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If in a terminal I run git flow release publish '1.0.0' it is executed successfully.
If I use child_process.spawn in a test.js and then run it with node ./test.js file it also works fine.
But when I use child_process.spawn inside VS Code extension it produces error
fatal: could not read Username for 'https://github.com': No such device or address
If I edit .git/config and add my name https//$myname#github.com...... then error is
fatal: could not read Password for 'https://github.com': No such device or address.
Here is my code same in test file and VS Code
const spawn = require("child_process").spawn;
let cmd = 'git';
let args = ['flow', 'release', 'publish', '0.2.8'];
// let args = ['flow', 'release', 'delete', '-f', '-r', '0.2.8'];
const child = spawn(cmd, args);
let stdout = [];
let stderr = [];
child.stdout?.on('data', (data) => {
console.log(`[gitflow] Stdout ${data}`);
stdout.push(data.toString());
});
child.stderr?.on('data', (data) => {
console.log(`[gitflow] Stderr ${data}`);
stderr.push(data.toString());
});
child.on('error', err => {
console.log(`[gitflow] Error "${cmd} ${args?.join(" ")}" returned`, err);
});
child.on('spawm', err => {
console.log(`[gitflow] Spawn "${cmd} ${args?.join(" ")}" returned`, err);
});
child.on('exit', code => {
console.log(`[gitflow] Exit "${cmd} ${args?.join(" ")} exited`, code);
});
child.on('close', retc => {
console.log(`[gitflow] Command "${cmd}"`, retc, stderr, stdout);
});
I'm not sure this is a bug or feature, but when killing a shell (using kill -9 <pid>) it doesn't exit the process, as in it calls the exit event but all code continues running. Here is my code
// index.js
const { spawn } = require("child_process");
const deploy = spawn(`node server`, {
shell: true,
});
console.log(deploy.pid); // I use this to get the PID so i can use the kill command
deploy.stdout.on("data", (data) => {
console.log(data.toString());
});
deploy.stderr.on("data", (data) => {
console.log(data.toString());
});
deploy.on("exit", (code) => {
console.log("exit");
});
// server.js
const app = require("express")();
app.use("/", (req, res) => {
console.log("debug");
res.send("Hello, World");
});
app.listen(8000, () => console.log("Site Online"));
According to the documents, using the sh command on Linux with the -c flag, 1) Fixes the problem of it not closing, 2) Allows you to run multiple commands without the shell option that causes the problem in the first place.
Example:
const deploy = spawn("sh", ["-c", `node server && ls`], {
stdio: ["inherit", "inherit", "inherit"],
});
I want to use child_process.spawn to execute a windows exe file and catch it's output.
When I use command line to run a thirdparty exe file (says A.exe), it will print some logs to the cmd window. Like this:
C:\> A.exe
some outputs...
some more outputs...
However, when I spawn it in node.js, using this
import childProcess from 'child_process';
const cp = childProcess.spawn('A.exe');
cp.stdout.on('data', data => console.log(`stdout: ${data}`));
cp.stderr.on('data', data => console.log(`stderr: ${data}`));
There is no outputs at all.
I think the outputs of A.exe is not to the stdout (so I can never get data by listening stdout), but I don't know how it print logs when running from command line.
Any help would be greatly appreciated.
On Unix-type operating systems (Unix, Linux, macOS) child_process.execFile() can be more efficient because it does not spawn a shell. 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.
// 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.log(data.toString());
});
bat.on('exit', (code) => {
console.log(`Child exited with code ${code}`);
});
Maybe give this approach a go:
var childProcess = require('child_process');
childProcess.exec('A.exe', function(error, stdout, stderr) {
if (error != null) {
console.log('error occurred: ' + error);
} else {
console.log('stdout: ' + stdout);
console.log('stderr: ' + stderr);
}
});
// OR
var cp = childProcess.spawn('A.exe');
cp.stdout.on('data', (data) => {
console.log('stdout: ' + data.toString());
});
cp.stderr.on('data', (data) => {
console.log('stderr: ' + data.toString());
});
I have a script that outputs 'hi', sleeps for a second, outputs 'hi', sleeps for 1 second, and so on and so forth. Now I thought I would be able to tackle this problem with this model.
var spawn = require('child_process').spawn,
temp = spawn('PATH TO SCRIPT WITH THE ABOVE BEHAVIOUR');
temp.stdout.pipe(process.stdout);
Now the problem is that the task needs to be finished in order for the output to be displayed. As I am understanding it, this is due to the fact that the newly spawned process takes execution control. Obviously node.js does not support threads so any solutions? My idea was to possibly run two instances, first one for the specific purpose of creating the task and have it pipe the output to process of the second instance, considering this can be achieved.
