stdout includes prompt + command on Windows

[mathiasbynens]

On this line: https://github.com/GoogleChromeLabs/jsvu/blob/905885652848add5f8fe27bb909057fe777974ab/engines/chakra/test.js#L29

stdout is equal to:

"\r\nC:\\Users\\jsvu>\"C:\\Users\\jsvu/.jsvu/engines/chakra\\chakra.exe\" \"C:\\Users\\jsvu\\AppData\\Local\\Temp\\3a4c2232c333e7ab7da85331c1dfe4e4\" \r\nHi!"

The expected value is only the actual stdout, which is:

"Hi!"

In case it matters, this happens after running a batch script chakra.cmd with the following contents:

"C:\Users\jsvu\.jsvu\engines\chakra\chakra.exe" %*

[SamVerschueren]

I'll try to have a look when I find some time :).

[mathiasbynens]

FWIW, adding @echo off to the batch script prevents the visual expansion from happening and works around this execa bug.

[SamVerschueren]

Hi @mathiasbynens. I looked into this and I can reproduce the issue with a simple ECHO Hello World in a hello.cmd file. However, this does not appear to be a execa bug.

const cp = require('child_process');

childProcess.exec('hello.cmd', (err, stdout) => {
    console.log(stdout);
    //=> '\r\nC:\\Users\\Sam\\Projects\\test>ECHO Hello World\r\nHello World\r\n'
});

I looked into the options of child_process and tried to Google for some answers to the question "Why this behaviour?". Couldn't find any...

So not sure how to continue from here. Do you happen to know someone who might know more? Should we open an issue in the Node.js repository?

[mathiasbynens]

I agree this is not strictly an execa bug, but rather a quirk of how Windows/cmd.exe works. If providing a cross-platform stdout that makes sense is a goal of this project, it would be nice if execa worked around it.

[mathiasbynens]

I should note that it’s unclear (to me) if it’s even possible to work around this behavior in a reliable/robust way.

[SamVerschueren]

Alright, I was too fast. I found the reason for this behaviour and also found a solution.

To run the hello.cmd file I wrote from the command line, you would have to use cmd.exe /c hello.cmd. This results in the exact same output as we are experiencing. However, cmd.exe has a /q flag which turns off the echo thingy, which you did manually with @echo off.

So in the background we use node-cross-spawn to make things easier. It already adds a couple of flags right here, but not the /q flag. I just checked manually in the execa code if cmd.exe was used as a command and pushed the /q flag onto the arguments and it worked.

Are there any downsides of always turning off echo? Is it ok to do it or can we break some behaviour?

[mathiasbynens]

I guess that would break cases where people rely on the current behavior — but it’s unclear if there are any. The behavior is weird, and relying on it seems even weirder, IMHO. What does @sindresorhus think?

[SamVerschueren]

I'm not really into batch files, but what does @echo off do exactly? I looked it up but couldn't find a decent answer. Does it only hide the executing command in this case? Or will/can it hide other information as well further down in the cmd file?

I totally agree that it's weird and IMO we should turn it off, if it doesn't have other implications.

[sindresorhus]

Yes, I think we should include the /q flag. I can't imagine anyone depending on this and if they do, they can just use a different module or child_process directly.

[SamVerschueren]

@mathiasbynens version 0.9.0 is released with this fix. Thanks for reporting.