servers use exactly the same workflow with the exceptions of listening on
a `'message'` event instead of `'connection'` and using `server.bind()` instead
of `server.listen()`. This is, however, currently only supported on Unix
platforms.
#### Example: sending a socket object
Similarly, the `sendHandler` argument can be used to pass the handle of a
socket to the child process. The example below spawns two children that each
handle connections with "normal" or "special" priority:
```js
const { fork } = require('child_process');
const normal = fork('subprocess.js', ['normal']);
const special = fork('subprocess.js', ['special']);
// Open up the server and send sockets to child. Use pauseOnConnect to prevent
// the sockets from being read before they are sent to the child process.
const server = require('net').createServer({ pauseOnConnect: true });
server.on('connection', (socket) => {
// If this is special priority...
if (socket.remoteAddress === '74.125.127.100') {
special.send('socket', socket);
return;
}
// This is normal priority.
normal.send('socket', socket);
});
server.listen(1337);
```
The `subprocess.js` would receive the socket handle as the second argument
passed to the event callback function:
```js
process.on('message', (m, socket) => {
if (m === 'socket') {
if (socket) {
// Check that the client socket exists.
// It is possible for the socket to be closed between the time it is
// sent and the time it is received in the child process.
socket.end(`Request handled with ${process.argv[2]} priority`);
}
}
});
```
Do not use `.maxConnections` on a socket that has been passed to a subprocess.
The parent cannot track when the socket is destroyed.
Any `'message'` handlers in the subprocess should verify that `socket` exists,
as the connection may have been closed during the time it takes to send the
connection to the child.
### `subprocess.signalCode`
* {string|null}
The `subprocess.signalCode` property indicates the signal received by
the child process if any, else `null`.
### `subprocess.spawnargs`
* {Array}
The `subprocess.spawnargs` property represents the full list of command-line
arguments the child process was launched with.
### `subprocess.spawnfile`
* {string}
The `subprocess.spawnfile` property indicates the executable file name of
the child process that is launched.
For [`child_process.fork()`][], its value will be equal to
[`process.execPath`][].
For [`child_process.spawn()`][], its value will be the name of
the executable file.
For [`child_process.exec()`][], its value will be the name of the shell
in which the child process is launched.
### `subprocess.stderr`
<!-- YAML
added: v0.1.90
-->
* {stream.Readable}
A `Readable Stream` that represents the child process's `stderr`.
If the child was spawned with `stdio[2]` set to anything other than `'pipe'`,
then this will be `null`.
`subprocess.stderr` is an alias for `subprocess.stdio[2]`. Both properties will
refer to the same value.
The `subprocess.stderr` property can be `null` if the child process could
not be successfully spawned.
### `subprocess.stdin`
<!-- YAML
added: v0.1.90
-->
* {stream.Writable}
A `Writable Stream` that represents the child process's `stdin`.
If a child process waits to read all of its input, the child will not continue
until this stream has been closed via `end()`.
If the child was spawned with `stdio[0]` set to anything other than `'pipe'`,
then this will be `null`.
`subprocess.stdin` is an alias for `subprocess.stdio[0]`. Both properties will
refer to the same value.
The `subprocess.stdin` property can be `undefined` if the child process could
not be successfully spawned.
### `subprocess.stdio`
<!-- YAML
added: v0.7.10
-->
* {Array}
A sparse array of pipes to the child process, corresponding with positions in
the [`stdio`][] option passed to [`child_process.spawn()`][] that have been set
to the value `'pipe'`. `subprocess.stdio[0]`, `subprocess.stdio[1]`, and
`subprocess.stdio[2]` are also available as `subprocess.stdin`,
`subprocess.stdout`, and `subprocess.stderr`, respectively.
In the following example, only the child's fd `1` (stdout) is configured as a
pipe, so only the parent's `subprocess.stdio[1]` is a stream, all other values
in the array are `null`.
```js
const assert = require('assert');
const fs = require('fs');
const child_process = require('child_process');
const subprocess = child_process.spawn('ls', {
stdio: [
0, // Use parent's stdin for child.
'pipe', // Pipe child's stdout to parent.
fs.openSync('err.out', 'w'), // Direct child's stderr to a file.
]
});
assert.strictEqual(subprocess.stdio[0], null);
assert.strictEqual(subprocess.stdio[0], subprocess.stdin);
assert(subprocess.stdout);
assert.strictEqual(subprocess.stdio[1], subprocess.stdout);
assert.strictEqual(subprocess.stdio[2], null);
assert.strictEqual(subprocess.stdio[2], subprocess.stderr);
```
The `subprocess.stdio` property can be `undefined` if the child process could
not be successfully spawned.
### `subprocess.stdout`
<!-- YAML
added: v0.1.90
-->
* {stream.Readable}
A `Readable Stream` that represents the child process's `stdout`.