It's much easier now (6 years later)!
Spawn returns a childObject, which you can then listen for events with. The events are:
Class: ChildProcess
Event: 'error'
Event: 'exit'
Event: 'close'
Event: 'disconnect'
Event: 'message'
There are also a bunch of objects from childObject, they are:
Class: ChildProcess
child.stdin
child.stdout
child.stderr
child.stdio
child.pid
child.connected
child.kill([signal])
child.send(message[, sendHandle][, callback])
child.disconnect()
See more information here about childObject: https://nodejs.org/api/child_process.html
Asynchronous
If you want to run your process in the background while node is still able to continue to execute, use the asynchronous method. You can still choose to perform actions after your process completes, and when the process has any output (for example if you want to send a script's output to the client).
child_process.spawn(...); (Node v0.1.90)
var spawn = require('child_process').spawn;
var child = spawn('node ./commands/server.js');
// You can also use a variable to save the output
// for when the script closes later
var scriptOutput = "";
child.stdout.setEncoding('utf8');
child.stdout.on('data', function(data) {
//Here is where the output goes
console.log('stdout: ' + data);
data=data.toString();
scriptOutput+=data;
});
child.stderr.setEncoding('utf8');
child.stderr.on('data', function(data) {
//Here is where the error output goes
console.log('stderr: ' + data);
data=data.toString();
scriptOutput+=data;
});
child.on('close', function(code) {
//Here you can get the exit code of the script
console.log('closing code: ' + code);
console.log('Full output of script: ',scriptOutput);
});
Here's how you would use a callback + asynchronous method:
var child_process = require('child_process');
console.log("Node Version: ", process.version);
run_script("ls", ["-l", "/home"], function(output, exit_code) {
console.log("Process Finished.");
console.log('closing code: ' + exit_code);
console.log('Full output of script: ',output);
});
console.log ("Continuing to do node things while the process runs at the same time...");
// This function will output the lines from the script
// AS is runs, AND will return the full combined output
// as well as exit code when it's done (using the callback).
function run_script(command, args, callback) {
console.log("Starting Process.");
var child = child_process.spawn(command, args);
var scriptOutput = "";
child.stdout.setEncoding('utf8');
child.stdout.on('data', function(data) {
console.log('stdout: ' + data);
data=data.toString();
scriptOutput+=data;
});
child.stderr.setEncoding('utf8');
child.stderr.on('data', function(data) {
console.log('stderr: ' + data);
data=data.toString();
scriptOutput+=data;
});
child.on('close', function(code) {
callback(scriptOutput,code);
});
}
Using the method above, you can send every line of output from the script to the client (for example using Socket.io to send each line when you receive events on stdout or stderr).
Synchronous
If you want node to stop what it's doing and wait until the script completes, you can use the synchronous version:
child_process.spawnSync(...); (Node v0.11.12+)
Issues with this method:
If the script takes a while to complete, your server will hang for
that amount of time!
The stdout will only be returned once the script
has finished running. Because it's synchronous, it cannot continue
until the current line has finished. Therefore it's unable to capture
the 'stdout' event until the spawn line has finished.
How to use it:
var child_process = require('child_process');
var child = child_process.spawnSync("ls", ["-l", "/home"], { encoding : 'utf8' });
console.log("Process finished.");
if(child.error) {
console.log("ERROR: ",child.error);
}
console.log("stdout: ",child.stdout);
console.log("stderr: ",child.stderr);
console.log("exist code: ",child.status);
I'm still getting my feet wet with Node.js, but I have a few ideas. first, I believe you need to use execFile instead of spawn; execFile is for when you have the path to a script, whereas spawn is for executing a well-known command that Node.js can resolve against your system path.
1. Provide a callback to process the buffered output:
var child = require('child_process').execFile('path/to/script', [
'arg1', 'arg2', 'arg3',
], function(err, stdout, stderr) {
// Node.js will invoke this callback when process terminates.
console.log(stdout);
});
2. Add a listener to the child process' stdout stream (9thport.net)
var child = require('child_process').execFile('path/to/script', [
'arg1', 'arg2', 'arg3' ]);
// use event hooks to provide a callback to execute when data are available:
child.stdout.on('data', function(data) {
console.log(data.toString());
});
Further, there appear to be options whereby you can detach the spawned process from Node's controlling terminal, which would allow it to run asynchronously. I haven't tested this yet, but there are examples in the API docs that go something like this:
child = require('child_process').execFile('path/to/script', [
'arg1', 'arg2', 'arg3',
], {
// detachment and ignored stdin are the key here:
detached: true,
stdio: [ 'ignore', 1, 2 ]
});
// and unref() somehow disentangles the child's event loop from the parent's:
child.unref();
child.stdout.on('data', function(data) {
console.log(data.toString());
});
Here is the cleanest approach I've found:
require("child_process").spawn('bash', ['./script.sh'], {
cwd: process.cwd(),
detached: true,
stdio: "inherit"
});
I had a little trouble getting logging output from the "npm install" command when I spawned npm in a child process. The realtime logging of dependencies did not show in the parent console.
