preserve color when executing child_process.spawn

I'm trying to execute a windows command through cmd.exe in node.js using child_process.spawn. It executes correctly, but only displays in default text color. How do I preserver the color. Is it possible?

var spawn = require('child_process').spawn,
	cmd    = spawn('cmd', ['/s', '/c', 'C:\\Windows\\Microsoft.NET\\Framework\\v4.0.30319\\MSBuild c:\\test.sln']);

cmd.stdout.on('data', function(data){
	process.stdout.write(data);
});

cmd.stderr.on('data', function(data){
	process.stderr.write(data);
});

cmd.on('exit', function(code){
	console.log(code);
});

When executing via node, the color is not preserved.

When executing via cmd.exe directly, the color is present. (This is the expected behavior). How do I get this behvior when executing via node.

There are new 'stdio' option for child_process.spawn(). Try following:

spawn("path to executable", ["params"], {stdio: "inherit"});

"Inherit" means [0, 1, 2] or [process.stdin, process.stdout, process.stderr].

crossplatform solution that worked for me was to use both shell: true and stdio: 'inherit':

const spawn = require('child_process').spawn;

spawn('node', ['./child.js'], { shell: true, stdio: 'inherit' });

thanks @59naga https://github.com/nodejs/node/issues/2333

If you are getting error:

> Cannot call method 'on' of null

Try this:

spawn("command", ["args"], { env : { FORCE_COLOR: true }});

works with mocha

Try this instead:

var spawn = require('child_process').spawn
  , command = 'C:\\Windows\\Microsoft.NET\\Framework\\v4.0.30319\\MSBuild c:\\test.sln'
  , cmd    = spawn('cmd', ['/s', '/c', command], { customFds: [0,1,2] });

cmd.on('exit', function(code){
    console.log(code);
});

Note that I'm not positive whether or not customFds works on Windows. I know that it's old deprecated functionality doesn't work, but when only passing [0,1,2] as the fd's, I think there is a special case for that.

I've been doing something similar here, but I've only ran that command on Unix machines. So let me know if that works on Windows.

This doesn't fix the underlying issue (lack of a proper TTY stream) but it should help get around it.

If the sub-process you're running uses supports-color (https://www.npmjs.com/package/supports-color) like chalk, then you can set an environmental variable FORCE_COLOR to any value and it will skip the rest of the checks. This will allow you to continue to use pipes (and capture/modify the returned data) unlike the inherit fix.

There is also a node-pty (https://www.npmjs.com/package/node-pty) module that provides a .spawn with the ability to pass a pty (pseudo tty) that may be a more holistic answer. I haven't played with it yet, and I'm not sure if it's cross platform or not.

If you want to either keep the color or add some notation for the output, you can try the code below:

var spawn = require('child_process').spawn,
var stream = require('stream');
cmd = spawn('cmd', ['/s', '/c', 'C:\\Windows\\Microsoft.NET\\Framework\\v4.0.30319\\MSBuild c:\\test.sln'], { stdio: [process.stdin, process.stdout, 'pipe'] });
var customStream = new stream.Writable();
customStream._write = function (data, ...argv) {
        console.log('your notation');
        process.stderr._write(data, ...argv);
 };
cmd.stderr.pipe(customStream);

note that the code use es6

I have tried many options above, and they did not work. For npm (and probably node) commands, this works:

const ps = _spawn('npm', ['outdated', '--color=always'], { stdio: 'pipe'});
ps.stdout.pipe(process.stdout);
// Then, you can also ps.stdout.on('data',...) for further processing

The trick is the --color=always (using Mac OSX with zsh). I did not need to do the FORCE_COLOR.

However, that does not work for all commands, for example ls does not seem to accept this argument.

I was there too. Like said in the thread, there's no colored output because the command you're executing doesn't detect a TTY environment.
If you:

• Don't want to inherit the child stdout
• Don't know which command is going to be executed (then you don't know which of e.g --ansi or --colors can work)

Then you should spawn a PTY from node. You may use node-pty, but it is a hassle to install, and it doesn't support latest node versions. Instead, I suggest using this node package that I wrote.