If the child was spawned with `stdio[1]` set to anything other than `'pipe'`,
then this will be `null`.
`subprocess.stdout` is an alias for `subprocess.stdio[1]`. Both properties will
refer to the same value.
```js
const { spawn } = require('child_process');
const subprocess = spawn('ls');
subprocess.stdout.on('data', (data) => {
console.log(`Received chunk ${data}`);
});
```
The `subprocess.stdout` property can be `null` if the child process could
not be successfully spawned.
### `subprocess.unref()`
<!-- YAML
added: v0.7.10
-->
By default, the parent will wait for the detached child to exit. To prevent the
parent from waiting for a given `subprocess` to exit, use the
`subprocess.unref()` method. Doing so will cause the parent's event loop to not
include the child in its reference count, allowing the parent to exit
independently of the child, unless there is an established IPC channel between
the child and the parent.
```js
const { spawn } = require('child_process');
const subprocess = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
subprocess.unref();
```
## `maxBuffer` and Unicode
The `maxBuffer` option specifies the largest number of bytes allowed on `stdout`
or `stderr`. If this value is exceeded, then the child process is terminated.
This impacts output that includes multibyte character encodings such as UTF-8 or
UTF-16. For instance, `console.log('中文测试')` will send 13 UTF-8 encoded bytes
to `stdout` although there are only 4 characters.
## Shell requirements
The shell should understand the `-c` switch. If the shell is `'cmd.exe'`, it
should understand the `/d /s /c` switches and command-line parsing should be
compatible.
## Default Windows shell
Although Microsoft specifies `%COMSPEC%` must contain the path to
`'cmd.exe'` in the root environment, child processes are not always subject to
the same requirement. Thus, in `child_process` functions where a shell can be
spawned, `'cmd.exe'` is used as a fallback if `process.env.ComSpec` is
unavailable.
## Advanced serialization
<!-- YAML
added:
- v13.2.0
- v12.16.0
-->
Child processes support a serialization mechanism for IPC that is based on the
[serialization API of the `v8` module][v8.serdes], based on the
[HTML structured clone algorithm][]. This is generally more powerful and
supports more built-in JavaScript object types, such as `BigInt`, `Map`
and `Set`, `ArrayBuffer` and `TypedArray`, `Buffer`, `Error`, `RegExp` etc.
However, this format is not a full superset of JSON, and e.g. properties set on
objects of such built-in types will not be passed on through the serialization
step. Additionally, performance may not be equivalent to that of JSON, depending
on the structure of the passed data.
Therefore, this feature requires opting in by setting the
`serialization` option to `'advanced'` when calling [`child_process.spawn()`][]
or [`child_process.fork()`][].
[Advanced serialization]: #advanced-serialization
[Default Windows shell]: #default-windows-shell
[HTML structured clone algorithm]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
[Shell requirements]: #shell-requirements
[Signal Events]: process.md#signal-events
[`'disconnect'`]: process.md#event-disconnect
[`'error'`]: #event-error
[`'exit'`]: #event-exit
[`'message'`]: process.md#event-message
[`ChildProcess`]: #class-childprocess
[`Error`]: errors.md#class-error
[`EventEmitter`]: events.md#class-eventemitter
[`child_process.exec()`]: #child_processexeccommand-options-callback
[`child_process.execFile()`]: #child_processexecfilefile-args-options-callback
[`child_process.execFileSync()`]: #child_processexecfilesyncfile-args-options
[`child_process.execSync()`]: #child_processexecsynccommand-options
[`child_process.fork()`]: #child_processforkmodulepath-args-options
[`child_process.spawn()`]: #child_processspawncommand-args-options
[`child_process.spawnSync()`]: #child_processspawnsynccommand-args-options
[`maxBuffer` and Unicode]: #maxbuffer-and-unicode
[`net.Server`]: net.md#class-netserver
[`net.Socket`]: net.md#class-netsocket
[`options.detached`]: #optionsdetached
[`process.disconnect()`]: process.md#processdisconnect
[`process.env`]: process.md#processenv
[`process.execPath`]: process.md#processexecpath
[`process.send()`]: process.md#processsendmessage-sendhandle-options-callback
[`stdio`]: #optionsstdio
[`subprocess.connected`]: #subprocessconnected
[`subprocess.disconnect()`]: #subprocessdisconnect
[`subprocess.kill()`]: #subprocesskillsignal
[`subprocess.send()`]: #subprocesssendmessage-sendhandle-options-callback
[`subprocess.stderr`]: #subprocessstderr
[`subprocess.stdin`]: #subprocessstdin
[`subprocess.stdio`]: #subprocessstdio
[`subprocess.stdout`]: #subprocessstdout
[`util.promisify()`]: util.md#utilpromisifyoriginal
[synchronous counterparts]: #synchronous-process-creation
[v8.serdes]: v8.md#serialization-api
|