The simplest way to do what the original poster wants seems to be this (spawn npm on windows and log everything to parent console):
var args = ['install'];
var options = {
stdio: 'inherit' //feed all child process logging into parent process
};
var childProcess = spawn('npm.cmd', args, options);
childProcess.on('close', function(code) {
process.stdout.write('"npm install" finished with code ' + code + '\n');
});
PHP-like passthru
import { spawn } from 'child_process';
export default async function passthru(exe, args, options) {
return new Promise((resolve, reject) => {
const env = Object.create(process.env);
const child = spawn(exe, args, {
...options,
env: {
...env,
...options.env,
},
});
child.stdout.setEncoding('utf8');
child.stderr.setEncoding('utf8');
child.stdout.on('data', data => console.log(data));
child.stderr.on('data', data => console.log(data));
child.on('error', error => reject(error));
child.on('close', exitCode => {
console.log('Exit code:', exitCode);
resolve(exitCode);
});
});
}
Usage
const exitCode = await passthru('ls', ['-al'], { cwd: '/var/www/html' })
child:
setInterval(function() {
process.stdout.write("hi");
}, 1000); // or however else you want to run a timer
parent:
require('child_process').fork('./childfile.js');
// fork'd children use the parent's stdio
I found myself requiring this functionality often enough that I packaged it into a library called std-pour. It should let you execute a command and view the output in real time. To install simply:
npm install std-pour
Then it's simple enough to execute a command and see the output in realtime:
const { pour } = require('std-pour');
pour('ping', ['8.8.8.8', '-c', '4']).then(code => console.log(`Error Code: ${code}`));
It's promised based so you can chain multiple commands. It's even function signature-compatible with child_process.spawn so it should be a drop in replacement anywhere you're using it.
Adding a sample for exec as I too had needed live feedback and wasn't getting any until after the script finished. exec does return an EventEmitter, contrary to the many claims that only spawn works in such a way.
This supplements the comment I made to the accepted answer more thoroughly.
The interface for exec is similar to spawn:
// INCLUDES
import * as childProcess from 'child_process'; // ES6 Syntax
// DEFINES
let exec = childProcess.exec; // Use 'var' for more proper
// semantics, or 'const' it all
// if that's your thing; though 'let' is
// true-to-scope;
// Return an EventEmitter to work with, though
// you can also chain stdout too:
// (i.e. exec( ... ).stdout.on( ... ); )
let childProcess = exec
(
'./binary command -- --argument argumentValue',
( error, stdout, stderr ) =>
{ // When the process completes:
if( error )
{
console.log( `${error.name}: ${error.message}` );
console.log( `[STACK] ${error.stack}` );
}
console.log( stdout );
console.log( stderr );
callback(); // Gulp stuff
}
);
Now its as simple as registering an event handler for stdout:
childProcess.stdout.on( 'data', data => console.log( data ) );
And for stderr:
childProcess.stderr.on( 'data', data => console.log( `[ERROR]: ${data}` ) );
You can also pipe stdout to the main process' stdout:
childProcess.stdout.pipe( process.stdout );
Not too bad at all - HTH
I was interested into running a script that gets the input and outputs from my terminal, and that will close my process once the child script finishes.
import { spawn } from 'node:child_process'
import process from 'node:process'
const script = spawn('path/to/script', { stdio: 'inherit' })
script.on('close', process.exit)
I ran into a situation where none of the above worked when I was spawning a Python 3 script. I would get data from stdout, but only once the child terminated.
As it turns out, Python buffers stdout by default. It's possible to disable stdout buffering by including -u as a command line parameter to python3.
I have this simple script :
var exec = require('child_process').exec;
exec('coffee -cw my_file.coffee', function(error, stdout, stderr) {
console.log(stdout);
});
where I simply execute a command to compile a coffee-script file. But stdout never get displayed in the console, because the command never ends (because of the -w option of coffee).
If I execute the command directly from the console I get message like this :
18:05:59 - compiled my_file.coffee
My question is : is it possible to display these messages with the node.js exec ? If yes how ? !
Thanks
Don't use exec. Use spawn which is an EventEmmiter object. Then you can listen to stdout/stderr events (spawn.stdout.on('data',callback..)) as they happen.
From NodeJS documentation:
var spawn = require('child_process').spawn,
ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', function (data) {
console.log('stdout: ' + data.toString());
});
ls.stderr.on('data', function (data) {
console.log('stderr: ' + data.toString());
});
ls.on('exit', function (code) {
console.log('child process exited with code ' + code.toString());
});
exec buffers the output and usually returns it when the command has finished executing.
exec will also return a ChildProcess object that is an EventEmitter.
var exec = require('child_process').exec;
var coffeeProcess = exec('coffee -cw my_file.coffee');
coffeeProcess.stdout.on('data', function(data) {
console.log(data);
});
OR pipe the child process's stdout to the main stdout.
coffeeProcess.stdout.pipe(process.stdout);
OR inherit stdio using spawn
spawn('coffee -cw my_file.coffee', { stdio: 'inherit' });
There are already several answers however none of them mention the best (and easiest) way to do this, which is using spawn and the { stdio: 'inherit' } option. It seems to produce the most accurate output, for example when displaying the progress information from a git clone.
Simply do this:
var spawn = require('child_process').spawn;
spawn('coffee', ['-cw', 'my_file.coffee'], { stdio: 'inherit' });
Credit to #MorganTouvereyQuilling for pointing this out in this comment.
Inspired by Nathanael Smith's answer and Eric Freese's comment, it could be as simple as:
var exec = require('child_process').exec;
exec('coffee -cw my_file.coffee').stdout.pipe(process.stdout);
I'd just like to add that one small issue with outputting the buffer strings from a spawned process with console.log() is that it adds newlines, which can spread your spawned process output over additional lines. If you output stdout or stderr with process.stdout.write() instead of console.log(), then you'll get the console output from the spawned process 'as is'.
I saw that solution here:
Node.js: printing to console without a trailing newline?
Hope that helps someone using the solution above (which is a great one for live output, even if it is from the documentation).
I have found it helpful to add a custom exec script to my utilities that do this.
utilities.js
const { exec } = require('child_process')
module.exports.exec = (command) => {
const process = exec(command)
process.stdout.on('data', (data) => {
console.log('stdout: ' + data.toString())
})
process.stderr.on('data', (data) => {
console.log('stderr: ' + data.toString())
})
process.on('exit', (code) => {
console.log('child process exited with code ' + code.toString())
})
}
app.js
const { exec } = require('./utilities.js')
exec('coffee -cw my_file.coffee')
After reviewing all the other answers, I ended up with this:
function oldSchoolMakeBuild(cb) {
var makeProcess = exec('make -C ./oldSchoolMakeBuild',
function (error, stdout, stderr) {
stderr && console.error(stderr);
cb(error);
});
makeProcess.stdout.on('data', function(data) {
process.stdout.write('oldSchoolMakeBuild: '+ data);
});
}
Sometimes data will be multiple lines, so the oldSchoolMakeBuild header will appear once for multiple lines. But this didn't bother me enough to change it.
child_process.spawn returns an object with stdout and stderr streams.
You can tap on the stdout stream to read data that the child process sends back to Node. stdout being a stream has the "data", "end", and other events that streams have. spawn is best used to when you want the child process to return a large amount of data to Node - image processing, reading binary data etc.
so you can solve your problem using child_process.spawn as used below.
var spawn = require('child_process').spawn,
ls = spawn('coffee -cw my_file.coffee');
ls.stdout.on('data', function (data) {
console.log('stdout: ' + data.toString());
});
ls.stderr.on('data', function (data) {
console.log('stderr: ' + data.toString());
});
ls.on('exit', function (code) {
console.log('code ' + code.toString());
});
Here is an async helper function written in typescript that seems to do the trick for me. I guess this will not work for long-lived processes but still might be handy for someone?
import * as child_process from "child_process";
private async spawn(command: string, args: string[]): Promise<{code: number | null, result: string}> {
return new Promise((resolve, reject) => {
const spawn = child_process.spawn(command, args)
let result: string
spawn.stdout.on('data', (data: any) => {
if (result) {
reject(Error('Helper function does not work for long lived proccess'))
}
result = data.toString()
})
spawn.stderr.on('data', (error: any) => {
reject(Error(error.toString()))
})
spawn.on('exit', code => {
resolve({code, result})
})
})
}